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The opportimity oifered in preparing a fourth edition 
of the Manual of Photography for the press, has been 
embraced for the purpose of making some alterations in 
the aiTangements of the several divisions of the subject, 
and of placing thereby each particular phenomena in a 
clearer view. By this the amateur will advance more 
readily in his Photogi'aphic studies, and the experienced 
artist will find the references more easy to any particular 
mode of manipulation which he may desire to consult. 

All the most recent improvements have been compre- 
hended; the processes of Photogi'aphic etching have been 
embraced ; and, it is believed, nothing omitted which 
can serve to maintain the flattering position which the 
" Manual" has secured for itself as a standard work on 


London, March, 1854. , 


The rapidity with which the second edition of this work 
has been exhausted, is a most satisfactory proof that a 
collection within convenient compass of all the facts con- 
nected with the progress and practice of Photography, 
was required by the increasing number of amateurs and 
artists who are interested in its very beautiful phenomena. 

In the present edition a new system of arrangement has 
been adopted, which will, it is thought, prove generally 
convenient. The first division contains the history of the 
progress of Photogi'aphic discovery, in which the gi-eatest 
care has been taken to insm-e exactness, and to give to 
each discoverer the full merit of his labours: the date of 
publication being taken in all cases where it could possibly 
be obtained. 

The second division embraces the science of the art ; 
and it is a section to which the attention of the inteUigent 
student in Photography is particularly directed, as he 
may, by the knowledge he will thus acquire, relieve him- 
self from many of the annoyances attendant upon frequent 
failures, and probably advance himself in the path of new 
discovery. The manipulatory details, given with all 
necessary minuteness, ai-e included in the third division. 

A very large portion of the present volume consists of 
new matter — the Waxed Paper and the Collodion Pro- 
cesses, amongst other sections, may be refen-ed to ; and 


the appended chapter, On the Production of Pictui'es for 
the Stereoscope, will be found to afford much useful in- 
formation. The additional wood -cut illustrations which 
have been introduced will be found to render important 
aid to the amateur. I must acknowledge the ready as- 
sistance, in the way of correction and information, which 
has been afforded me by several of the most practised 
photographic artists of the metropolis. To Mr. Claudet 
and Mr. Home, in particular, I am indebted for many 
novel and most useful details in the practice of the 
Daguerreotype and the Collodion processes ; and to Mr. 
Sandford, who has furnished me with many valuable 
facts relating to the preparation of paper for Photography, 
I am under many obligations. Those gentlemen who 
have kindly hastened to supply me with the results of 
their practice, which is duly acknowledged in the text, 
will accept my thanks. In conclusion, let me hope that 
the arrangement of the present volume will be found an 
improvement upon the former editions, and that this 
Manual may deserve to maintain its place as as a Text- 
Book on Photography. 


London, Decemler, 1852. 


P.YPtT I. 


Early Eesearches on the Chemical Action of the Solar 
Eats ........ 3 


Heliography — The Process of M. Niepce . . .12 


Mr. H. Fox Talbot's Photogenic Drawings, Calotype, &c. 
Section I. Photogemc Drawing 
„ II. Calotj^e . 
„ III. Improvements in Calotype 
„ IV. Pictures on Porcelain 
„ V. Instantaneous Process 


Daguerreotype — The Discovery of M. Daguerre 

Section I. The Original Process of M. Daguerre 
„ II. Improvements in Daguerreotj^e 


The Photographic Processes on Paper of Sir John Herschel 48 
Section I. Cyanot^^^e . . . .48 

II. C'hrysotyiDe . . . .54 

III. Photographic Properties of Mercuiy . 57 

IV. Ferro-Tai-trate of Silver . . .58 
V. The Amphitype . . . .59 

VI. The Colom-iniT Matter of Flowers . 6 1 

rPE, &c. 













Miscellaneous Processes ..... 

Section I. Mr. Pontoii's process. (Bicliromate of 
Potash) . 
„ II. The Chromatype . 
,, III. The Ferrotj-pe 
„ IV. The Catalysotype 
„ V. Ferrocyanide of Potassium 
„ VI. The Fkiorot>T3e . 
„ VI.*Bromide of Silver and Mercurial Vapour 
„ VI r. Positive Photogi'aphs by One Process . 
„ VIII. On the Application of the Daguerreotype 

to Paper .... 

„ IX. Salts of Grold as Photographic Agents . 
„ X. The Influence of Chlorine and Iodine in 
rendei'ing Wood sensitive to Light 


Photographs on Glass Plates and Recent Improvements 
Section I. Precipitates of Silver Salts 




Portraiture by the Daguerreotype . 

General Summary of the History of Photography 








PAET 11. 


General Remarks on the Solar Agency producing Chemi- 
cal Change ....... 


Chemical Changes on Sensitive Preparations 
Section I. Nitrate of Silver 
„ II. Chloride of Silver 
„ III. Iodide of Silver . 
„ IV. Bromide of Silver 
„ V. Miscellaneous Salts of Silver 


The Theory or the Daguerreotype . 






On THE Photographic Registration OF Philosophical Instru- 

TiNic Power, and for Experiments on the Chemical Focus 1.39 
Section I. Photographic Registration . . 139 
„ II. Instniments for Measuring Actinic Varia- 
tions, &c. .... 143 
The Photographometer . . 143 
The Focimeter . . .145 
The Dynactinometer . . 146 

Thermography ....... 151 


On the Possibility of Producing Photographs in their Na- 
tural Colours ...... 158 

On Lenses for the Photographic Camera . . . 163 

?xrt: III. 



Selection of Paper for Photographic Purposes . . 176 


On the Apparatus necessary for the first Practice of Pho- 
tography on Paper . . . . . .183 


On the modes of Manipulation adopted in the Preparation 
of Sensitive Papers . . . . . .193 

Section I. Nitrate of Silver . . . 193 

n. Chloride of SUver . . .194 

„ III. Iodide of Silver . . . .197 


On Fixing the Photogpjo'hic Pictures . . . 199 


The Calotype as now practised, and its Modifications . 206 

Section I. Calotype on Paper . . . 206 

„ II. Calotype on Gelatine or Albumen . 222 

„ III. Calotype Process on Waxed Paper . 227 



The Dagtterreottpe ...... 231 

Section I. Daguerre's improved Manipulation . 231 
„ II. Polishing the Plate . . . 235 

„ III. To give the Sensitive Surface to the Plate 236 
„ IV. To Develope the Image formed on the 

Plate . . . . .243 

„ V. Fixing the Daguerreotype Image . 245 

„ VI. Simplification of the Daguerreoty|De . 248 

The Collodion Process ..... 252 


The use of Albumen on Glass Plates, &c. . . . 276 

Section I. Albumen on Glass . . . 276 

„ II. Mr. Malone's Process . . .278 

„ III. M. Martin's Process . . .280 

„ IV. Miscellaneous Processes . . . 282 
„ V. Positive Photogra^jhs from Etchings on 

Glass Plates . . . .283 


On the Production of Positive Photographs by the use of 
THE Salts of Iodine ...... 285 


General Eemarks on the Use of the Camera Obscura — 
The Photographic Pentagraph .... 298 
Section I. Buildings, Statues, Landscapes, and Fo- 
liage . . . . .298 
„ II. Portraits from the Life . . . 300 
„ III. Photographic Pentagraph . . 302 

The Stereoscope ...... 304 


Photographic Engraving ..... 314 

Appendix ....... 321 

Photographic Patent Eight . . . .321 

Correspondence of English and French Weights and 
Measures . ... 324 

Index ...... 325 







It is instructive to trace tlie progi-ess of a tliscoveiy, fi-om tlie 
fii-st indication of a truth, to the period of its fiill development, 
and its application to jiiu-poses of ornament or utility. The 
progress of discoveiy is ordinarily slow, and it often happens that 
a gi-eat fact is allowed to lie dormant for years, or for ages, which, 
when eventually revived, is found to render a fine interpretation 
of some of Nature's haimonious phenomena, and to minister to 
the wants or the pleasm-es of existence. Of this position, Photo- 
gi-aphy is peculiarly illustrative. 

The philosophers of antiquity appear to have had their atten- 
tion excited by many of the more striking characters of light : 
yet we have no account of their having observed any of its che- 
mical influences, although its action on colom-ed bodies — deepen- 
ing their colour in some cases, and dischai-giug it in others — 
mus-t have been of every-day occiu-rence. The only facts which 
they have recorded are, that some precious stones, particularly 
the amethyst and the opal, lost their sparkle by prolonged 
exposiu-e to the rays of the sun. 

It has been stated — ^but on doubtful authority — that the jug- 


glers of India were for many ages in possession of a secret 
process, by wkicli tliey were enabled in a lirief space to copy the 
profile of any individual Ijy the agency of light. However this 
may have been, it does not appear that they know anything of 
such a process in the present day. 

The alchemists, amidst the multiplicity of theii" processes — in 
their vain search for i\\e pliUosoplipys stone, and the elixir vitce — 
stimibled upon a jDeculiar combination of silver with chlorine, 
which they called horn-silver — as, by fasion, the white powder 
they obtained by precipitation was convei'ted into a hom-like 
substance. They observed that this horn-silver was blackened 
by Kght, and as they taught that "silver only diflfered fi'om gold 
in being mercmy intei-penetrated by the siilphiu-eous principle 
of the sun's rays," they concluded that this change was the 
commencement of the process by which their di-eams were to be 
realized. Failing, however, to produce gold from hom-silver, 
the fact of its blackening was simply recorded, and no fiu-ther 
investigations were made into tliis remarkable ^^henomenon. 

Petit, in 1722, noticed that solutions of nitrate of potash and 
miu-iate of ammonia ciystallized more readily in the light than 
they did in darkness. 

The illustrious Scheele (1777), in his excellent Traite de 
VAir et clu Feu, gave the world the first philosophical examina- 
tion of this pecviliar change in a salt of silver, and proved the 
dissimilar powers of the different rays of light in eflecting this 
change. He writes, " It is well known that the solution of 
silver in acid of nitre poiu-ed on a piece of chalk, and exposed to 
the beams of the sun, gi'ows Ijlack. The light of the sun reflected 
from a white wall has the same effect, but more slowly. Heat 
without light has no efiect on this mixtiu-e." Again, " Fix a 
glass prism at the window, and let the refi-acted sim-beams fall 
on the floor; in this coloiu'ed light put a paper strewed with 
luna cornua, and you will observe that this horn-silver gTOws 
sooner black in the \"iolet I'ay than in any of the other i"ays." 

Senebier repeated these experiments, and he states that he 
foimd chloride of silver darkened in the violet ray in fifteen 
seconds to a shade which requii-ed the action of the red ray for 
twenty miuutes. He also experimented on the influence of light 
in bleaching wax. 

In the PMlosopMcal Transactions for 1798 will be found a 
memoii' by Count Eumford, entitled, "An Inquiiy concerning 
the Chemical Properties that have been attributed to Light." In 
tills paper a number of experiments are brought forward to prove 
that all the effects produced upon metallic solutions by bright 
sunshine, can be obtained by a prolonged expos\u-e to a tempe- 


rature of SIO'^ Fahrenheit. We ai'e now, liowever, in a position 
to show that the chemical eflects produced by raj's of dark heat, 
are of a Tery diffei-ent character £i-om those iisually attributed to 
light. Mr. Eobert Harrap, in a eommimication to Xicholson's 
Journal in 1802, refuted the exj)eriment of Count Rumford, 
showing that sevei-al salts of mercury were reduced by light 
alone, and not heat. 

In 1801, Ritter proved the existence of rays a considerable 
distance beyond the visible spectrum, which had the property of 
speedily blackening cliloride of silver. These researches excited 
the attention of the scientific world : M. Berard, Seebeck, Ber- 
thollet, and others, directed theii- attention to the pecidiar con- 
dition of the difierent rays in relation to their kiniinous and 
chemical influences; whUe Sii" William Hei"schel and Sii* Heniy 
Englefield investigated the calorific powers of the colomed rays, 
and were followed in these investigations by Seebeck and Wimsch. 
Dr. WoUaston piu-sued and published an interesting series of 
experiments on the decomposition efi"ected by light on gum- 
guaiacum. He found that paper washed with a solution of this 
giun in spirits of wine, had its yellow colour rapidly changed to 
green by the violet rays, while the red rays had the property of 
restoring the yellow hue. Sir Himiphiy Davy observed that 
the puce-colom-ed oxide of lead became, when moistened, red 
by exposme to the red i-ay, and black when exposed to the violet 
ray ; and that the gi'een oxide of merciirj^, although not changed 
by the most refrangible rays, speedily became red in the least 

Morichini and Configliachi, M. Berard, and more recently, Mrs. 
SomerAdlle made some cmious experiments on the power of the 
"violet rays to induce magnetism in steel needles. Seebeck and 
Berzelius investigated this involved subject: it has again and 
again engaged the attention of experimentalists ; but to the 
present time it must be regarded as an imsettled point, whether 
magnetism can be induced in steel by the solai" rays. 

A statement has been made by the French, to the efiect that 
M. Charles was in possession of a process by which portraits 
could be obtained by the agency of sunlight, producing a dark 
impression upon a prepared surface. This is, however, exceed- 
ingly doubtful, and even the Abbe Moigno, in hLs Repertoire, 
states, that M. Charles never disclosed any fact connected with 
this discovery, and that he left no evidence behind him of being 
in possession of sixch a process. 

In addition to the interesting facts already mentioned, it ■v\'ill 
be insti-uctive to add a few particulars of other inquiries pui- 
sued about the same time on various phenomena connecting 


themselves wdth tlie solar radiations. Although these do not 
bear directly on Photography, they stand in very close relation 
with it, and will seiwe possibly to indicate lines of reseai'ch which 
have not been fixlly followed out. 

Desmortiers in 1801 published a paper in. Gilhevt's Annals, 
entitled, " Eecherches siu' la Decoloration spontanea du Blen de 
Prusse," subsequently translated into Nicholson's Journal, in 
which he has mentioned the influences of the solar rays in 
producing the change. Bockman aboiit the same time observed 
that the two ends of the spectnun acted differently on phos- 
phorus; and Dr. Wollaston, examining the chemical action of 
the rays of the spectiiim, ai-rived at nearly the same results as 
Eitter. He states, " This and other effects usually attributed 
to light are not in fact owing to any of the rays usually per- 

Wedgwood was certainly the fii*st person who made any 
attempts to use the siuibeam for deHneating the objects it illu- 
minated: it is therefore necessary that some more particular 
account should be given of his processes. In 1802, he published 
a paper in the Joiu-nal of the Royal Institution, under the fol- 
lo\\-ing title : "An Account of a Method of Copying Paintings 
upon Glass, and of making Profiles by the Agency of Light upon 
Nitrate of Silver ; with Obseiwations by H. Davy." From this 
communication, the following extracts, containing the more 
impoi-tant indications, are made. 

" White paper, or white leather, moistened with solution of 
nitrate of silvei*, undergoes no change when kept in a dark place, 
but, on being exposed to the daylight, it speedily changes colour, 
and after passing throiigh different shades of gTay and brown, 
becomes at length nearly black. The alterations of colour take 
place more speedily in propoilion as the Hght is more intense. 
In the dii-ect beam of the sun, two or thi-ee minutes ai'e sufficient 
to produce the full effect ; in the shade several houi's are required; 
and light transmitted throxigh different coloured glasses acts 
upon it with different degTces of intensity. Thus, it is found 
that red rays, or the common simbeams, passed thi'ough red glass, 
have very little action upon it ; yellow and green are more 
efficacious ; but blue and -violet light produce the most decided 
ajid powerfiil effects. 

" When the shadow of any figiu'e is thi'own upon the prepared 
siu-face, the part concealed by it remains white, and the other 
parts speedily become dark. For copying paiutmgs on glass, 
the solution should be applied on leather; and in this case it is 
more readily acted on than when paper is used. After the 
colour has been once fix:ed on the leather or paper, it cannot be 


removed by the application of water, or -water and soap, and it 
is in a liigh degree permanent. The copy of a painting, or the 
ja'ofile, immediately after being taken, must be kept in an 
'ibscui-e place; it may, indeed, be examined in the shade, but in 
this case the exposure shoiild be only for a few minutes : by the 
light of candles or lamps, as commonly employed, it is not 
sensibly affected. No attempts that have been made to prevent 
the uncoloured parts of the copy or profile fi*om being acted 
upon by Hght, have as yet been successful. They have been 
covered by a thin coating of fine vamish, but this has not 
destroyed theii' suscej^tibility of becoming coloiu-ed ; and even 
after repeated washings, sufficient of the active part of the 
saline matter will adhere to the white parts of the leather or 
paper to cause them to become dark when exposed to the rays 
of the Sim. Besides the applications of this method of copying 
that have just been mentioned, there are many others ; and it 
will be useful for making delineations of all such objects as are 
possessed of a textui'e partly opaque and partly transparent. 
The woody fibres of leaves, and the wings of insects, may be 
pretty accurately represented by means of it ; and in this case it 
is only necessaiy to cause the dii-ect solar light to pass thi-ough 
them, and to receive the shadows upon leather. 

" The images foi-med by means of a camera obscm-a have been 
found to be too faint to produce, in any moderate time, an effect 
upon the nitrate of silver. To copy these images was the first 
object of Mr. "Wedgwood in his researches on the subject ; and 
for this purpose he fii'st used nitrate of silver, which was 
mentioned to him by a friend as a substance very sensible to 
the influence of light ; but all his numerous experiments as to 
their primary end proved unsuccessful. In following these 
processes, I have found that the images of small objects, pro- 
duced by means of the solar microscope, may be copied without 
difficulty on prepared paper. This will probably be a useftd 
application of the method ; that it may be employed successfully, 
however, it is necessaiy that the paper be placed at but a small 
distance from the lens. {Davy.) 

" In comparing the effects produced by light upon muriate of 
silver with those produced iipon the nitrate, it seemed evident 
that the muriate was the most susceptible, and both were more 
readily acted upon when moist than when dry — a fact long ago 
known. Even in the twilight, the colou.r of the moist mimate 
of silver, spread upon paper, slowly changed from white to faint 
violet ; though, imder similar circumstances, no immediate 
alteration was produced upon the nitrate. 

" Nothing but a method of preventing the imshaded parts of 


the delineations fi^om being coloured by exposure to the day, is 
wanting to render this process as useful as it is elegant." 

An expeiiment on the dark rays of Ritter, by Dr. Young, 
included in his Bakerian Lecture," is a very important one. Dr. 
Young, after referi-iug to the experiments of Eitter and Wol- 
laston, goes on to say : " In order to complete the comparison of 
their properties (the chemical rays) with those of visible light, 
I was desirous of examining the effect of their reflection from a 
thin plate of air capable of producing the well-known rings of 
colom-s. For this purpose I formed an image of the rings, by 
means of the solar microscope, with the appai-atus which I have 
described in the Journals of the Royal Institution ; and I threw 
this image on paper dipped in a solution of nitrate of silver, 
placed at the distance of about nine inches from the microscope. 
In the course of an horn-, portions of three dark rings were very 
distinctly visible, much smaller than the brightest rings of the 
coloiu'ed image, and coinciding very nearly, in their dimensions, 
with the rings of violet light that appeared upon the interpo- 
sition of violet glass. I thought the dark rings were a little 
smaller than the violet rings, but the difference was not suffi- 
ciently great to be accurately ascei-tained : it might be as much 
as ^Q or ^Q of the diameters, but not greater. It is the less 
surpiising that the difference should be so small, as the dunen- 
sions of the coloui-ed rings do not by any means vary at the 
violet end of the spectrum so rapidly as at the red end. The 
experiment in its present state is sufficient to complete the 
analogy of the invisible with the visible rays, and to show that 
they are equally liable to the general law, which is the principal 
subject of this paper :" that is the interference of light. 

M. B. G. Sage, in the Journal de Physique, 1802, mentions 
a fact observed by him, that " the realgar which is sublimated at 
the Solfaterra under the form of octahech-al crystals, known 
under the name of ruby of arsenic, effloresces by the light ; " 
and that ordinaiy native realgar from Japan changes to orpi- 
ment by exposure to sunshine. 

In 1806, Vogel exposed fat, carefully protected from the 
influence of the air, to light, and found that it became in a short 
time of a yellow colour, and acquii-ed a high degree of rancidity. 
Vogel subsequently discovered that j^hosphorus and ammonia 
exposed to the sim's rays were rapidly converted into phosj^hu- 
retted hydrogen, and a black powder, phosphuret of ammonia. 
He also noticed that the red rays produced no change on a 
solution of corrosive sublimate (bichloride of merciuy) in ether, 

* PldlosopMcal Transactions, 1804. 


but that tlie blue rays rapidly decomposed it. Dr. Davy, much 
more recently, repeated a siuiilar set of experiments to those of 
Yogel. He found that corrosive sublimate was not changed by 
exposui'e ; but that the Liquor Hydrary. Oxymur. of the old 
London Pharmacopoeia quickly vmdei-went decomposition in the 
sunshine, depositing calomel (chloride of merciuy). 

Seebeck, in and subsequently to 1810, made some important 
additions to omt knowledge of the influences of the solar 
radiations, the most striking of his statements being the 2>'>'o- 
duction of colour on chloride of silver ; the violet rays rendering 
it bro-wTi, the blue producing a shade of blue, the yellow pre- 
serving it white, and the red constantly gi'v'ing a red colour to 
that salt. Sii' Hemy Englefield, about the same time, was 
enabled to show that the phosphorescence of Canton's phos- 
• phoiois was gi'eatly exalted by the blue rays. 

Gay-Lussac and Thenard, being engaged in some investigations 
on chlorine, on which elementary body Da^y was at the same 
time experimenting, observed that hycb'ogen and chlorine did 
not combine in the dark, but that they combined with gTeat 
rapidity, and often with explosion, in the sunshine, and slowly 
in ditfused light. Seebeck collected chlorine over hot water, 
and, combining it with hych-ogen, placed difierent portions of it 
in a yellowish-red beU glass and in a blue one. In the blue 
glass combination took place immediately the mixtiu'e was 
exposed to daylight ; but without explosion. The mixture in 
the red glass was exposed for twenty minutes without any 
change ; but it was fomid that the chlorine had undergone 
some alteration, probably a similar one to that subsequently 
noticed by Dr. Draper, who found that chlorine having been 
exposed to simshine would unite "with hych-ogen in the dai-k. If 
the gases were placed in a white glass and exj)osed to sunshine, 
they exjDloded ; but if the gas had been preidously exposed to 
the action of the solar i-adiations in the yellow-red glass, it 
combined with hycb'Ogen in the wliite glass in the brightest 
sunsliine ■v\dthout any explosion. 

BerzeHus noticed some peculiar conditions in the action of 
the solar rays upon the salts of gold ; and Fischer pursued some 
researches on the influence of the prismatic rays on horn-silver. 

The most important series of researches, however, were those 
of Bei-ard in 1812, which were examined and reported on by 
BerthoUet, Chaptal, and Biot. These philosophers write : " He 
(M. Berard) found that the chemical intensity was gi-eatest at 
the violet end of the spectrmn, and that it extended, as Bitter 
and WoUaston had observed, a Kttle beyond that extremity. 
When he left substances exposed for a certain time to the action 


of each ray, he observed sensible effects, though with an inten- 
sity continually decreasing in the indigo and blue rays. Hence 
we must consider it as extremely probpble, that if he had been 
able to employ reactions still more sensible, he would have 
observed analogous eifects, but still more feeble, even in the 
other rays. To show clearly the great disproportion which exists 
in this respect between the energies of different rays, M. Berard 
concentrated, by means of a lens, all that part of the spectrimi 
which extends from the green to the extreme violet ; and he con- 
centrated, by means of another lens, all that portion which ex- 
tends from the green to the extremitij of the red. This last 
pencil formed a ivhite jwint so brilliant that the eyes toere scarcely 
ahle to endure it ; yet the muriate of silver remained exposed more 
than two hours to this brilliant point of light iviihout tmdergoing 
any sensible alteration. On the other hand, when exposed to 
the other pencil, which was much less bright and less hot, it was 
blackened in less than six minutes." Tliis is the earliest inti- 
mation we have of any hypothesis that the luminous and chemical 
powers may be due to dissimilar agencies. On this, the Com- 
missioners remark : — " If we wish to consider solar light as 
composed of three distinct substances, one of which occasions 
light, another heat, and the third chemical combinations, it will 
follow that each of these substances is separable by the prism 
into an infinity of different modifications, like light itself; since 
we find by experiment, that each of the three properties, chemical, 
colorHic, and caloriRc, is spread, though unequally, over a cer- 
tain extent of the spectrum. Hence we must suj)pose, on that 
hypothesis, that there exist three spectrums, one above another ; 
namely, a calorific, a colorific, and a chemical sj)ectrum. We 
miist likewise admit that each of the substances which compose 
the three spectrums, and even each molecule of imequal refran- 
gibility which constitutes these substances, is endowed, like the 
molecules of visible light, with the property of being polarized 
by reflection, and of escaping from reflection in the same positions 
as the Imninous molecules, &c." 

From the time when the difficulty of fixing the photographs 
which they obtained, stopped the progress of DavyandWedg•^vood, 
no discoveries were made until 1814, when M. Niepce, of Chalons, 
on the Soane, appears to have first dhected his attention to 
the production of pictures by light. 

It does not seem that his early attempts were very successful ; 
and, after pursuing the subject alone for ten years, he, from an 
accidental disclosure, became acquainted with M. Daguerre, who 
had been for some time endeavouring, by varioiis chemical pro- 
cesses, to fix the images obtained with the camera obscura. In 


December, 1829, a deed of copartneiy Tvas executed between M. 
Xiepce and M. DagneiTe, for m\itually investigating the subject. 

M. Niepce had named his discoA'eiy Heliogi-aphy.* In 1827, 
he presented a paper to the Royal Society of London, on the 
subject ; but as he kept his process a secret, it conld not, agi-ee- 
ably with one of theii* laws, be received by that body. This 
memoir was accompanied with several heliographs on metal 
(plated copper and pewter) and on glass plates ; which were 
aftei'wards distributed in the collections of the cxmons, some of 
them still existing in the possession of Mr. Robert Brown, of 
the British Museum. They pi-ove M. Xiepce to have been then 
acquainted with a method of fonning pictiu-es, by which the 
lights, semi-tints, and shadows, were represented as in nature ; 
and he had also succeeded in rendei-ing his Heliographs, when 
once formed, imjieiwious to the fiuiher effects of the solar rays. 
Some of these specimens appear in a state of advanced etchings ; 
but this was accomplished by a process similar to that piu-sued 
in common etchings. 

The ease with which nitric acid could be applied to etch 
these Heliographic plates will be apparent when the process of 
obtaining the pictures is undei-stood. 

* Sun-drawing : a more appropriate name than Photography, since it remains 
a problem (1853) of diflSeult solution, whether Light, or some agent associated 
with Light, is active in producing the chemical changes we ai-e considering. 



M. NiEPCE "was tlie first inquirer who appears to have produced 
permanent pictm-es by the influence of the sun's rays. This 
process — Heliography — is in many resj^ects peculiax*, which 
renders it necessary, although his preparation was only acted on 
by an exposiu'e of many hoiu's to fiill sunshine, to give a parti- 
cidar account of it ; the more so, as some points of considerable 
interest requii-e fiu-ther elucidation. 

The substance employed by M. Niepce was asphaltum, or 
bitmnen of Judea, He thus directs its preparation : — " I about 
half fill a wine-glass with this pulverized bitumen ; I pour upon 
it, drop by ch-op, the essential oil of lavender,* imtil the bitumen 
is completely satiu'ated. I afterwards add as much more of the 
essential oil as causes the whole to stand about thi-ee lines above 
the mixtiu'e, which is then covered and submitted to a gentle 
heat until the essential oil is fully impregnated with the colouring 
matter of the bitumen. If this varnish is not of the requii-ed 
consistency, it is to be allowed to evaporate slowly, without 
heat, in a shallow dish, care being taken to protect it from 
moisture, by which it is injured, and at last decomposed. In 
winter, or during rainy weather, the precaution is doubly neces- 
sary. A tablet of plated silver, or well cleaned and wai-m glass, 
is to be highly jiolished, on which a thin coating of the varnish 
is to be appKed cold, with a light roll of very soft skin : this will 
impart to it a fine vermilion coloiu-, and cover it with a veiy thin 
and equal coating. The plate is then placed upon heated iron, 
which is "\vrapped round "svith several folds of paper, fi-om which 
by this method all moisture had been pre"viously expelled. 
When the varnish has ceased to simmer, the plate is withdi'awn 
fi'om the heat, and left to cool and dry in a gentle temperature, 
and protected from a damp atmosphere. In this part of the 
operation a light disk of metal, with a handle in the centre, 

* The English oil of lavender is too expensive for this purpose. An article 
sold as the French oil of lavender, redrawn, is very much cheaper, and answers 
in every respect as well, if not better. 


slioiild be held before tbe mouth, in order to condense the mois- 
ture of the breath." 

The plate thus prepared is now in a fit state for use, and may- 
be immediately fixed in the correct focus of the camera. After 
it has been exposed a sufficient length of time for receiving the 
impression, a very faint outhne alone is visible. The next opera- 
tion is to bring out the hidden pictvu'e, which is accomplished by 
a solvent. 

This solvent must be carefully adapted to the piu-jjoses for 
"which it is designed : it is difficult to fix vdih cei-taiaty the pro- 
portions of its components, but in all cases it is better that it 
be too weak than too strong ; in the former case the imao-e 
does not come out strongly ; in the latter it is comjjletely de- 
stroyed. The solution is prepared of one part — not by weight, I ' 
but volimie — of the essential oil of lavender, poiu-ed ujwn ten ■ 
parts, by measm-e also, of oil of white petroleum. The mixture \ 
which is fii'st milky, becomes clear ra two or three days. This •■ 
compound will act until it becomes satiu-ated with the asphaltimi, 
which state is readily distinguished by an opaque apjiearance, and 
dark brown colour. A tin vessel somewhat larger than the pho- 
tographic tablet, and one inch deep, must be provided. This is 
to have as much of the solvent in it as will cover the plate. The 
tablet is plimged into the solution, and the operator, obseiwing 
it by reflected light, begins to see the images of the objects to 
which it has been exposed slowly unfolding then.' forms, though 
still veiled by the gi-adually darkening supernatant fluid. The 
plate is then Hfted out, and held in a vertical position, till as 
much as possible of the solvent has been allowed to drop away. 
When the dropping has ceased, we proceed to the last, and not 
the least important operation, of washing the plate. 

This is performed by carefully placing the tablet upon a 

board, b, fixed at a large 
angle, in the trough A a, the 
sujjports being joined to it 
by hinges, to admit of the 
necessary changes of inclina- 
tion, under difiercnt circum- 
stances : two small blocks, 
not thicker than the tablet, 
are fixed on the board, on 
which the plate rests. Water 
must now be slowly povu'ed 
'" upon the upper pai-t of the 

board, and allowed to flow evenly over the sui-face of the picture. 
The descending stream clears away aU the solvent that may yet 


adhere to the varnish. The plate is now to be di'ied with gi"eat 
care by a gentle eTaporation : to preser^'e the j)ictm'e, it is 
requisite to cover it up frcm the action of light, and protect it 
from hmnidity. 

The vai-nish may be applied indifferently to metals, stone, or 
glass; but M. Nieijce prefers cojDper plated with silver. To 
take copies of engTa'v'ings, a small quantity of wax is dissolved 
in essential oU of lavender, and added to the vamish ah-eady 
described : the engTa\TJig, first varnished over the back, is placed 
on the siuface of the prepared tablet, face towards it, and then 
exposed to the action of the light. In the camera obscui'a an 
exposiu-e of from six to eight hours, varying with the intensity 
of light, is requii'ed ; while fi'om foiu' to six hours is necessaiy 
to produce a copy of an engi'aving. The pictiu-e, in the fij^t 
instance, is represented by the conti"ast between the polished 
sUver and the varnish coating. The discoverer aftei-wards 
adopted a plan of darkening the sUver by iodine, which appears 
to have led the way to Daguerre's beautiful process. To darken 
the tablet, it was placed in a box in which some iodine was 
strewed, and watched until the best effect was produced. The 
varnish was afterwards removed by spiiit of wine. 

Of the use of glass plates M. Kiepce thus speaks : — " Two 
exjjeriments in landscape upon glass, by means of the camera, 
gave me results wliich, althoi^gh imperfect, appear deserving of 
notice, because this vai'iety of application may be brought more 
easily to perfection, and in the end become a more interesting 
department of heliogTaphy. 

" In one of these trials the light acted in such a way that the 
varnish was removed in proportion to the intensity with which 
the light had acted, and the pictui-e exhibited a more marked 
gradation of tone ; so that, viewed by transmitted light, the 
landscape produced, to a certain extent, the well-known effects 
of the diorama. 

" In the second trial, on the contrary, the action of the 
Imninous fluid having been more intense, the parts acted upon 
by the strongest lights, not having been attacked by the solvent, 
remained transparent ; the difference of tone resulted from the 
relative thickness of the coatings of varnish. 

" If this landscape is viewed by reflection in a miiTor, on the 
varnished side, and at a certain angle, the effect is remarkably 
striking ; while, seen by transmitted light, it is confused and 
shapeless : but, what is equally surprising, in this position the 
mimic tracery seems to affect the local colour of the objects." 

A statement that M. I^iepce was enabled to engi-ave by light, 
went the round of the press ; but this does not a^jpear to have 


been the case. All tliat the author of heHogi-aphy effected, was 
the etching of the plate, after it had undergone its varioxxs 
processes, and the diuwing was completed by the action of nitric 
acid in the usual manner : the parts of the coj)perplate pro- 
tected by the varnish remained, of course, unacted on, whilst 
the other pai-ts were rapidly attacked by the acid. Niepce re- 
marks that his process cannot be used dviring the winter season, 
as the cold and moistiu-e render the varnish brittle, and detach 
it from the glass or metal. 

M. Niepce afterwards used a more unctuous varnish com- 
posed of bitumen of Judea, dissolved in animal oil of Dijypel. 
This composition is of much greater tenacity and higher colour 
than the formei", and, after being apj^lied, it can immediately be 
submitted to the action of light, which appears to render it solid 
more quickly, from the greater volatility of the animal oil. M. 
Daguerre remai^ks, that this very propei'ty diminishes still 
fm-ther the resources of the process as respects the lights of the 
drawings thus obtained. These processes of M. Niepce were 
much improved by M. Daguerre, who makes the following 
remarks on the subject : — 

" The substance which should be used in preference to bitu- 
men is the residuum obtained by evaporating the essential oil of 
lavender, which is to be dissolved in alcohol, and applied in an 
extremely thin wash. Although all bituminous and resinous 
substances are, without any exception, endowed with the same 
property — that of being affected by light — the i^refei-ence ought 
to be given to those which are the most unctuous, because they 
give greater finnness to the di-awings. Several essential oils 
lose tliis character when they are exposed to too strong a 

" It is not, however, from the ease with which it is decomposed, 
that we are to prefer the essential oil of lavender. There ai-e, 
for instance, the resins, which, being dissolved in alcohol, and 
spread upon glass or metal, leave, by the evaporation of the 
spiiit, a very wliite and infinitely sensitive coating. But this 
greater sensibility to light, caused by a quicker oxidation, 
renders also the images obtained miich more liable to injmy 
from the agent by which they were created. They grow faint, 
and disappear altogether, when exposed but for a few months 
to the sun. The residuum of the essential oil of lavender is 
more effectually fixed, but even this is not altogether unin- 
fluenced by the eroding effects of a direct exposure to the 
sun's light. 

" The essence is evaporated in a shallow tlish by heat, till the 


resinous residuum acquii-es such a consistency, tliat when cold, 
it rings on being struck vntli the poiut of a knife, and flies ofi" 
in pieces when separated from the dish. A small quantity of 
this material is aftenvards to be dissolved in alcohol or ether ; 
the solution formed should be transparent, and of a lemon-yellow 
coloiu'. The clearer the solution, the more delicate will be the 
coating on the plate : it must not, however, be too thin, because 
it would not thicken or spread out into a white coat ; indispen- 
sable requisites for obtaining good effects in photogi-aphic 
designs. The use of the alcohol or ether is to facilitate the 
application of the resin under a very attenuated form, the spmt 
being entirely evaporated before the light effects its delineations 
on the tablet. In order to obtain gTeater vigour, the metal 
ought to have an exquisite polish. There is more charm about 
sketches taken on glass plates, and, above all, much greater 

"Before commencing operations, the experimenter must care- 
fully clean his glass or metal plate. For this purpose, emeiy, 
reduced to an impalpable powder, mixed wdth alcohol, may be 
used ; applying it by means of cotton-wool : but this part of the 
process must always be concluded by diy-poHshing, that no trace 
of moistui'e may remain on the tablet. The plate of metal or 
glass being thiis prepared, in order to supply the wash or coating, 
it is held in one hand, and with the other, the solution is to be 
poured over it from a flask or bottle having a wide mouth, so 
that it may flow i-apidly, and cover the whole siu-face. It is at first 
necessary to hold the plate a little inclined j but as soon as the 
solution is poiu'ed on, and has ceased to flow freely, it is raised 
perpendicrdarly. The finger is then passed behind and below 
the plate, in order to di'aw ofi" a poi'tion of the Hquid, which, tend- 
ing always to ascend, would double the thickness of the covering : 
the finger must be Aviped each time, and be passed very rapidly 
along the whole leng-th of the plate from below, and on the side 
opposite the coating. "When the liquid has ceased to iim, the 
plate is chied in the dark. The coating being well chied, it is 
to be placed in the camera obscm-a. The time required to pro- 
cui'e a photogi-aphic copy of a landscape is from seven to eight 
hom's ; but single monuments strongly illuminated by the sun, 
or very bright in themselves, are copied in about three hours. 

" When operating on glass it is necessaiy, in order to increase 
the light, to place the plate upon a piece of paper, with great 
care that the connection is perfect over every part, as, other- 
wise, confusion is produced in the design by imperfect reflection. 

" It frequently happens that when the plate is removed from 


tlie camera, there is no trace of any image upon its surface : it 
is therefore necessary to use another process to biing out the 
hidden design. 

" To do this, pro-\-ide a tin vessel, larger than the tablet, 
having all round a ledge or border 50 millimeters (2 English 
inches) in depth. Let this be three-quai-tei"s full of the oil of 
petroleum ; fix your tablet by the back to a piece of wood which 
completely covers the vessel, and place it so that the tablet, face 
downwards, is over but not touching the oil. The vapoiu" of the 
petroleum penetrates the coating of the plate in those parts on 
which the light has acted feebly ; that is, in the portions which 
corresjiond to the shadows, imparting to them a transparency 
as if nothing were there. On the contrary the points of the 
resinous coating, on which light has acted, having been rendered 
impei-Aious to the vapoiu', remain imchanged. 

"The design must be examined fi'om time to time, and with- 
drawn as soon as a vigorous efiect is obtained. By lU'ging the 
action too far, even the strongest lights wiU be attacked by the 
vapoTU', and disappear, to the destmction of the piece. The pic- 
ture, when finished, is to be protected from the dust by being 
kept covered ^vith a glass, which also protects the silver plate 
from tarnishing." 

It may perhaps appear to some that I have needlessly given 
the particulars of a process, now sxiperseded by others, possessing 
the most infinite sensibility ; producing in a few minutes a better 
efiect than was obtained by the heliographic process in several 
hours. There are, however, so many cra-ious facts connected 
■with the action of light on these resins, that no treatise on pho- 
tography could be considered complete ^^'ithout some description 
of them ; and this process is now revived ■with a view to the pro- 
duction of etchings directly fi'om nature. 

M. Daguerre remarks, that numerous experiments tried by 
him "w-ith these resinous preparations of M. Niepce, prove that 
light cannot fall upon a body without leaA^ing traces of decompo- 
sition; and they also demonstrate that these bodies possess the 
power of renewing in darkness, what has been lost by luminous 
action, pro^dded total decomposition has not been eflected. This 
heKographic process must be regarded as the earhest successful 
attempt at fixing on solid tablets the images of the camera ob- 
scura, and at developing a dormant image. 



Section I. — Photogenic Drawing, 

On tlie 31st of Jamiaiy, 1839, six montlis prior to the publica- 
tion of M. Dagiiei"re's process, Mr. Fox Talbot communicated to 
the Royal Society his photographic discoveries, and in Febi-uary 
he gave to the world an accoimt of the process he had devised 
for preparing a sensitive paper for photographic ch'awings. In 
the memoir read before the Royal Society, he states — " In the 
spring of 1834, 1 began to put in practice a method which I had 
devised some time pre\"iously, for employing to pm-poses of utility, 
the very cui'ious property which has been long known to che- 
mists to be possessed by the nitrate of silver, namely, its dis- 
coloration when exposed to the violet rays of light." Prom 
this it appears that the EngHsh philosopher had pursued his 
researches ignorant of what had been done by others on the 
Continent. It is not necessaiy to enlarge, in this place, on the 
merits of the two discoveries of Talbot and Daguerre; but it 
may be as well to show the kind of sensitiveness to which Mr. 
Talbot had aiTived at this early period, in his pre^jarations ; 
wliich will be best done by a brief extract from his own com- 

"It is so natural," says this experimentalist, "to associate the 
idea of labour with great complexity and elaborate detail of exe- 
cution, that one is more struck at seeing the thousand florets of 
an Ayrostis depicted with all its capillaiy branchlets, (and so 
accvu-ately, that none of all this multitude shall want its little 
bivalve calyx, requii'ing to be examined through a lens), than 
one is by the pictm-e of the large and simple leaf of an oak or a 
chestnut. But in trath the difficulty is in both cases the same. 
The one of these takes no more time to execute than the other; 
for the object which woidd take the most skilfid artist days or 
weeks of labour to trace or to copy, is eflected by the boundless 
powers of natural chemistry in the space of a few seconds." And 
again, "to give some more definite idea of the rapidity of the 
process, I will state, that after various trials, the nearest valua- 

Talbot's photogenic drawing. 19" 

tion wMch I could make of tlie time necessary for obtaining tlie 
picture of an object, so as to have pretty distinct outlines, when 
I employed the full sunshine, was half a second.'''' This is to be 
imderstood of the paper then used by Mr. Talbot for taking ob- 
jects by means of the solar microscope. 

In the Philoso'phical Magazine, Mr. Fox- Talbot published the 
first accoimt of his Photogenic exjieriments. This term was in- 
troduced by this gentleman : and his experiments cannot be 
better described than in liis own words. " In order to make 
what may be called ordinary photogenic paper, I select, in the 
first place, paper of a good fijrm quality and smooth sm-face. I do 
not know that anything answers better than supei'fine wi'iting- 
paper. I dip it iuto a weak solution of common salt and wipe it 
dry, by which the salt is unifoi-mly distributed throughout its 
substance. I then S2:)read a solution of nitrate of silver on one 
surface only, and diy it at the fire. The solution should not 
be satui'ated, but six or eight times diluted with watei*. When 
dry, the paper is fit for use. 

" I have found by experiment that there is a certain propor- 
tion between the quantity of salt and that of the solution of 
silver which answers best, and gives the maximum effect. If 
the strength of the salt is augmented beyond this point, the 
efiect diminishes, and, in cei-tain cases, becomes exceedingly 

" This paper, if properly made, is veiy useful for aU photoge- 
nic pm-poses. For example, nothing can be more perfect than 
the images it gives of leaves and flowei's, especially with a sum- 
mer smi, — the light passing tlu'ough the leaves, delineates every 
ramification of their nerves. 

" Now, suppose we take a sheet thus pre})ared, and wash it with 
a saturated solution of salt, and then diy it. We shall find (es- 
pecially if the paper is kept some weeks befoi'e the trial is made) 
that its sensibility is greatly diminished, and, in some cases, 
seems quite extinct. But if it is again washed with a liberal 
quantity of the solution of silver, it becomes again sensible to 
light, and even more so than it was at first. In tliis way, by 
alternately washing the paper with salt and silver, and (hying it 
between times, I have succeeded in increasing its sensibility to 
the degree that is requisite for receiving the images of the ca- 
mera obscm'a. 

"In conducting this operation, it wUl be fovmd that the re- 
sults are sometimes more and sometimes less satisfactory in con- 
sequence of small and accidental variations in the proportions 
employed. It happens sometimes that the chloride of silver is 
disposed to darken of itself without any exposm-e to light : this 


shows that the attempt to give it sensibility has been canied too 
far. The object is to approach to this condition as near as pos- 
sible without reaching it, so that the substance may be in a state 
ready to yield to the slightest extraneous force, such as the 
feeble impact of the violet rays when much attenuated. Having, 
therefore, prepared a number of sheets of paper with chemical 
proportions sbghtly diiferent from one another, let a piece be 
cut from each, and, liaving been duly mai'ked or nimibered, let 
them be placed, side by side, in a very weak diffused light for a 
quarter of an hour. Then, if any one of them, as fr-equently hap- 
pens, exhibits a marked advantage over its competitoi-s, I select 
the jmper which beai's the corresponding number to be placed in 
the camera obsciu-a." 

The increased sensitiveness given to paper by alternate ablu- 
tions of saline and argentine washes, the striking diiferences of 
effect produced by accidental variations of the proportions in 
which the chemical ingi'edients are applied, and the spontaneous 
change which takes place, even in the dark, on the more sensitive 
varieties of the paper, are aU subjects of gi'eat intei'est, which 
demand fru'ther investigation than they have ever yet received, 
and which, if followed out, promise some most important expla- 
nations of chemical phenomena at present involved in uncer- 
tainty, particularly those which appear to show the influence of 
time, an element not sufficiently taken into account, in ovei'- 
coming the weaker affijiities. Few fields of research promise a 
gi-eater measiu'e of reward than these ; already the art of making 
sun-pictui-es has led to many very important physical discoveries, 
but most of the phenomena are yet involved in obscurity. 

Section II. — The Calotype. 

Although, in order of date, the investigations of Sfr John 
Hei-schel and others have a priority over those particular expe- 
riments of Mr. Talbot's which resulted in the discoveiy of his 
very beautiful process, the calotype, yet to avoid confusion, it is 
thought advisable to group together the discoveries of each in- 
vestigator, where thLs is practicable, in our historical division. 

The earUest productions of Mr. Talbot were simply such pre- 
parations as those already described, in which a chloride of silver 
was formed on the siu-face of the paper, with some nitrate of 
silver in excess. These need not be any fru'ther described than 
they have afready been. 

Eai-ly in 1810, di-awings on paper were handed about in the 
scientific cfrcles of London and of Paris, which were a great ad- 


vance upon anytMng which had been previously done. These 
were the residts of a new process discovered by Mr. Talbot, and 
then attracted so much attention, that INI. Biot made them the 
subject of a communication to the Academy of Sciences in Paris. 
His remarks are printed in extenso in the Coviptes Rendus, 
fi'om which the following passages ai'e translated, as they bear 
particularly on many of the defects which still continue to prove an- 
noyances in the photogi-ajihic process to which they have reference. 

Many of the remarks have a peculiar value fi'om the sugges- 
tions they contain, and they are worthy of record as marking 
the period when the French were first made acquainted with 
the i^i'ocesses on paper, as 23i'actised in England. Some dispo- 
sition has been shown on the part of several continental photo- 
graphers to claim originality for processes published in England 
many years before their o\m were devised, and which singularly 
resemble them. After remarking that many very important 
physical facts were being developed by the study of photogi-aphy, 
M. Biot continues : — 

"It is not to be expected that photogenic drawings, made on 
paper, can ever equal the clearness and fineness of those obtained 
on level and polished metallic plates. The texture of jmper, its 
superficial roughnesses, the dej)th of the imbibitions, and the 
capillaiy communication established between the various un- 
equally marked parts of its surface, are so many obstacles to 
absolute strictness of delineation, as well as to the regular 
gradation of tints in the camera obscura ; and the influence of 
these obstacles is greater when the chemical operation is slowly 
cari'ied on. But when there is no pretence or necessity for 
submitting to the delicacies of ai-t — when it is requii-ed, for 
example, to copy rare manuscripts faithfully — if we have jiapei-s 
which are very susceptible of receiving impressions in the cameiu 
obsciu-a, they will suffice perfectly ; particularly when they 
present, Kke those of Mr Talbot, the facility of immediately 
procuring copies of the primitive ch-awing. It will, therefore, 
doubtless be found more commodiou.s, and often even more 
practicable, to put four or five hundred dra^\-ings in a portfolio, 
than to carry about a similar pro'vision of metallic plates with 
tliose indispensable protectors, squares of glass, to cover them. 
Attempts are being made, at this time, to fix the images pro- 
duced by the Daguerreotype — perfect 2)rints, it is tme, but which 
are as light as the vapoxu- fi.-om which they are produced ; and, 
indeed, to bring a voluminous collection of these fragile products 
through the accidents incident to long, and sometimes perilous 
voyages, is a task requiring no ordinary care. But whoever has 
attentively studied the combination of physical conditions whence 


these admirable images result, will find it very difficidt — T am far 
from saying impossible — to fix them, 'without destroying, or at 
least without essentially altering, the causes which produce their 
charm ; and then, for the purposes which 1 have mentioned, 
jDapers very suscej^tible of impression would still have the advan- 
tages of being less troiiblesome in removal from place to place, 
as also of more easy presei'vation. 

" The utility of sensitive papers for copying texts was a natural 
consequence of the clearness of the copies of engi*avings which 
Mr. Talbot had ah-eady obtained by application, and which were 
presented to the Academy. He has inckided others among those 
just sent : there are also added specimens of this especial appli- 
cation, consisting of copies of a Hebrew psalm, of a Pei*sian 
Gazette, and of an old Latin chart of the year 1279. Our 
brethi'en of the AcoxUmie des £elles Lettres, to \^hom. I exhibited 
these impressions, were pleased to remai'k the fidelity of the 
charactei-s, and theii- clearness, by which they ai-e rendered as 
legible as the original text. Doubtless an old manuscript may 
be copied more C{uickly and more accui'ately by this means than 
by hand, even when the language in which it is written is 
undei*stood. However, we must stoj^ here. These copies are 
obtained by application : we must be enabled to obtain them by 
immediate radiation in the camera obsciu-a. It is the only 
means of extending the process to papyrus and other ojijaque 
manuscripts, or which are not snfficiently transparent for radia- 
tion to traverse them. Moreover, the application of leaves is 
very difiicult when they are bound up in a volume, and cannot 
be detached from one another. 

"But this important extension will require much physical per- 
fecting, towards which experunenters should direct their efibrts. 
The fii'st thing will be to augment the sensibility of the paper as 
much as possible, in order that the capillaiy communication of 
its various parts may not have sufiicient time to deteriorate the 
effects of the local and immediate action of the radiation. I 
should be led to believe that it is principally to this kind of 
commimication shoidd be attributed the fact remarked by Mr. 
Talbot, that, in experiments by application, it is more difficult 
to copy clearly a tissue of black lace spread on a w-hite ground, 
than w'hite lace on a black ground ; two cases of which he here 
gives examples. But another more liidden and more general 
difficiilty seems to me to proceed from the unequal faculty of 
vaiious substances for reflecting the radiations which strike 
them, and perhaps from then* aptitude for making them undergo 
physical modifications. For example, you wish to copy by radia- 
tion in the camera obscm-a a pictiu'e painted on canvas, wood, 


or porcelain : the different colonring substances employed by 
the painter are placed and distributed in sucli a manner that 
each of them absorbs certain portions of the total incidental light, 
and reflects especially towai'ds your eye the complementaiy por- 
tions, wherein predominate the rays proper to foi-m the tint 
of which it would give you the sensation. ■ But the chemically 
active reagent which the same pai-ts of the picture receive and 
reflect, is distinct from the light which affects your retina. In 
order that the chemical effect which it produces on the sensible 
paper, or on M. Daguen-e's layer of iodine, may present, in light 
or in shade, the equivalent of the colom-ed pai-ts, it is requisite 
— 1st, that this reflected radiation be chemically active ; 2d, 
that the energy of its action be proportional to the intensity of 
illumination operated in the eye by the portion of himinous 
radiation reflected fi-om the same point of the picture. Now this 
latter concordance certainly should not be fulfilled in an equal 
degree, by the varions coloiu'ing matters, which affect the eye in 
the same manner, and which the painter may substitute for one 
another in his work. Substances of the same tint may present, 
in the quantity, or the nature of the invisible radiations which 
they reflect, as many diversities, or diversities of the same order, 
as sxibstances of a different tint present relative to light : in- 
versely they may be similar in then- property of reflecting 
chemical radiations, when they are dissimilar to the eye : so that 
the differences of tint which they presented in the pictm-e made 
for the eye, will disappeai- in the chemical pictui-e, and will be 
confused in it in a shade, or of an imiibrm whiteness. These 
are the difficulties generally inherent in the formation of 
chemical pictm-es ; and they show, I think, evidently, the illu- 
sion of the experimenters who hope to reconcile, not only the 
intensity, but the tints of the chemical impressions produced 
by radiations, with the coloiu-s of the objects li-om which these 
radiations emanate. However, the distant or near relations of 
these two species of phenomena are veiy cm-ious to study, not 
only as regards the photogenic art, smce that name has, very 
improijerly, been given it, but likewise as regards experimental 
physics. I doubt not that examples of these peculiarities may be 
remarked in the images of natm-al objects and coloui'ed pictures 
executed by the Daguerreotype ; but veiy apparent ones may be 
seen among Mr. Talbot's present impressions. Thus, some of them 
represent white procelain vases, coloured shells, a candlestick (of 
metal) with its taper, a stand of white hyacinths. The whole of 
these objects ai-e felt and perceived veiy well in then- chemical 
image ; but the pai-ts which reflect the purely white light, probably 
also the radiations of eveiy kind, are, relatively to the othei-s, in 



an exaggerated proportion of iUiiniination, which, it seems to me, 
must result, paitially, from the capillaiy conmiunication diu-ing 
the continuance of the action ; so that the inequaKty would he 
less if the paper M-ere more sensitive or more rapidly acted on. 
In the hyacinth, the stalk and the green leaves have produced 
scarcely a faint trace of theii' configii ration ; hut they are strongly 
defined, especially in the parts of the outline, where more or less 
perfect speculai" reflection takes place. The points of the candle- 
stick (metallic), where this reflection occui-red, are copied by white 
stains locally applied, and which deteriorate the effect of the 
whole hy theii* disproportion. But tliis is seen especially in a 
pictiu-e by Correggio, the frame of which was veiy vividly copied, 
whilst the figiu-e on the canvas was hai-dly pei'ceptible. This 
disproportion of lustre in the reproduction of some white parts, 
especially when they ai-e dull and consequently veiy i-adiating, 
is sensible in certain pai-ts of views taken by Mr. Talbot, to the 
point of rendering dilficult the interpretation of the object to 
which they belong. However, these views are very satisfactory, 
as being obtained on paper, in the present season. Moreover, 
by an advantage pecidiar to the chemical preparation which ]\Ir, 
Talbot uses, it appeal's that the operations once completed, the 
di'awiugs ai-e no longer alterable by radiation, even acting with 
much energy. Indeed, we have here, as an example, four proofs 
of the same \^ew of INIr. Talbot's house, with an identical dispo- 
sition of lights and shades ; so that some, at least, if not thi-ee 
out of foiu', must have been procm-ed by superposition. Mr. 
Talbot is right in representing this property of reproduction as 
an especial advantage of his process, and it would indeed be very 
useful in voyages. I have exposed one of these di-awings to the 
action of the sun, not very powei-fid, it is tiiie, for several hours, 
and I have not perceived the slightest alteration in the lights. 
I think I understand that, in Mr. Talbot's opinion, the shades 
alone ai-e streng-thened xmder this influence. According to what 
I have just said, it should be expected that the trimnph of this 
process, as of every other photogenic reproduction, would take 
place with objects of white and dull plaster. Indeed, Mr. 
Talbot's parcel contains eight copies of busts and statues ; six 
of which chiefly, of various forms and sizes, present very remark- 
able results, especially taking into consideration the unfavoui-able 
season at which they were produced. Truly, there is not found 
in them the strict perfection of trace, nor the admirable grada- 
tions of lights and shades, which constitiite the charm of M. 
Daguen-e s impressions ; and I again repeat it, that my expres- 
sions may not be exaggerated. But I also repeat, that repre- 
sentations on sensitive papers must be considered as principally 


applicable to a different object, wliicli does not impose sucli 
strict conditions of art, reqiiii-iug only faithful images, siifficiently 
clear in tbeii' details to be readily recognized, and which, more- 
over, beiag obtained with rapidity, by an easy manipulation, may 
be kept with veiy little care, comprised in great number in a 
small compass, and moved from place to place with facility. ]\Ir. 
Talbot's papers abeady present many of these essential qualities, 
with the advantage of being able to fimiish niimerons copies 
immediately. His efforts, and those of others occupied with the 
same subject, will conclude by adding to them eveiy thing which 
may be desirable, provided that expectation, or the pretension 
of a perfection of art physically incompatible with operations on 
paper, do not give a false direction to their endeavour's. How- 
ever, not to appear to despair too much of the futm-e, I may add 
that the height of success would consist in discovering a sub- 
stance very susceptible of receiving impressions, which might be 
apphed on a papp-aceous leaf without penetrating deep into it, 
and which might, however, be fixed in it after the operation, as 
in Mr. Talbot's impressions. It does not seem necessaiy even 
that the fii'st impression thus rapidly obtained should copy the 
lights and shades in their proper jjlaces, provided that its trans- 
pai-ency and fixedness were such that we might deduce them 
from the application of copies whereia the invei'sion would be 
corrected. And perhaps, by this decomposition of the problem 
into two successive operations, one of the best ways is opened 
by which it may be resolved." 

Numerous improvements have been introduced, but still physi- 
cal difficulties, such as those which he has indicated, surroimd the 
photogi-aphic processes, and even where INI. Biot has proved 
"WTong in his conjectm^es, his remarks form a curious chapter in 
the histoiy of the art. 

Mr. Talbot's description of his process, the patent for which 
is dated 1841, is as follows : — * 

Take a sheet of the best writing-paper, having a smooth sur- 
face, and a close and even texture. The water-mark, if any, 
should be cut off, lest it should injure the appearance of the 
picture. Dissolve 100 gi-ains of crystallized nitrate of silver in 
six oimces of distilled water. "Wash the paper with this solution 
with a soft bnish on one side, and put a mark on that side, 
whereby to know it again. Diy the paper cautiously at a dis- 
tance fi'om the fii-e, or else let it diy spontaneously in a dark 

* Mr. Talbot, by a letter in the Times of Atigust 13, 1852, gives to the 
public the right of using any of his patents for any purpose not involving the 
production of portraits from the life. The letter is printed in the Appendix. 


room. When dry, or nearly so, dip it into a solution of iodide 
of potassium, containing 500 gi-aias of that salt dissolved in one 
pint of water, and let it stay two or three minutes in the sohi- 
tion. Then dip the paper into a vessel of water, diy it lightly 
with blotting-paper, and finish diying it at a fire, which will not 
injiu-e it even if held pretty near : or else it may be left to chy 
spontaneously. All this is best done in the evening by candle- 
light : the paper, so far prepared, is called iodized paper, because 
it has a uniform pale-yellow coating of iodide of silver. It is 
scai'cely sensitive to light, but nevertheless it ought to be kept 
in a portfolio or drawer until wanted for use. It may be kept 
for any length of time "without spoiling or undergoing any change, 
if protected from sunshine. When the paper is requii-ed for use, 
take a sheet of it, and wash it with a liquid pi-epai'ed in the 
following manner : — 

Dissolve 100 grains of crystallized nitrate of silver in two 
oimces of distilled water; add to this solution one-sixth of its 
volume of strong acetic acid. Let this be called mixtiu'e A. 

Make a saturated solution of crystallized gallic acid in cold 
distilled water. The quantity dissolved is veiy small Call this 
solution B. 

Mix together the liquids A and B in equal volumes, btit only 
a small quantity of them at a time, because the mixtm-e does not 
keep long without spoiling. This mixture ]Mr. Talbot calls the 
gallo-nitrate of silver. This solution must be washed over the 
iodized pajaer on the side marked, and being allowed to remain 
upon it for half a minute, it must be dij^ped into water, and then 
lightly dried with blotting-paper. This operation in particular 
requires the total exclusion of daylight ; and although the paper 
thus prepared, has been found to keep for two or tliree months, 
it is advisable to use it within a fcAv hoiu's, as it is often rendered 
useless by spontaneous change in the dark. 

Paper thu^s prepai-ed is exquisitely sensitive to light; an ex- 
posiu'e of less than a second to diffused daylight being quite 
sufficient to set up the process of change. If a piece of this 
paper is partly covered, and the other exposed to daylight for 
the briefest p)Ossihh period of time, a veiy decided impression 
will be made. This impression is latent and invisible. If, how- 
ever, the paper be placed aside in the dark, it will gi-adually 
devehpe itself; or it may be brought out immediately by being 
washed over with the gallo-nitrate of silver, and held at a short 
distance from the fii-e, by which the exposed portions become 
brown, the covered j^arts remaining of theii- original colour. The 
pictm-es being thus procured, are to be fixed by washing in clean 
water, and lightly di}-ing between blotting-paper, after which 


tliey ai'e to be washed over Tvdtli a solution of bromide of potas- 
sium, containing 100 graias of that salt, dissolved in eight or ten 
ounces of water ; after a minute or two, it is agaia to be cUpped 
into water, and then finally dried. 

Such was, ia aU its main features, the description given by 
Mr. Talbot in his specification of his process for producing the 
Calotype, or beautiful 2)icture (as the term sigiiifies) : he, in a 
second patent, included the points stated in the next section. 

Skctiox III. — Improvemknts IX Calotvpe. 

Such is the tenn employed by Mr. Talbot, and these im- 
provements consist of the follo^sdng particulai's, constituting that 
gentleman's second claim. 

1. Removing the yeUo^dsh tint which is occasioned by the 
iodide of silver, from the paper, by plvmging it into a hot bath of 
hyposulphite of soda dissolved in. ten times its weight of water, 
and heated nearly to the boiling point. The picture shoiild 
remain in the bath about ten minutes, and be then washed ia 
warm water and di'ied. 

Although this has been included by Mr. Talbot in his specifi- 
cation, he has clearly no claim to it, since, in Febiiiary 1840, Sir 
John Herschel published, in liis Memoir " On the Chemical 
Action of the Rays of the Solar Spectrum," a process of fixing 
with the hot hy[:)Osulpliite of soda. 

After undei-going the operation of fixing, the picture is placed 
upon a hot iron, and wax m.elted uito the pores of the paper to 
increase its transparency. 

2. The calotype paj)er is rendered more sensitive by placing 
a warm iron behind in the camei-a whilst the light is acting 
upon it. 

3. The preparation of io-gallic pfiper, which is simply washing 
a sheet of iodized paper with gaUic acid. In this state it will 
keep in a portfolio, and is rendered sensitive to light by washing 
it over with a solution of nitrate of silver. 

4. Iodized paper is washed with a mixture of twenty-six parts 
of a saturated solution of gallic acid to one pai-t of the solution 
of nitrate of silver ordinarily used. It can then be di'ied without 
fear of spoiling, may be kept a little time, and used without 
foi-ther preparation. 

5. The improvement of photogi-aphic dra^\'ings by exposing 
them twice the tisual time to the action of sunlight. The shadows 
are thus rendered too dark, and the lights are not sufliciently 
white. The di'awing is then wa.shed, and plunged into a bath of 


iodide of potassium, of tlie strengtli of 500 grains to each, piut 
of water, and allowed to remain in it for one or two minutes, 
wliicli makes tlie pictiu'es brigliter, and its lights assvune a pale- 
yellow tint. After tliis, it is washed, and immersed in a liot batli 
of liyposulphite of soda until tlie pale-yellow tint is removed, 
and the lights remain quite white. The pictures thus finished 
have a pleasing and peculiar effect. 

6. The appeai'ance of photograjihic pictures is improved by 
■waxing them, and placing white or coloiu'ed paper behind them, 

7. Enlarged copies of dagueiTeotypes and calotypes can be 
obtaiued by tlu'owing magnified images of them, by means of 
lenses, upon calotyjie pajaer. 

8. Photograjjhic printing. A few pages of letterpress are 
printed on one side only of a sheet of paper, which is waxed if 
thought necessary, and the letters are cut out and sorted ; then, 
in order to compose a new page, a sheet of white paper is ruled 
with straight lines, and the words are formed by cementing the 
separate letters in theii' proper order along the lines. A nega- 
tive photographic copy is then taken, having white letters on a 
black ground; this is fixed, and any number of positive copies 
can be obtained. Another method proposed by the patentee is 
to take a copy by the camera obsciu-a from large letters painted 
on a white board. 

9. Photographic publication. This claim of the patentee con- 
sists in making, first, good negative di-awings on papers prepared 
with salt and anmionio-nitrate of silver ; secondly, fixing them 
by the process above described ; thii-dly, the formation of positive 
di-awings from the negative copy, and fixing. 

These claims, taken from the specification as published in the 
Repertory of Patent Inventions, are preserved, in their original 
form, for the purpose of showing how much that is now fully 
accomplished was foreseen by Mr. Talbot as the result of his 

Section IY. — Pictures on Porcelain Tablets. 

A third patent has been obtained by Mr. Talbot, mainly in- 
volving the use of porcelain as a substitute for glass, and con- 
tains some useful facts noticed by Mr. Malone. 

The fii'st part of the patentee's invention consists in the use of 
plates of unglazed porcelain, to receive the photogTaphic image. 
A plate intended for photographic pm-poses should be made of the 
finest materials emjiloyed by the manufactiu-ers of porcelain ; it 
should also be flat, very thin, and semi-transparent ; if too thin, so 


that there would be a chance of breaking, it may be attached by- 
means of cement to a piece of glass, to give it strength. The sub- 
stance of the plate shotild be sUghtly porous, so as to enable it to 
imbibe and retaiu a sufficient quantity of the chemical solutions 
employed. To prepare the plate for use, it is fii-st required to give 
it a coating of albumen, or white of eggs, laid on veiy evenly, 
and then gently di'ied at a foe. According as the plate is more 
or less porous, it requires more or less of the albuminous coating ; 
it is best to employ a veiy close-gi'ained porcelain, which requii-es 
but little white of egg. The prepared plate may be made sensi- 
tive to light in the same way in which a sheet of paper is 
rendered sensitive ; .and we generally find the same methods ap- 
plicable for photographic pictiu"es on paper, applicable to those 
on porcelain plates, and one of the processes employed by the 
patentee is nearly the same as that patented by jNIr. Talbot in 
1841. The prepai'ed plate is dipped iato a solution of nitrate 
of silver, made by dissolving twenty-five gi-ains of nitrate in one 
ounce of water : or the sohition is spread over the plate uni- 
formly with a bi-ush; the plate is then di-ied, afterwards dipped 
into a solution of iodide of potassium, of the strength of about 
twenty-five gi-ains of iodide to one ounce of water, again dried, 
and the smface inibbed clean and smooth ^vith cotton. The 
plate is now of a pale-yellow coloiu", owing to the formation on 
its sm-face of iodide of silver. The plate, prepared as above 
directed, may be kept in this state vmtil required, when it is to 
be rendered sensitive to light by washing it over with a solution 
of gallo-nitrate of silver, then placed in the camera; and the image 
obtained is to be rendered visible, and sufficiently strengthened, 
by another washing of the same liquid, aided by gentle wai-mth. 
The negative pictui'e thus obtained is fixed by washing it with 
water, then with bromide of potassium, or, what is still better, 
h}qiosulphite of soda, and again several times in water. The 
plate of porcelain being semi-transparent, positive pictures can 
be obtained fi'om, the above-mentioned negative ones by copying 
them in a copying-frame. 

The pictm-e obtained on porcelain can be altered or modified 
in appeai*ance by the application of a strong heat, a process not 
applicable to pictiu*es taken on paper. "With respect to this part 
of their invention, the patentees claim : — " The obtaining by 
means of a camera, or copying-frame, photographic images or 
rictures upon slabs or plates of porcelain." The second part 
relates to the process which has been discovered and improved 
upon by INIr. Malone, who is associated vrith. Mr. Fox Talbot in 
the patent. The patentees' improvement is a method of ob- 
taining more complete fixation of photographic pictures on paper. 


For this purpose, tlie print, after vindergoing tlie iisual fixing 
process, is dipped into a boiling solution of strong caustic 
potash, which changes the colour of the print, and usually, after 
a certain time, acquii'es something of a gi-eenish tint, which 
indicates that the process is terminated. 

The picture is then well washed and dried, and if the tint ac- 
quii'ed by it ig not pleasing to the eye, a slight exposui'e to the 
vapoiu's of sulphiu'etted hydi'ogen will restore to it an agi-eeable 
brown or sepia tint. Under this treatment the pictiu'e dimi- 
nishes in size, insomuch that if it were previously cut in two, 
and one paiii submitted to the potash process, and the other 
not, the two halves, when affcei'wards put together, would be 
found not to correspond. The advantages of this process for re- 
moving any iodine which, even after fixing with the hyposulphite, 
remains in the paper, is gi'eat, and it will tend much to preserve 
these beautifid transcripts of natiu-e. 

The patentee also claims as an improvement the use of var- 
nished, or other transparent paper, impendous to water, as a 
substitute for glass, in certain circumstances, to support a film 
of albumen for photogTaphic pm'poses. A sheet of -wiiting-paper 
is brushed over with several coats of varnish on each side : it 
thus becomes extremely ti-ansparent. It is then brushed over on 
one side A\ albimien, or a mixture of albumen and gelatine, 
and diied. This film of albumen is capable of being rendered 
sensitive to light by exposing it to the vapour of iodine, and by 
following the rest of the process indicated in the preceding 
section of this specification. The advantages of using varnished 
or oil paper do not consist in any superiority of the images over 
those obtained upon glass, but in the gi-eater convenience of 
using paper than glass in cases where a large number of ijictures 
have to be made and can'ied about for considerable distances : 
besides this, there is a well-knowTi kind of photographic pictiu'es 
gi^-ing panoramic views of scenery, which are produced upon a 
curved sm-face by a movement of the object-glass of the camera. 
To the production of these images glass is hardly applicable, 
since it cannot be readily bent to the requii-ed cmwe and again 
sti-aightened ; but the case is met by emploj-ing talc, varnished 
paper, oiled paper, &c., instead of glass. It will be seen that 
the varnished paper acts as a support to the film of albiunen or 
gelatine, which is the surface on which the light acts, and forms 
the j^ictm-e. The next imi^rovement consists in forming photo- 
gi'aphic pictui'es or images on the siu'faces of polished steel plates. 
For this purpose, one pai-t (by measin-e), of a saturated solution 
of iodide of potassium is mixed with 200 parts of albumen, and 
spread as evenly as possible upon the sui-face of a steel plate 


and dried by the heat of a gentle fire. The plate is then taken, 
and, whilst still wann, is washed oyer with an alcoholic solution 
of gallo-nitrate of silver, of moderate strength. It then becomes 
very sensitive, and easily receives a photogi-aphic image. If the 
plate be cold, the sensibility is considerably lower. The image 
obtained is fixed by washing with h^-posiilphite of soda, and 
finally 's\'ith water. 

Section Y. — Instantaneous Process. 

The next invention and patent of Mr. Fox Talbot possesses 
many peculiarities, and as the results are of a remai-kable character, 
it is important that the px'ocess should be given uncurtailed in its 
main particvdai-s. The following description must be regarded 
as an absti-act of ]Mi'. Talbot's communication to the Atlienceum, 
Dec. 6, 1851. An expei-iment was tried in June, at the Royal 
Institution, in which an instantaneous image was produced; but 
as the process was the subject of another patent, it was not pub- 
lished \intil the above date. The expei-inient in question was 
that of obtaining a photogi-aphic copy of a printed paper fa.stened 
to a wheel, which was made to revolve as rapidly as possible, by 
illuminating it for a moment by the light obtained fi-om the 
discharge of a Leyden batteiy : the bill was faithfully printed, 
not even a letter being indistinct. 

A glass plate is employed, and Mr. Talbot thus directs that it 
should be prejDared. 

1. Take the most liquid portion of the white of an egg, yq- 
jecting the rest. Mix it with an equal quantity of water. Spread 
it veiy evenly upon a plate of glass, and diy it at the fire. A 
strong heat may be used without injuring the plate. The film 
of dried albumen ought to be unifonn and nearly invisible. 

2. To an aqueous solution of nitrate of silver add a conside- 
rable quantity of alcohol, so that an ounce of the mixtiu'e may 
contain three gi-ains of the nitrate. I have tried various pro- 
portions, fi-om one to six gi-ains, but perhaps thi'ee gi-ains answer 
best. More experiments are here requii'ed, since the results 
are much influenced by this part of the process. 

3. Dip the plate into this solution, and then let it dry spon- 
taneously. Faint prismatic colom-s will then be seen upon the 
plate. It is important to remark, that the nitrate of silver 
appeal's to form a tiiie chemical combination with the albumen, 
rendering it much harder, and insoluble in liqiuds which dis- 
solved it previously. 

4. Wash with distilled water to remove any superfluous por- 
tion of the nitrate of silver. Then give the plate a second 


coating of albumen similar to the fii'st, but, in diying, avoid 
heating it too much, which would cause a commencement of 
decomposition of the silver. 

5. To an aqueous solution of proto-iodide of ii'on add, first, an 
equal volimie of acetic acid, and then ten volumes of alcohol. 
Allow the mixture to I'epose two or thi'ee days. At the end of 
that time it ^vi)l have changed coloiu-, and the odoiu- of acetic 
acid as well as that of alcohol ^\'ill have disappeared, and the 
liquid will have acquired a peculiar but agreeable vinous odour. 
It is in this state that I prefer to employ it. 

6. Into the iodide thus prepared and modified, the plate is 
dipped for a few seconds. AH these operations may be per- 
formed by moderate daylight, avoiding, however, the direct solar 

7. A solution is made of nitrate of silver, containing about 
70 grains to one ounce of water. To thi-ee pai-ts of this add two 
of acetic acid. Then, if the prepared plate is rapidly dipped 
once or twT.ce into this solution, it acqiiii-es a \qyj great degree 
of sensibility, and it ought then to be placed in the camera 
without much delay. 

8. The plate is withch-awn from the camera, and in order to 
bring out the image, it is dipped iuto a solution of pi'otosvdphate 
of iron, containing one pai-t of the satiu-ated solution diluted 
with two or thi-ee parts of water. The image appeal's very 

9. Having washed the plate with water, it is now placed in a 
solution of hyposulphite of soda, which in one minute causes the 
image to brighten up exceedingly, by remo\Tng a kind of veil 
which previously covered it. 

10. The plate is then washed with distilled water, and the 
process is terminated. In order, however, to guard against 
futiu'e accidents, it is well to give the picture another coating of 
albumen and of varnish. 

" These operations may appear long in the description, but 
they are rapidly enough executed after a little practice. In the 
process which I have now described, I trust that I have effected 
a harmonious combination of several previously ascertained and 
valuable facts, esj^eciaUi/ of the 2)hotographic 2^ropert^ of iodide 
of iron, which ivas discovered hy Dr. Woods, of Parsonstown, 
in Ireland ; and that of sidphate of iron, for ivhich science is 
indebted to the researches of Mr. Robert Hunt. In the time 
adjustment of the proportions, and in the mode of operation, 
lies the diflBculty of these investigations, since it is possible, by 
adopting other ^jroportions and manipulations not very gi-eatly 
difiering from the above, and which a careless reader might 

Talbot's instantaneous process. 33 

consider to be the same, not only to fail in obtaining the highly 
exalted sensibility which is desirable in this process, but actually 
to obtain scarcely any photographic result at all." 

JVIr. Talbot proposed the name of Amplntype, or doubtful 
image, for these pictiu'es. This name had, however, been adopted 
previously, at INIr. Talbot's recommendation, by Sir John Her- 
schel, and in the Collodion processes, to be by-and-by described, 
we have similar phenomena, to which the name applies with 
equal force. 

It is not improbable but the high degree of sensibility which 
is certainly obtained in this process, is rather due to the forma- 
tion of an iodide of ethyle in the mixtiu'e, than to the combination, 
as INIi'. Talbot supposes, of the proto-iodide and the proto-sulphate 
of iron. My own researches convince me that we should seek 
for the highest degrees of sensibility amidst the numerous com- 
binations of the ethyle and methyle compounds with the metallic 

The last invention of Mr. Fox Talbot is one by which he 
obtains etchings of objects ; the images of which are produced 
by radiant action upon steel plates. This process, and analogous 
ones by others, will be described in Part III. 



Section I. — The Original Process of Daguerre, 

It has been already stated that Niepce and Daguerre having 
by accident discovered they were prosecuting experiments of the 
same kind, entered into a pai'tnership. On the 5th Dec, 1829, 
Niepce communicated to Daguerre the particulars of the process 
employed by him, which has been already described (Chap. II.), 
under the term Heliograph y. Niepce died in July 1833, but 
he has left some letters which clearly show that he had been a 
most industrious investigator. One extract appears of particular 
importance : — " I repeat it, sir," he says, " I do not see that we 
can hope to derive any advantage fi-om this process {the use of 
iodine^ more than from any other method which depends upon 
the use of metallic oxides," &c. Again, he says, " a decoction of 
Thlaspi (Shepherd's purse), fumes of phosphonis, and particularly 
of sulphur, as acting on silver in the same way as iodine, and 
caloric, produce the same effects by oxidizing the metal, for from 
this cause proceeded in all these instances theii" extreme sensibility 
to light." After the death of M. Nicephore Niepce, a new 
agreement was entered into between his son M. Isidore Niepce 
and Daguerre, that they should pm-sue their investigations in 
common, and shai-e the profits, whatever they might eventually 
prove to be. 

The discovery of DagueiTe was reported to the world early in 
January, 1839 ; but the process by which his beaxitiful jjictiu'es 
were produced was not made known until the July following, 
after a bill was passed securing to himself a pension for life 
of 6000 francs, and to M. Isidore Niepce, the son of M. Niepce 
above mentioned, a pension for life of 4:000 francs, with one-half 
ill reversion to their widows. It was regi-etted, that after the 
French Government had thus liberally purchased the secret of 
the process of the Daguerreotype, for "the glory of endoimng the 
world of science and of art loith one of the most surprising 


discoveries that honour tJieir tiative land," on the argiiment that 
" the invention did not admit of being secured by patent, for as 
soon as published all might avail themselves of its advantages,'' 
that its author shoiild have guarded it by a patent right in 

From the primaiy importance of this very beautiful branch of 
the photogi'aphic aii;, I shall devote some space to a description 
of the original process, reserving for the division devoted to the 
manipxilatory details the descrij)tion of each improvement which 
has been published, having any practical advantage, either by 
lessening the labour- required, or reducing the expense. 

The pictm-es of the daguerreotype are executed upon thin 
sheets of silver plated on copper. Although the copper serves 
principally to supj)ort the silver foil, the combination of the two 
metals appears to tend to the perfection of the effect. It is 
essential that the silver should be veiy pure. The thickness of 
the copper should be sufficient to maintain perfect flatness, and 
a smooth sm-face ; so that the images may not be distox-ted by 
any wai-ping or xmevenness. Unnecessary thickness is to be 
avoided on account of the weight. 

The process is di\'ided by DagueiTC into five oj^erations. The 
first consists in cleaning and polishing the plate, to fit it for 
receiving the sensitive coating on which light foi-ms the picture. 
The second is the formation of the sensitive ioduret of silver over 
the face of the tablet. The thii'd is the adju.sting of the plate in 
the camera obscura, for the purpose of receiving the impression. 
The foui-th is the bruiging out of the photographic picture, which 
is invisible when the plate is taken fi-om the camei-a. The fifth 
and last operation is to remove the sensitive coating, and thus 
prevent that susceptibility of change under luminous influence, 
which would othei'^\'ise exist, and quickly destroy the pictiu-e. 

First Operation.— A small i^hial of olive-oil — some finely 
carded cotton — a muslin bag of finely le-vigated pvunice — a i^hial 
< .f nitric acid, diluted in the proporfion of one part of acid to 

xteen parts of water, are reqxiired for this operation. The 
-ei-ator must also provide himself Av-ith a small spii'it-lamp, and 
au iron wire fi'ame, upon which the plate is to be placed whilst 
leuig heated over the lamj). The following figm-es represent 
iliis fi-ame. The first view is as seen fiom above. The second 
is a section and elevation, showing the manner in which it is 

The plate being first powdered over with piunice, by shaking 
the bag, a piece of cotton dipped into the olive-oil is then 
carefully nibbed over it with a continxious cii-cular motion, com- 
mencing from the centre. When the plate is well polished 



it must be cleaned by powdering it all over ^vitll piunice, 
and then rubbing it witli diy cotton, always ronndiiig and 
crossing the strokes, it being 
impossible to obtain a true 
siu'face by any other motion 
of the hand. The surface of 
the plate is now nibbed all 
over with a pledget of cotton, 
slightly wetted with the di- 
luted nitric acid. Frequently 
change the cotton, and keep 
rubbing briskly, that the acid 
may be equally diffused over 
the silver, as, if it is permitted 
to iTin into di-ops, it stains the 
table. It will be seen when 
the acid has been properly 
diffiised, from the appearance 
of a thin film equally spread over the surface. It is then to be 
cleaned off with, a little pimiice and diy cotton. 

The plate is now placed on the wire fi"ame — the silver upwards, 
and the spirit-lamp held in the hand, and moved about below it, 
so that the flame plays upon the copper. This is continued for 
five minutes, when a wliite coating is formed all over the sm-face 
of the silver; the lamp is then withdi'a%vn. A charcoal fii'e may 
be used instead of the lamp. The plate is now cooled suddenly, 
by placing it on a mass of metal, or a stone floor. When per- 
fectly cold, it is again polished A\dth chy cotton and pumice. It 
is necessary that acid be again applied two or three times, in 
the manner before dii-ected, the diy pumice being powdered over 
the plate each time, and polished off gently Tvath diy cotton. 
Care must be taken not to breathe upon the plate, or touch it 
with the fingers, for the slightest stain upon the sui-face ^\t11 be 
a defect in the drawing. It is indispen- 
sable that the last operation with the acid 
be performed immediately before it is in- 
tended for use. Let every pai-ticle of dust 
be removed, by cleaning all the edges, and 
the back also, with cotton. After the fii'st 
polishing, the plate c is fixed on a board 
by means of fom- fillets, b B B B, of plated 
copper. To each of these are soldered two a u o d 
small projecting pieces, which hold the ^• 

tablet near the corners ; and the whole is retained in a proper 
position by means of screws, as represented at D D d d. 




Second Operation. — It is necessary for this opex-ation, wliich. 
is really the most important of all, that a box, similar to figs. 4 

and 5, be provided. Figiu-e 4 
represents a section, supposed 
to pass do"\\Ti the middle of the 
appai'atus by the line A b in 
fig. 5, which represents the box 
as seen fi-om above, c is a small 
lid which acciu'ately fits the in- 
terior, and divides the boxes into 
two chambei's. It is kept con- 
stantly in its place when the 
box is not in use ; the piu'pose 
of it being to concentrate the 
vapoui' of the iodine, that it may 
act more readily upon the plate 
^ when it is exjwsed to it. d is 

the little capside in which 
the iodine is placed, which is covered mth the ring, J, upon 
which is stretched a piece of fine gauze, by which the particles 

of iodine are prevented 
ft'om rising and staining 
the plate, while the va- 
poiu", of coiu-se, passes 
treely through it. E is 
-B the board with the plate 
attached, which rests on 
the four smaller pro- 
jecting pieces, F, fig. 5. 
G is the lid of the box, 
which is kept closed, ex- 
cept when the plate is 
removed or inserted. H represents the supports for the cover c. 
K, tapei-ing sides aU roimd, forming a fimnel-shaped box within. 
To prepare the plate : — The cover c, being taken out, the cup, 
D, is charged with a sufficient quantity of iodine, broken into 
small pieces, and covered -with, the gauze, J. The board, E, is 
now, with the plate attached, placed feice dowTiwai-ds, in its pro- 
per position, and the box carefully closed. 

In this position the plate remains \mtil the vapour of the 
iodine has produced a definite golden yeUow coloui-, nothing 
more nor less.* If the operation is prolonged beyond the point 
at which this efiect is produced, a \-iolet coloiu- is assumed, 

* If a piece of iodine is placed on a silver tablet, it will speedily be sur- 
rounded with coloured rings: these being the colours of thin films, as described 

A — 



"which, is much less sensitive to light ; and if the yellow coating 
is too pale, the picture produced will prove very faint in all its 
parts. The time for this cannot be fixed, as it depends entirely 
on the tem^ieratiu-e of the surrounding air. No artificial heat 
must be applied, unless in the case of elevating the temperature 
of an apartment in which the operation. may be going on. It is 
also important that the temperature of the inside of the box 
should be the same as it is without, as otherwise a deposition of 
moisture is liable to take place over the surface of the plate. It 
is well to leave a portion of iodine always in the box ; for, as it is 
slowly vaporized, it is absorbed by the wood, and when required 
it is given out over the more extended surface more equally, and 
with greater i-apidity. 

As, according to the season of the year, the time for pro- 
ducing the requii-ed efiect may vary from five minutes to half 
an hour, or more, it is necessary, from time to time, to inspect 
the plate. This is also necessary, to see if the iodine is acting 
equally on every part of the silver, as it sometimes happens that 
the colour is sooner produced on one side than on the other, 
and the plate, when such is the case, must be tm-ned one quarter 
round. The plate must be inspected in a darkened room, to 
which a faint light is admitted in some indirect way, as by a 
door a little open. The board being lifted from the box "with 
both hands, the operator tvmiing the jJate towards him rapidly, 
observes the colour. If too pale, it must be retui-ned to the 
box ; but if it has assiuned the "violet colour it i« useless, and the 
whole process must be agaia gone thi'ough. 

From description, this operation may appear veiy difficult ; 

but with a Kttle practice the precise interval necessary to pro- 
duce the best effect is pretty easily guessed at. When the 

by Sir Isaac Newton. Close examination will show the formation of two yellow 
ringSi one within and the other without the series. If we cover one-half of the 
circle with a card, and expose the other part to light, the rings will be found to 
change colour, the outer and the inner yellow darkening the most readily, and 
to an equal shade ; thus proving the advantage of obtaining this yellow tone. 



proper yellow coloiu- is produced, tlie plate must be put into a 
fi-ame, whicli fits the camera obsciu-a, and tlie doors are instantly 
closed upon it, to j^revent the access of light. The figiu-es 
represent this fi-ame, fig. G, with the dooi"s, B B, closed on the 
plate ; and fig. 7, with the dooi-s opened by the half cii'cles, A a. 
D D are stops by which the doors ai-e fastened until the mo- 
ment when the plate is requii-ed for use. The thii'd operation 
should, if possible, immediately succeed the second : the longest 
interval between them should not exceed an hoxir, as the iodine 
and silver lose their requisite photogenic properties.* It is 
necessary to observe, that the iodine ought never to be touched 
with the fingers, as we are very liable to injure the plate by 
touching it with the hands thus stained. 

TMrd Operation. — The thii-d operation is the fixing of the 
plate at the jH-oper focal distance from the lens of the camera 
obscura, and placing the camera itself in the right position for 
taking the view we desii-e. Fig. 8 is a perpendicular section, 
lengthwise, of DagueiTe's camera. A is a gi-oimd glass by which 

the focus is adjusted ; it is then removed, and the photographic 
plate substituted, as in c, fig. 9. b is a mirror for observing 
the efiects of objects, and selecting the best points of view. 
It is inclined at an angle of io^, by means of the support, L. 
To adjust the focus, the mirror is lowered, and the piece of 
gi'ound glass, A, used. The focus is easily adjiisted by shding 
the box, D, out or in, as represented in the plate. When the 
focus is adjusted, it is retained in its place by means of the screw, 
H. The object glass, j, is achromatic and peiiscopic ; its diameter 
is about one inch, and its focal distance rather more than four- 
teen inches, m, is a stop a short distance fi'om the lens, the 

* This is contrary to the experience of the author of this volume ; and 
Dr. Draper, of New York, states that he has found the plates improve by 
keeping a few hours before they are used ; and M. Claudet states, that even 
after a day or two the sensibility of the plates is not impaired. 



object of which is to cut oS all those rays of light which do not 
come dii-ectly from the object to which the camera is du-ected. 
This instrument reverses the objects; that which is to the right 
in natm-e being to the left in the photograph. This can be 
remedied by using a mirror outside, as K J, in figure 9. This 
aiTangement, however, reduces the quantity of light, and in- 
creases the time of the operation one-third. It will, of course, 
be adopted only when there is time to spare. After having 
placed the camera in front of the landscape, or any object of 
which we desire the representation, our first attention must be 
to adjust the plate at such a distance from the lens, that a neat 
and sharply defined picture is 
produced. This is, of course, 
done by the obscured glass. The 
adjustment being satisfactorily 
made, the glass is removed, and 
its place sujDplied by the frame 
containing the prepared plate, and 
the whole secui-ed by the screws. 
The doors are now opened by 
means of the half ch-cles, and the 
plate exposed to receive the pic- 
ture. The length of time neces- 
sary for the production of the best 
efifect, varying with the quantity 
of light, is a matter which re- 
quires the exercise of considerable 
judgment, particularly as no im- 
pression is visible upon the tablet 
when it is withdrawn fr-om the 
camera. At Paris this varies from 
three to thirty minutes. The most 
favourable time is from seven to ^" 

three o'clock. A di-awing which, in the months of June and 
July, may be taken in three or four minutes, will require five or 
six in May or August, seven or eight in April and September, 
and so on, according to the season. Objects in shadow, even 
dui'ing the brightest weather, will require twenty minutes to be 
correctly delineated. From what has been stated, it will be 
evident that it is impossible to fix, with any precision, the exact 
length of time necessary to obtain photographic designs ; but by 
practice we soon learn to calculate the requii-ed time with con- 
siderable correctness. The latitude is, of coiu-se, a fixed element 
in this calculation. In the sunny climes of Italy and southern 
France, these designs may be obtained much more promptly 



than in tlie uncertain clime of Great Britain. It is very im- 
portant that tlie time necessary is not exceeded, — prolonged 
solarization has the effect of blackening the plate, and this de- 
stroys the clearness of the design. If the operator has failed in 
his fii'st experiment, let him immediately commence with 
another plate ; coiTecting the second trial by the fii'st, he will 
seldom fail to produce a good photogTaph. 

Fourth Operation. — The apparatus requii-ed ia this operation 
is represented by fig. 10. A, is the lid of the box ; B, a black 
board with grooves to receive the plate ; c, cup contaiaing a 
little mercmy, j; D, spu'it-lampj F, thermometer; G, glass 
through which to inspect the oj^eration ; H, tablet as removed 

from the camera ; i, stand for 
the spirit-lamp. All the in- 
terior of this apparatus shoxild 
be covered with hard black 
vamish. The board and the 
affixed plate being withdi-awn 
from the camera, are placed at 
an angle of about 45*^ within 
this box — the tablet with the 
pictm-e downwards, so that it 
may be seen thi'ough the glass 
G. The box being carefully 
closed, the spirit-lamp is to be 
lighted and placed under the 
cup containing the mercury. 
The heat is to be applied until 
the thermometer, the bulb of 
which is covered with the mer- 
cury, indicates a temperature 
of 60° centigrade (140'" Fah.) 
The lamp is then withdi-awn, 
and if the thermometer has 
risen rapidly, it will continue 
to rise without the aid of the lamp; but the elevation ought 
not to be allowed to exceed 75° cent. (167'' Fah.) 

After a few minutes, the image of nature impressed, but till 
now invisible, on the plate, begins to appear ; the operator 
assui-es himself of the progress of this development by examin- 
ing the picture thi-ough the glass, G, by a taper, taking care that 
the rays do not fall too strongly on the plate, and injm-e the 
nascent images. The operation is continued till the ther- 
mometer sinks to i5° cent. (113*^ Fah.) When the objects 




have been strongly illunimated, or when the plate has been kept 

in the camera too long, it will be found that this operation is 

completed before the thermometer has fallen to 

55'^ cent. (131'"'' Fah.) This is, however, always 

known by obsendng the sketch thi-ough the 


After each operation the apparatus is care- 
fully cleaned in every part, and in particidar the 
strips of metal which hold the plate are well 
rubbed with pumice and water, to remove the 
adhering mercury and iodiue. The plate may 
now be deposited in the grooved box (fig. 11), 
in which it may be kept, excluded from the light, 
until it is convenient to perform the last fixing 

Fifth Operation. — This process has for its object the removal 
of the iodine from the plate of silver, which prevents the fm-ther 
action of the light. 

A satui-ated solution of common salt may be used for this 
piu'pose, but it does not answer nearly so well as a weak solu- 
tion of the hyposulphite of soda. In the fii'st place, the plate is 
to be placed in a trough of watei-, plungmg and withdi-awing it 
immediately ; it is then to be plunged into one of the above 
saline solutions, which wovdd act upon the di^awing if it was not 
previously hardened by washing in water. 

To assist the effect of the saline washes, the plate must be 
moved to and 6-o, which is best done by passing a wu-e beneath 
the plate. When the yeUow colour has quite disappeared, the 
plate is lifted out, great care being taken that the impression is 
not touched, and it ls again plunged into water. A vessel of 
warm distilled water, or very pure rain-water boiled and cooled, 
being provided, the plate is fi:xed on an inclined plane, and the 
water is poiu'ed in a continuous stream over the picture. The 
drops of water which may remain upon the plate must be re- 
moved by forcibly blowing upon it, for otherwise, in diying, they 
would leave stains on the drawings. This finishes the di-awing, 
and it only remains to presei-ve the silver from tarnishing and 
from dust. 

The shadows in the Daguerreotype pictiu'es are represented 
by the polished svirface of the silver, and the lights by the ad- 
hering mercury, which will not bear the slightest rubbing. To 
preserve these sketches, they must be placed in cases of paste- 
board, with a glass over them, and then framed in wood, They 
are now unalterable by the sun's light. 


The same plate may be employed for many successive trials, 
provided the silver be not polished through to the copper. It 
is very important, after each trial, that the mercury be removed 
immediately by polishing with pumice-powder and oil. If this 
be neglected, the mercmy finally adheres to the silver, and good 
drawings caimot be obtained if this amalgam is present. 

Section II. — Improvements in Daguerreotype. 

It was announced that the inventor of the Daguerreotype had 
succeeded in improving the sensibility of his plates to such an 
extent, as to render an instantaneous expostire sufficient for the 
production of the best effects ; consequently, seciu-ing faithful 
impressions of moving objects. In a communication with which 
I was favoiu'ed from M. Daguerre, he said, — " Though the 
principle of my new discovery is certain, I am detennined not 
to publish it before I have succeeded in making the execution 
of it as easy to eveiybody as it is to myself I have annoimced 
it immediately at the Royal Academy of Paris, merely to take 
date, and to ascertain my right to the priority of the invention. 
By means of that new process, it shall be possible to fix the 
images of objects in motion, such as 2^uhliG ceremonies, market- 
places covered with 2^^02)le, cattle, dx. — the effect being instan- 

In 1844, M. Daguerre, in a letter to M. Arago, published this 
process ; but it proved so complex in its manipulatory details, 
and so veiy uncertain, that it has not been adopted. As it is, 
however, c\u'ious, and involves the use of some agents not ordi- 
narily employed, it is thought advisable to make some extracts 
from the Coniptes Rendus for April, 1844, in which it was pub- 
lished : — 

" By superposing on the plate several metals, reducing them 
to powder by friction, and by acidulating the empty spaces 
which the molecules leave, I have been enabled to develope 
galvanic actions which permit the employment of a much thicker 
layer of iodide, without ha\'ing to fear, diu-ing the oj^eration of 
light in the camera obscm-a, the influence of the liberated 

" The new combination which I employ, and which is com- 
posed of several metallic iodides, has the advantage of gi"ving a 
sensible layer capable of receiving impressions simultaneously 
by aU the degrees of tone, and I thus obtain, in a very short 
space of time, the representation of objects vividly enlightened 
with demi-tints, all of which retain, as in natiu'e, their ti'ans- 
parency and their relative value. 


"By adding gold to tlie metals wliicli I fii'st used, I am enabled 
to avoid the great difficulty which the use of bromine, as an 
accelerating substance, presented. It is known that only very 
experienced persons could employ bromine with success, and that 
they were able to obtaiu the maximtim of sensibility only by 
chance, since it is impossible to determine this point very pre- 
cisely, and since immediately beyond it the bromine attacks the 
silver, and is opposed to the formation of the image. 

" With my new means, the layer of iodine is always satui-ated 
with bromine, since the plate may, without inconvenience, be 
left exposed to the vapoiu- of this substance for at least half the 
necessary time ; for the aj^plication of the layer of gold is op- 
posed to the formation of what is called the veil of bromine. 
The process which I am about to give may, perhaps, be found 
rather complicated; but, notwithstanding my desire to simplify 
it as much as possible, I have been led, on the contrary, by the 
results of my experiment, to multiply the substances employed, 
all of which play an important pai-t in the whole jDrocess. I 
regard them all as necessary for obtaining a complete result, 
which must be the case, since I have only gradually arrived at 
discovering the properties of these different metals, one of 
which aids in promptitude, the other in the vigoiu- of the im- 
pression, &c. 

" The operation is divided into two principal parts : the first, 
which is the longest, may be made a long time previously, and 
may be regarded as the completion of the manufacture of the 
plate. This operation, being once made, serves indefinitely ; and, 
without recommencing it, a great number of impressions may be 
made on the same plate. The new substances employed are : — 
Aqueous solution of bichloride of mercury : solution of cyanide 
of mercury : white oil of petroleum, acidulated with nitric acid : 
solution of chlorine of gold and platinum. These are prepared 
as follows : — 

"Aqueous Solution of Bichloride of Mercury. — 8 grains of 
bichloride of mercury in 10,000 grains of distilled water. 

'• Solution of Cyanide of Mercury. — A flask of distilled water 
is satm-ated with cyanide of mercmy, and a certain quantity is 
decanted, which is diluted mth an equal quantity of distilled 

"Acidulated White Oil of Petroleum.*— This oU is acidulated 
by mixing with it one-tenth of pure nitric acid, leaving it for at 

* The most suitable oil of petroleum is of a greenish yellow tint, and takes, 
at different angles, azure reflections. 

I have given the preference to this oil over the fixed oils, because it always 
remains limpid, although strongly acidulated. My object in employing an 


least forty-eight haul's, occasionally agitating the flask. The oil 
which is acidulated, aud which then powerfully reddens litmus- 
paper, is decanted. It is also a little coloured, but remains veiy 

" Solution of Chloride of Gold and Platinnm.— In order not to 
multiply the solutions, I take the ordinaiy chloride of gold, used 
for fixing the impressions, and which is composed of 15 grains of 
chloride of gold, and 50 graias of h\-posulphite of soda, to a 
quart of distUled water. With respect to chloride of platinimi, 
4 grains must be dissolved in 3 quarts of distilled water ; these 
two solutions are mixed in equal quantities. 

" First Preparation of the Plate. — For the sake of brevity 
in the following description, I wiM abiidge the name of each 
substance. Thus, I will say, to designate the aqueous solution 
of bichloride of mercuiy, sublimate; for the solution of cyanide 
of mercury, cyanide; for the acidulated oil of petroleum, oil; for 
the solution of chloride of gold and platinum, gold and platinum ; 
and for the oxide of ii-on, ro^|,ge only. 

"The plate is first polished with sublimate and tripoli, and 
afterwards with rouge, until a beautiful black is arrived at. 
Then, the plate is laid on the hoiizontal plate, and the solution 
of cyanide is poured on it and heated over a lamp, as in fixing an 
impression with chloride of gold. The mercury is deposited, and 
forms a whitish layer. The plate is allowed to cool a Kttle, and, 
after having poured off the liquid, it is dried by rubbing with 
cotton and sprinkling with rouge. 

" It is now necessary to polish the whitish layer deposited by 
the merciuy. With a piece of cotton steeped in oil and rouge 
this layer is rubbed until it becomes of a fine black. In the last 
place, it may be rubbed veiy strongly, but with cotton alone, in 
order to render the acidulated layer as thin as possible. The 
plate is afterwards placed on the horizontal plane, and the solu- 
tion of gold and platinum is poiu'ed on. It is heated in the 
ordinary manner ; it is then allowed to cool, the liquid is poured 
off, and it is dried by gentle friction with cotton and rouge. 
This operation must be performed Tvdth care, especially when the 
impression is not immediately continued ; for, othei'WTise, some 
lines of liquid would be left on the plate, which it is cUfiicult to 
get rid o£ After this last friction the plates shoidd be only 

acidulated oil is to reduce the metals to powder, and to retain this powder on 
the surface of the plate, at the same time giving greater thickness to the layer 
by its unctuous properties ; for the naphtha which results from the distillation 
of this oil does not produce the same effect, because, being too fluid, it carries 
away the powder of the metals. It is for the same reason that I have lately 
recommended the employment of essence of lavender rather than that of essence 
of turpentine. 


dried, aud not polislied. This includes the fii'st preparation of 
the plate, which may be made a long time previously. 

"Second Preparation. — I do not think it fit to allow a longer 
interval than twelve hours to intervene bv2tween this operation 
and iodizing the plate. We left the plate with a deposit of gold 
and platinum. In order to polish this metallic layer, the plate 
is rubbed with a piece of cotton, and oil and rouge, xxntiL it again 
becomes black ; and then with alcohol and cotton only, in order 
to remove tliis layer of rouge as much as possible. The plate is 
again iiibbed very strongly, and passing several times over the 
same places, with cotton impregTiated with cyanide. As this 
layer ch'ies veiy j^romptly, it might leave on the plate traces of 
inequality; in order to avoid tliis, the cyanide must be again 
passed over it, and, while the plate is still moist, we quickly iiib 
over the whole sm-face of the plate with cotton imbibed with a 
little oil, thus mixing these two substances; then, with a piece 
of dry cotton, we nib, in order to unite, and, at the same, to dry 
the plate, taking cai-e to remove from the cotton the parts which 
are moistened with cyanide and oil. Finally, as the cotton stdl 
leaves traces, the plate is likewise sprinkled with a little rouge, 
which is removed by gently iiibbing. 

"Afterwards the plate is again rubbed with cotton impreg- 
nated with oil, only in such a manner as to make the bui-nish of 
the metal return ; it is then sprinkled -^ith rouge, and then very 
gently rubbed roimd, to remove all the rouge, which carries 
with it the superabundance of the acidulated layer.* Finally, 
it is strongly nibbed with a rather fii*m pledget of cotton, in 
order to give the last polish, t 

" It is not necessary often to renew the pledgets of cotton im- 
bibed with oil and rouge; they must only be kept free from 

" On Iodizing'. — The colour of the impression depends on the 
tint given to the metallic iodide; it may, therefore, be varied at 
will. However, I have foimd the \iolet rose colom" most suit- 

" For transmitting the iodine to the plate, the sheet of card- 
board may be replaced by an earthenware plate deprived of 
enamel. The iodine transmitted by this means is not decom- 

* This must be done as gently as possible ; for otherwise the rouge would 
adhere to the plate, and would form a general film. 

f In operating on a plate a long time after it has received the first prepara- 
tion, it is necessary, before employing the acidulated oil and red oxide, to mani- 
pulate, as I indicate further on, for the plate which has received a fixed impres- 
sion. This precaution is necessary for destroying the stains which time may 
have developed. 


posed. It is useless, I may even say injurious, to heat tlie plate 
before exposing it to the vapoiu' of iodine. 

"WasMng with Hyposulphite of Soda.— In order to remove 
the sensitive layer, the solution of hyjDosiJphite of soda must not 
be too strong, because it destroys the shai'pness of the impres- 
sion. 60 gi-ammes of the hyposulphite are sufficient for 1 quart 
of distilled water." 

The elaborate nature of this process is a baiTier against its 
use, since the residts are rarely equal to those obtained by the 
ordinary Dagiierreotype, as it is now practised, and the laboxu- to 
be expended on the preparation infinitely greater. 

The advantages which have been derived from the employ- 
ment of compounds of iodine and bromine, or chlorine, by which 
the sensibility of the DagueiTeotype has been greatly improved, 
ai-e so great, that, Avith the incidental notice that we owe the 
application of bromine to Mr. Goddai-d, the consideration of 
them are postponed to the Tliird Part, as more entii'ely belong- 
ing to the manipulatory details. 



The researclies of Sir "John Herschel have been principally 
directed to the investigation of the physical laws which regulate 
the chemical changes we have been considering. His analyses 
of the prismatic spectrum have been most complete, and, as far 
as they have been earned out, go to prove the operation of forces 
other than those with which we are acquainted. 

At the same time, however, as this philosopher has been 
encaged in investigations of this high order, he has, from the 
midtitude of his experiments, been successfiil in producing 
several processes of great beauty. There are not any which are 
to be regarded as peculiarly sensitive — they are indeed for the 
most part rather slow — but the manipulation required is of the 
easiest character, and the residts are most ciuious and instructive. 

The philosophy which is for ever united with the scientific 
investigations of Sir John Herschel, is too valuable to be omitted 
from any description of the processes which he recommends ; 
the following quotations are therefore taken fr-om his communi- 
cation to the E-oyal Society, and Hnked together by my own 
remarks in such a manner as it is hoped will be most easily 
understood by the unscientific amateui*. 

Section I. — Cyanotype. 

The processes in which cyanogen is employed are so called : — 
Su- John Herschel makes the following remarks on the subject 
of his experiments with the cyanides : — 

" I shall conclude this part of my subject by remarking on the 
great niimber and variety of substances which, now that atten- 
tion is di-awn to the subject, appear to be i:)hotogra2jhically 
impressible. It is no longer an insidated and anomalous afiec- 
tion of certain salts of silver or gold, but one which, doubtless, 
in a greater or less degi'ee peiwades all natm-e, and connects 
itself intimately with the mechanism by which chemical combi- 
nation and decomposition is operated. The general instability 

SIR J. herschel's cyanottpe. 49 

of organic combinations might lead us to expect the occurrence 
of numerous and remarkable cases of this affection among bodies 
of that class, but among metallic and other elements inorganic- 
ally arranged, instances enough have ah-eady appeared, and more 
are daily presenting themselves, to justify its extension to all 
cases in which chemical elements may be supposed combined 
with a certain degree of laxity, and so to speak in a tottering 
equilibrium. There can be no doubt that the process, in a gi-eat 
majority, if not in all, cases which have been noticed among in- 
organic substances, is a deoxidising one, so far as the more re- 
frangible rays are concerned. It is obviously so in the cases of 
gold and silver. In that of the bichromate of potash it is most 
probable that an atom of oxygen is parted with, and so of many 
othei-s. A beautiful example of such deoxidising action on a 
non-argentine compoim.d has lately occiu'red to me in the exami- 
nation of that interesting salt, the feiTosesquicyanuret of potas- 
sium, described by Mr. Smee in the Fhilosophical Magazine, No. 
109, September, 1840, and which he has shown how to manu- 
factiu'e in abundance and piu-ity, by voltaic action on the com- 
mon, or yellow ferrocyanuret. In this process nascent oxygen 
is absorbed, hycb-ogen given off; and the characters of the 
resulting compound in respect of the oxides of iron, forming, 
as it does, Pi-ussian blue with protosalts of that metal, but pro- 
ducing no precipitate with its persalts, indicate an excess of 
electro-negative energy, a disposition to part with oxygen, or, 
which is the same thing, to absorb hych-ogen (in the presence of 
moistiu-e), and thereby to return to its pristine state under cir- 
cirmstances of moderate solicitation, such as the affinity of jjrotoxide 
of iron (for instance), for an additional dose of oxygen, (fcc. 

" Paper simply washed with a solution of this salt is highly 
sensitive to the action of light. Pi-ussian blue is deposited (the 
base being neces.sai'ily supplied by the destruction of one 
portion of the acid, and the acid by decomposition of another). 
After half an hour or an hoiu-'s exposure to sunshine, a veiy 
beautiful negative photogi-ajih is the result, to fix which, all that 
is necessary is to soak it in water in which a little sulphate of 
soda is dissolved, to ensure the fix;ity of the Pi-ussian blue de- 
posited. "While diy the impression is dove-coloiu- or lavender 
blue, which has a ciuious and striking effect on the greenish- 
yellow ground of the paper, produced by the saline solution. 
After washing, the gi-ound coloiu- disappears, and the photogi-aph 
becomes bright blue on a white groimd. If too long exposed, 
it gets 'over sunned,' and the tint has a brownish or yellowish 
tendency, which, however, is removed in fixing ; but no increase 


of intensity beyond a certain point is obtained by continuance 
of exposiu'e. 

" If paper be waslied with a solution of ammonio-citi-ate of 
iron, and dried, and tlien a wash passed over it of the yellow 
ferrocyanru'et of potassium, there is no immediate formation of 
true Prvissian blue, but the paper rapidly acquires a violet- 
piu'ple coloiu", which deepens after a few minutes, as it dries, to 
almost absolute blackness. In this state it is a positive photo- 
graphic paper of high sensibility, and gives pictures of great 
depth and sharpness ; but A\ith this peculiarity, that they darken 
again spontaneously on exposiu'e to the air in darkness, and are 
soon obliterated. The pajDer, however, remains susceptible to 
light, and capable of receiving other pictiu-es, which in their turn 
fade, without any possibility (so far as I can see) of arresting 
them; which is to be regretted, as they are very beautiful, and 
the paper of such easy preparation. If washed ^^dth ammonia 
or its carbonate, they are for a few moments entirely oblite- 
rated, hut presently reappear, toith reversed lights and shades. 
In this state they are fixed, and the ammonia, with all that it 
will dissolve, being removed by washing in water, their colour 
becomes a piu-e Prussian blue, which deepens much by keeping. 
If the solution be mixed, there results a very dark violet-coloured 
ink, which may be kejit uninjm-ed in an opaque bottle, and will 
readily fiu-nish, by a single wash, at a moment's notice, the 
positive paper in question, wliich is most sensitive when wet. 

" It seems at first sight natiu-al to refer these curious and 
complex changes to the instability of the cyanic compounds; 
and that this opinion is to a certain extent con-ect, is proved by 
the photographic impressions obtained on papers to which no 
ii'on has been added beyond what exists in the feiTocyanic salts 
themselves. Nevertheless, the following experiments abun- 
dantly prove that in several of the changes above described, the 
immediate action of the solar rays is not exerted on these 
salts, but on the iron contained in the ferruginous solution 
added to them, which it deoxidizes or othei-wise alters, thereby 
presenting it to the ferrocyanic salts in such a form as to 
precipitate the acids in combination with the peroxide, or 
protoxide of ii*on, as the case may be. To make this evident, 
all that is necessary is simply to leave out the ferrocyanate in 
the preparation of the paper, which thus becomes reduced to a 
simple washing over with the ammonio-citric solution. Paper 
so washed is of a bright yellow colour, and is apparently little, 
but in reality highly sensitive to photogi'aphic action. Exposed 
to strong sunshine, for some time indeed, its bright yellow tint 


is dulled into an oclu-ey liiie, or even to grey, but the change 
altogether amounts to a moderate per-centage of the total light 
reflected, and in short exposures is such as would easily escape 
notice. Nevertheless, if a slip of this paper be held for only 
four or five seconds in the suji (the effect of which is quite im- 
perceptible to the eye), and, when withdrawn into the shade, be 
washed over with the ferrosesquicyan'ate of potash, a conside- 
rable deposit of Pnissian blue takes place on the part sunned, 
and none whatever on the rest ; so tliat on washing the whole 
with water, a pretty strong blue impression is left, demonstrat- 
ing the reduction of ii'on in that portion of the paper to the 
state of protoxide. The effect in question is not, it should be 
observed, pecidiar to the ammonio-citrate of iron. The am- 
monio and potassia-tartrate fully possess, and the perchloride 
exactly neutralized, partakes of the same property : but the 
experiment is far more neatly made, and succeeds better, with 
the other salts." 

In further development of these most interesting processes 
Sir John Herschel says : — " The varieties of cyanotype pro- 
cesses seem to be innumerable, but that which I shall now 
describe deserves particidar notice, not only for its pre-eminent 
beauty while in progi-ess, but as illustrating the pecidiar power 
of the ammoniacal and other persalts of iron above-mentioned 
to receive a latent pictiu-e, susceptible of development by a 
gi'eat variety of stimuli. This process consists in simply passing 
over the ammonia-citrated paper on which such a latent 
pictm'e has been impressed, very sjxiringly and evenly, a wash of 
the solution of the common yellow ferrocyanate (prussiate) of 
potash. The latent picture, if not so faint as to be quite in- 
visible (and for this purpose it should not be so), is negative. 
As soon as the liquid is ajDpHed, which cannot be in too thin a 
film, the negative pictui'e vanishes, and by veiy slow degi'ees is 
replaced by a positive one of a violet-blue colour on a greenish- 
yellow gi-ound, which at a cei-tain moment possesses a high 
degi-ee of sharpness, and singular beauty and delicacy of tint. 
If at this instant it be thrown into water, it passes immediately 
to Prussian blue, losing at the same time, however, much of its 
sharpness, and sometimes indeed becoming quite blotty and 
confused. But if this be delayed, the picture, after attaining a 
certain maximum of distinctness, grows rapidly confused, es- 
pecially if the quantity of liquid applied be more than the paper 
can easily and completely absorb, or if the brush in applying it 
be allowed to rest on, or to be passed twice over any part. The 
effect then becomes that of a coarse and ill-printed woodcut, all 


the strong shades being nm together, and a total absence pre- 
vailing of half lights. 

" To prevent tliis confusion, gum-arabic may be added to the 
pnissiated solution, by wliich it is hindered from spreading un- 
manageablj -witliin the pores of the paper, and the precipitated 
Prussian blue allo-«-ed time to agglomerate and fix itself on the 
fibres. By the use of this ingi-edient also, a much thinner and 
more equable film may be spread over the siu'face ; and lohen 
perfectlij dry, if not sufficiently developed, the application may be 
repeated. By operating thus I have occasionally (though rarely) 
succeeded in producing pictures of great beauty and richness of 
efiect, which they retain (if not thrown into water) between the 
leaves of a portfolio, and have even a certain degi-ee of fixity — 
fading in a strong light, and recovering their tone in the dark. 
The manipiilations of tliis process are, however, delicate, and 
complete success is comparatively rare. 

" If sidphocyanate of potash be added to the ammonio-citrate 
or ammonio-tartrate of iron, the pecidiar red colour which that 
test induces on persalts of the metal Ls not produced, but it 
appears at once on adding a drop or two of dilute sulphiu'ic or 
nitric acid. This cii'cumstance, joined to the perfect neutrality 
of these salts, and theii' power, in such neuti-al solution, of 
endiu'ing, undecomposed, a boiling heat, contraiy to the usual 
habitudes of the peroxide of iron, together with theii* singvdar 
ti-ansformation by the action of light to proto-salts, in apparent 
opposition to a very strong affijiity, has, I confess, inclined me 
to speculate on the possibility of their ferruginous base existing 
in them, not in the ordinary foi'm of peroxide, but in one isome- 
ric with it. The non-formation of Pnissian blue, when their 
solutions are mixed -^dth prussiate of potash, and the formation 
in its place of a deep violet-coloiu'ed liquid of singulai* instability 
under the action of light, seems to favoiu' this idea. Nor is it 
altogether impossible that the peculiar "prepared" state super- 
ficially assumed by iron under the influence of nitric acid, first 
noticed by Keii', and since made the subject of exjieriment by 
M. Seohnbeia and myself, may depend on a change supei-ficially 
operated on the iron itself into a new metallic body isomeric 
with iron, unoxidable by nitric acid, and wliich may be consi- 
dered as the radical of that peroxide which exists in the salts in 
question, and possibly also of an isomeric protoxide. A combi- 
nation of the common protoxide with the isomeric peroxide, 
rather than with the same metal in a simply higher stage of 
oxidation, would afibrd a not unplausible notion of the chemical 
natm-e of that peculiar intermediate oxide to which the name of 

SLR s. herschel's cyanotype. 53- 

'Ferroso-fen'ic' has been given by Berzelius. If (to render my 
meaning more clear) we for a moment consent to designate such 
an isomeric form of ii'on by the name sideriuni, the oxide in 
question might be regarded as a sideriate of iron. Both phos- 
phoras and arsenic (boches remarkable for sesqui-combinations) 
admit isomeric forms in theu* oxides and acids. But to retiu-n 
from this digression. 

" If to a mixture of ammonio-citrate of u'on and sulphocyanate 
of potash, a small dose of nitric acid be added, the resvJting red 
liquid, spread on paper, spontaneously whitens in the dark. If 
more acid be added till the point is attained when the discolora- 
tion begins to relax, and the paper when dry retains a conside- 
I'able degree of coloiu-, it is powerfully affected by Hght, and 
receives a positive picture with great rapidity, which appears at 
the back of the paper with even more distinctness than on its 
face. The impression, however, is pallid, fades on keeping, nor 
am I acquainted at present with any mode of fixing it. 

"If paper be washed with a mixtm-e of the solutions of 
ammonio-citrate of ii'on and ferrosesquicyanate of potash, so as 
to contain the two salts in about equal proportions, and being 
then impressed with a picture, be tlu-own into water and di'ied, 
a negative blue image "will be produced. This picture I have 
found to be susceptible of a very cui'ious transformation, pre- 
ceded by total obliteration. To effect tliis it must be washed 
with solution of proto-nitrate of mercury, which in a little time 
entirely dischai'ges it. The nitrate being thoroughly washed 
out and the picture di'ied, a smooth iron is to be passed over it, 
somewhat hotter than is used for ii'oning linen, but not 
sufficiently so to scorch or injure the paper. The obhterated 
pictui-e immediately reappears, not blue, but brown. If kept for 
some weeks in this state between the leaves of a poi-tfoHo, in 
complete dai-kness, it fades, and at length almost entu-ely dis- 
appears. But what is very singular, a fi-esh application of the 
heat revives and restores it to its fiill intensity. 

" This curious transformation is instiiietive in another way. 
It is not operated by light, at least not by light alone. A certain 
temperature must be attained, and that temperatiu'e suffices in 
total darkness. Nevertheless, I find that on exposing to a very 
concentrated spectnim (collected by a lens of short focus) a slip 
of paper diily prepared as above (that is to say, by washing with 
the mixed solutions, exposiu-e to sunshine, washing, and dis- 
charging the uniform blue colour so induced as in the last 
article), its whiteness is changed to broA\Ti over the whole region 
of the red and orange rays, hut not beyond the luminous sijec- 
trum. Three conclusions seem unavoidable : — 1st, that it is the 


heat of these rays,, not theii' light, which operates the change ; 
2ndly, that this heat possesses a peculiar chemical quality which 
is not possessed by the purely calorific rays outside of the 
visible spectrum, though far more intense ; and, 3rdly, that the 
heat radiated from obscurely hot ii-on abounds especially in rays 
analogous to those of the region of the spectiixm above 

Sir John Hei-schel then proceeds to show that whatever be 
the state of the ii'on in the double salts in question, its reduction 
by blue light to the state of protoxide is indicated by many 
other reagents. Thus, for example, if a slip of paper prepared 
with the ammonio-citrate of iron be exposed partially to sun- 
shine, and then washed with the bichi-omate of potash, the 
bichromate is deoxidised, and precipitated upon the svmned 
portion, just as it would be if directly exposed to the siin's 

I have proved this fact with a great number of prepai-ations 
of cobalt, nickel, bismuth, platinum, and other salts which have 
been thought hitherto to be insensible to solar agency ; but if 
they are partially sunned, and then washed with nitrate of silver, 
and put aside in the dark, the metallic silver is slowly reduced 
upon the sumied portion. In many instances days were required 
to produce the visible picture ; and in one case, paper, being 
washed -svith neutral chloride of platinum, was sunned, and then 
washed ia the dark with nitrate of silver: it was some weeks 
before the image made its appearance, but it was eventually per- 
fectly developed. This specimen has been kept for several years, 
and continues constantly to improve in clearness and definition. 

Section II. — Chrysottpe. 

A process of an analogous character to that which has just 
been described, and in which the chloride of gold is an agent, 
must be next described : this was discovered at the same time 
as the cyanotype, and has been termed the chrysotyi^e. 

" In order to ascertain whether any poi-tion of the iron in the 
double ammoniacal salt employed had really imdergone deoxida- 
tion, and become reduced to the state of protoxide, as si;pposed, 
I had recourse to a solution of gold exactly neutralised by 
carbonate of soda. The proto-salts of iron, as is well known to 
chemists, precipitate gold in the metallic state. The effect 
proved exceedingly striking, issuing in a process nowise in- 
ferior in the almost magical beauty of its effect to the calotype 
process of Mr. Talbot, which in some respects it nearly resembles ; 

SIR J. herschel's chrysotype. 55 

with this advantage, as a matter of expei'imeiital exhibition, that 
the disclosiu-e of the dormant image does not requii'e to he per- 
formed in the dark, being not interfered with by moderate day- 
light. As the experiment will probably be repeated by others, 
I shall here describe it ab initio. Paper is to be washed 
with a moderately concentrated solution of ammonio-citrate of 
iron, and dried. The strength of the solution should be such as 
to dry into a good yellow coloiir, not at all brown. In this state 
it is ready to receive a photographic image, which may be im- 
pressed on it either from nature in the camera obscura, or from 
an engi"aving on a frame in sunshine. The image so impressed, 
however, is very faint, and sometimes hardly perceptible. The 
moment it is removed from the frame or camera, it must be 
washed over with a neutral solution of sold of such strenscth as 
to have about the colour of sherry wine. Instantly the picture 
appeal's, not, indeed, at once of its fiill intensity, but dai-kening 
with great rapidity up to a certaia point, depending on the 
strength of the solutions used, »tc. At this point nothing can 
siu-pass the sharpness and perfection of detail of the resulting 
photograph. To arrest this process and to fix the picture (so 
far at least as the further agency of light is concerned), it is to 
be thi-own into water very slightly acidulated with sulphiu-ic 
acid, and well soaked, dried, washed ^^■ith hydrobromate of 
potash, rinsed, and dried again. 

" Such is the outline of a process to which I propose applying 
the name of Chrysotype, in order to recall, by similarity of struc- 
ture and termination, the Calotype process of Mr Talbot, to 
which, in its general efiect, it affords so close a parallel. Being 
veiy recent, I have not yet (Jvme 10, 1842) obtained a complete 
command over all its details, but the termination of the session 
of the Society being close at hand, I have not thought it 
advisable to suppress its mention. In point of direct sensibility, 
the chiysotype paper is certainly inferior to the calotj^e ; but it 
is one of the most remarkable peculiarities of gold as a photo- 
graphic ingredient, that extremely feeble impressions once made 
by light go on afterwards darkening spontanemisly and very slowly, 
Ojpparerdly vnthout limit, so long as the least vestige of unreduced 
chloride cf gold remains in the paper. To illustrate tliis curious 
and (so far as applications go), highly impoi*tant property, I shall 
mention incidentally the results of some experiments made, 
during the late fine weather, on the habitudes of gold in presence 
of oxalic acid. It is well known to chemists that this acid, 
heated with solutions of gold, precipitates the metal in its 
metallic state ; it is iipon this j^roperty that BerzeUus has 
founded his determination of the atomic weight of gold. Light, 


as well as heat, also operates this precipitation ; but to rendei' 
it effectual, several conditions are necessary : — 1st, the solution 
of gold must be neutral, or at most very slightly acid ; 2nd, the 
oxalic acid must be added in the form of a neutral oxalate ; 
and 3rdly, it must be present in a certain considerable quantity, 
which quantity must be greater the greater the amomit of free 
acid present in the chloride. Under these conditions, the gold 
is precipitated by light as a black powder if the liquid be in any 
bulk, and if merely washed over paper a stain is produced, which, 
however feeble at first, under a cei-tain dosage of the chloride, 
oxalate, and free acid, goes on increasing from day to day and 
fi'om week to week, when laid by in the dark, and especially in 
a damp atmosphere, till it acqiiii'es almost the blackness of ink ; 
tlie unsunned portion of the paper remaining unaffected, or so 
slightly as to render it almost certain that what little action of 
the kind exists is due to the effect of casual dispersed light 
incident in the preparation of the paper. I have before me a 
specimen of paper so treated in which the effect of thirty 
seconds' exposiu-e to sunshine was quite invisible at first, and 
which is now of so intense a purple as may well be called black, 
while the imsunned portion has acquired comparatively but a 
very slight brown. And (which is not a little remarkable, and 
indicates that in the time of exposui-e mentioned the maximum 
of effect was attained) other portions of the same paper exposed 
in graduated progression for longer times, viz. 1 min., 2 min., 
and 3 min., are not in the least perceptible degree darker than 
the portion on which the light had acted during thirty seconds 

" If paper prepared as above recommended for the crysotype, 
either "with the ammonio-citrate or ammonio-tartrate of iron, and 
impressed, as in that process, with a latent picture, be washed 
with nitrate of silver instead of a solution of gold, a very sharp 
and beautifid pictui'e is developed, of great intensity. Its dis- 
closure is not instantaneous ; a few moments elapse without 
apparent effect ; the dark shades are then first touched in, and 
by degrees the details appear, but much more slowly than in the 
case of gold. In two or thi'ee minutes, however, the maximiun 
of distinctness will not fail to be attained. The picture may be 
fixed by the hyposulphite of soda, which alone, I believe, can be 
fully depended on for fixing argentine photographs. 

" The best process for fixing any of the photographs prepared 
with gold is as follows : — As soon as the pictm-e is satisfactorily 
brought out by the aiu'iferous liquid, it is to be rinsed in spring 
water, which must be three times renewed, letting it I'emain in 
the third water five or ten minutes. It is then to be blotted off 


and dried, after -which it is to be washed on both sides with a 
somewhat weak solution of hvdriodate of potash (iodide of fotas- 
sium). If there be any fi-ee chloride of gold present in the pores of 
paper, it will be discoloured, the lights passing to a ruddy brown ; 
but they speedily whiten again spontaneously, or at all events on 
throwing it (after lying a minute or ttvo,) into fresh water, in 
which, being again rinsed and di'ied, it is now perfectly fixed." 

Section III. — Photographic Properties of Mercury. 

" As an agent in the dagueiTeotj'pe process, it is not, strictly 
speaking, photographically affected. It opei-ates there only in 
\"ii-tue of its readiness to amalgamate with silver pr-operly pre- 
pared to receive it. That it possesses direct photographic sus- 
ceptibility, however, in a veiy eminent degree, is proved by the 
following experiment. Let a paper be washed over with a weak 
solution of periodide of ii'on, and, when dry, with a solution of 
proto-niti-ate of mercury. A bright yellow paper is produced, 
which (if the right strength of the liquids be hit) is exceedingly 
sensitive while wet, darkening to a bro-wn coloiu- in a very few 
seconds in the sunshine. Withdra^^^l, the impression fades 
rapidly, and the paper in a few horns recovers its original colour. 
In operating this change of colour, the whole spectrum is effec- 
tive, "ss-ith the exception of the thei-mic rays beyond the red. 

" Proto-nitrate of merciuy simply washed over paper, is slowly 
and feebly blackened by exposui-e to sunshine. And if paper 
be impregnated with the ammonio-citrate of iron, already so 
often mentioned, partially sunned, and then washed with the 
proto-nitrate, a reduction of the latter salt, and consequently 
blackening of the paj^er, takes place very slowly in the dark over 
the sunned portion, to nearly the same amount as in the dii-ect 
action of the Hght on the simply nitrated paper. 

" But if the mercxuial salt be subjected to the action of light 
in contact vnih the ammonio-citrate or tartrate, the efiect is far 
more powerful. Considering, at present, only the citric double 
salt, a paper prepared by washing fii'st with that salt and then 
with the mercuiial proto-nitrate (diying between) is endowed 
with considerable sensibility, and dai'kens to a very deep broAvn, 
nay, to complete blackness, on a moderate exposure to good 
sun. Veiy sharp and intense photographs of a negative cha- 
racter may be thus taken. They are, however, difficult to Jix. 
The only method which I have foimd at all to succeed has been 
by washing them with bichromate of potash and soaking them 
for twenty-foui- hours in water, which dissolves out the chi'omate 


of mercury for the most part ; leaving, however, a yellow tint 
on the groimd, which resists obstinately. But though pretty 
effectually fixed in this way against light, they are not so against 
time, as they fade considerably on keeping. 

" When the proto-niti-ate of mercury is mixed, in solution, with 
either of the ammoniucal double salts, it forms a precipitate, which, 
worked up -with a brush to the consistence of cream, and spread 
upon paper, produces very fine pictures, the intensity of which it 
is almost impossible to go beyond. Most unfortunately, they 
cannot be preserved. Every attempt to fix them has resulted 
in the destruction of their beauty and force ; and even when 
kept from light, they fade with more or less rapidity, some 
disappearing almost entii^ely in three or foui- days, while others 
have resisted tolerably well for a fortnight, or even a month. 
It is to an over-dose of tartaric acid that their more rapid deterio- 
ration seems to be due, and of coui-se it is important to keep 
down the proportion of this ingredient as low as jiossible. But 
wthout it I have never succeeded in producing that peculiar 
velvety aspect on which the charm of these pictiu'es chiefly 
depends, nor anything like the same iutensity of colom* without 

Section IV. — Ferro-Tartbate of Silver. 

Extending his inquiries still fiu'ther into these very remarkable 
changes, the following process presented itself to Sir J. Herschel, 
which is hi many respects remarkable. 

If nitrate of silver, sj^ecific gra^-ity 1 -200, be added to ferro- 
tartaric acid, specific gravity 1'023, a precipitate falls, which is 
in great measure redissolved by a gentle heat, leaving a black 
sediment, v/hich, being cleared by subsidence, a liquid of a pale 
yellow coloiu' is obtained, in which a fui'ther addition of the 
nitrate causes no tvu-bidness. When the total quantity of the 
nitrated solution amounts to about half the bulk of the ferro- 
tartaric acid, it is enough. The liquid so prepared does not 
alter by keeping in the dark. 

Spread on paper, and exposed wet to the sunshine (partly 
shaded) for a few seconds, no impression seems to have been 
made ; but by degrees (although withdi'awn from the action of 
the light) it developes itself spontaneously, and at length be- 
comes very intense. But if the paper be thoroughly di-ied in 
the dark (in which state it is of a very pale gi'eenish-yellow 
colour), it possesses the singidar property of recei\'ing a dormant 
or invisible picture j to produce which (if it be, for instance, an 


engraving that is to be copied), from thirty seconds' to a minute's 
exposTire in the stmshine is requisite. It should not be continued 
too long, as not only is the ultimate effect less stiiking, but a 
picture begins to be ^-isibly produced, which dai-kens spont- 
neously after it is 'withch-a-mi. But if the exposiu-e be discon- 
tinued before this effect comes on, an invisible impression is the 
result, to develope which aU that is necessary is to breathe upon 
it, when it immediately appears, and very speedily acquires an 
extraordinary intensity and shai-pness, as if by magic. Instead 
of the breath, it may be subjected to the regulated action of 
aqueous vapour by laying it in a blotting-paper book, of which 
some of the outer leaves on both sides have been damp, or by 
holding it over warm water. 

Many preparations, both of silver and gold, possess a similar 
property, in an inferior degi-ee ; but none that I have yet met 
with, to anything like the extent of that above described. 

These pictiu-es do not admit of being pennanently fixed ; they 
are so against the action of light, but not against the operations 
of time. They slowly fade out even in the dark ; and in some 
examples which I have prepared, the remarkable phenomenon 
of a restoration after fading, but vriih reversed Kghts and shades, 
has taken place. 

Section Y. — The Amphitype. 

The following very remarkable process was communicated by 
Sir John Herschel, at the meeting of the British Association at 
York. The process cannot be regarded as perfect, but from its 
beauty when success is obtained, and the cui-ious nature of aU 
its phenomena, it is deemed important to include it, ia the hope 
of inducing some investigator to take it up. 

Su- John Herschel says, alluding to the processes just de- 
scribed, '•' I had hoped to have perfected this process so far as to 
have reduced it to a definite statement of manipvdations which 
would insure success. But, capricious as photogi-aphic processes 
notoriously are, this has proved so, even beyond the ordinary 
measure of such caprice. * * * Paper proper for producing 
an amphitype pictiu-e may be prepared either with the ferro- 
tartrate or the ferro-citrate of the protoxide or the peroxide of 
mercun^, or of the protoxide of lead, by u.sing creams of these 
salts, or by successive applications of the nitrates of the respec- 
tive oxides, singly or in mixtiu-e, to the paper, alternating with 
solutions of the ammonio-tarti-ate or ammonio-eitrate of iron, 
the latter solution being last applied, and in more or less ex- 


cess. * ■■* " Paper so prepared aud diied takes a negative 
pictxire, in time varying from half an hour to five or six hours, 
according to the intensity of the light; ?nd the impression pro- 
duced varies in apparent force from a faint and hardly percep- 
tible pictm-e to one of the highest conceivable ftilness and rich- 
ness both of tint and detail, the colour in this case being a 
superb velvety browna. This extreme richness of effect is not 
produced except lead be present either in the ingredients used, 
or in the paper itself. It is not, as I origiually supposed, due to 
the presence of free tartaric acid. The pictures in. this state 
are not pennanent. They fade in the dark, though with very 
different degrees of rapidity, some (especially if free tartaric or 
citric acid be present) in a few days; w^hile others remain for 
weeks unimpafred, and require whole years for their total ob- 
literation. But, though entii'ely faded out in appearance, the 
pictui-e is only rendered dormant, and may be restored, chang- 
ing its character fr-om negative to positive, and its colour' from 
bro^-n to black (in the shadows) by the folloA\-ing process : — 
A bath being prepared by ponring a small quantity of solution 
of per-nitrate of merciuy into a large quantity of water, and 
letting the sub-nitrated precipitate subside, the pictui-e must be 
immersed in it (carefidly and repeatedly cleai'ing off the air- 
bubbles) and allowed to remain till the picture (if anywhere 
"\4sible) is entii"ely destroyed, or if faded, till it is judged suffi- 
cient from pre\"ious experience; a term which is often marked 
by the appearance of a feeble jDositive pictiu-e of a bright yellow 
hue on the pale yellow gi'ouud of the paper. A long time 
(several weeks) is often requii-ed for this, but heat accelerates 
the action, and it is often complete in a few houi's. In this 
state the pictm*e is to be veiy thoroughly rinsed and soaked in 
pure warm water, and then cfried. It is then to be well ii-oned 
with a smooth iron, heated so as barely not to injm-e the paper, 
placing it, for better security against scorching, between smooth 
clean papers. If, then, the process have been successful, a j^er- 
fectly black positive pictui-e is at once developed. At first it 
most commonly happens that the whole picture is sooty or 
dingy to such a degree that it is condemned as spoiled, but on 
keeping it between the leaves of a book, especially in a moist 
atmosphere, by extremely slow degrees this dinginess disap- 
pears, and the picture disengages itself A\'ith continually in- 
creasing sharpness and clearness, and acquii-es the exact effect 
of a copperplate engraving on a paper more or less tinted with 
pale yellow. 

" I ought to observe, that the best and most unifonn speci- 
mens which I have procured have been on paper previously 


washed -wdth ceHain preparations of vu'ic acid, which is a veiy 
remarkable and powerful photographic element. The intensity 
of the original negative picture is no criterion of what may be 
expected in the positive. It is from the production, by one and 
the same action of the light, of either a positive or a negative 
picture, according to the subsequent manipulations, that I have 
designated the process thus generally sketched out, by the tenn 
" Ani2Jhitype f a name suggested by Mr. Talbot, to whom 1 
communicated this singiilar result ; and to this process or class 
of processes (which I cannot doubt when piu'sued will lead to 
some veiy beautiful results) I propose to restrict the name in 
question, though it applies even more ajipropriately to the fol- 
lowing exceedingly curious and remarkable one in which silver 
is concerned. At the last meeting I annoimced a mode of pro- 
ducing, by means of a solution of silver in conjunction with 
ferro-tartaric acid, a dormant picture brought out into a forci- 
ble negative impression by the breath, or moist aii-. The solu- 
tion then descx'ibed, and which had at that time been prepared 
some weeks, I may here accidentally remark, has retained its 
limpidity and photogTaphic properties quite unimpaii-ed dui'ing 
the whole year since elapsed, and is now as sensitive as ever — a 
property of no small value. Now, when a picture (for example, 
an impression from an engTaving) is taken on paper washed 
with this solution, it shows no sign of a picture on its back, 
whether that on its face be developed or not ; but if, while the 
actinic influence is still fresh iipon the face {i.e. as soon as it is 
removed from the light), the hack be exjDosed for a very few 
seconds to sunshine, and then removed to a gloomy place, a 
positive pictiu'e, the exact complement of the ner/ative one on the 
other side, thoiigh wanting of course in sharpness if the paper be 
thick, sloioly and gradually makes its appearance there, and in 
half an hour requires considerable intensity. I oiight to men- 
tion that the ferro-tartaric acid in question is prepared by pre- 
cipitating the feiTO-tartrate of ammonia by acetate of lead, and 
decomposing the precipitate by dilute stdphiu'ic acid." 

Section YI. — The Colouring Matter of Flowers. 

The residts obtained by Sir John Herschel on the colouring 
juices of flowers are too remaikable to be omitted in a treatise 
in which it is desirable that every point should be registered up 
to the date of publication, which connects itself with the pheno- 
mena of chemical change applied to photography. 

" In operating on the colouis of flowers, I have usually pro- 
ceeded as follows: — The petals of the fresh flowers, or rather 


STich parts of them as possessed a uniform tint, were cruslied 
to a pulp in a marble moii-ar, either alone, or "with addition of 
alcohol, and the juice expressed by squeezing the pulj) in a clean 
linen or cotton cloth. It was then spread on paper with a flat 
briLsh, and ckied in the air without artificial heat, or at most 
with the gentle warmth which rises in the ascending cuiTent of 
air ft'om an Amott stove. If alcohol be not added, the applica- 
tion on paper must be perfoi'med immediately, since exposure 
to the au- of the juices of most flowers (in some cases even but 
for a few minutes) iiTecoverably changes or destroys then* co- 
lour. If alcohol be present, this change does not usually take 
place, or is much retarded; for which reason, as well as on 
account of certain facilities afibrded by its admixture in pro- 
curing an even tint (to be presently stated), this addition was 
commonly, but not always, made. 

"Most flowers give out their colouring matter readily enough, 
either to alcohol or water. Some, however, as the Escholzias 
and Calceolarias, refuse to do so, and requii'e the adcUtion of 
alkalies, others of acids, &g. When alcohol is added, it should, 
however, be observed that the tint is often apparently much 
eufeebled, or even discharged altogether, and that the tinctm*e, 
when spread on paper, does not reappear of its blue intensity 
till after complete chying. The temporaiy destniction of the 
colour of the blue heartsease by alcohol Ls cmious, nor is it by 
any means a singular instance. In some, but in very few cases, 
it is destroyed, so as neither to reappear on chying, nor to be 
capable of revival by any means tried. And in all cases long 
keeping deteriorates the coloxirs and alters the qualities of the 
alcoholic tinctures themselves ; so that they should always be 
used as fresh as possible. 

" If papers tinged with vegetable colours are intended to be 
presei-ved, they must be kept perfectly dry and in darkness. 
A close tin vessel, the air of which is dried by quicklime (care- 
fiiUy enclosed in double paper bags, well pasted at the edges to 
prevent the dust escaping), is used for this pm^jose. Moisture 
(as already mentioned, especially assisted by heat) destroys them 
for the most pai-t rajjidly, though some (as the coloiu- of the 
Senecio sjjiendens) resist obstinately. Then- destructibihty by 
this agency, however, seems to bear no distinct relation to their 
photographic properties. 

" This is also the place to observe that the coloui' of a flower is 
by no means always, or usually, that which its expressed juice 
impai'ts to white paper. In many cases the tints so imparted 
have no resemblance to the original hue. Thus, to give only a 
few instances, the red damask rose of that intense variety of 


coloiir commonly called by florists the black rose, gives a dark 
slate blue, as do also the clove cai'uation and the black holly- 
hock : a fine dark bro^Ti variety of spai'axis give a dull olive 
gi-een ; and a beautiful rose-coloiu'ed tulip, a dii-ty bluish green ; 
but perhaps the most striking case of this kind is that of a com- 
mon sort of red poppy {Papaver Kheuni), whose expressed juice 
imparts to paper a rich and most beautiful Ijlue colour, whose 
elegant properties as a photographic material ^vtH be further 
alluded to hereafter. * 

" This change of coloiu' is probably owing to different causes 
in difierent flowers. In some it undoubtedly ai'ises from the 
escape of carbonic acid, but this, as a general cause for the change 
from red to blue, has, I am aware, been controverted. In some 
(as is the case "wdth the yellow ranunculi) it seems to arise from 
a chemical alteration depending on absorption of oxygen ; and in 
others, especially where the expresssd juice coagulates on stand- 
ing, to a loss of vitality or disorganization of the molecules. The 
fresh petal of a single flower, merely ciiished by rubbing on diy 
paper, and instantly dried, leaves a stain much more nearly ap- 
proximating to the original hue. This, for examjjle, is the only 
way in which the fine blue colovu- of the common field veronica 
can be imparted to paper. Its expressed juice, however quickly 
prepared when laid on with a bnish, afibrds only a dii-ty neutral 
grey, and so of many others. But in this way no even tint can 
be had, which is a fii-st requisite to the experiments now in ques- 
tion, as well as to their application to photogi-aphy. 

" To seciu'e this desirable evenness of tint, the following mani- 
pulation ^"ill generally be found successful ; — The pajjer should 
be moistened at the back by sponging and blotting off. It should 
then be pinned on a boai-d, the moist side do-^mwards, so that 
two of its edges (suppose the right-hand and lower ones) shall 
project a little beyond those of the board. The board being 
then inclined twenty or thii-ty degi-ees to the horizon, the alco- 
holic tinctm-e (mixed ^vith a very little water, if the petals them- 
selves be not very juicy) is to be applied "v\-ith a brush in strokes 
fi'om left to I'ight, taking care not to go over the edges which 
rest on the boai'd, but to pass cleai-ly over those which project, 
and observing also to carry the tint from below upwards by 
quick sweeping strokes, leaving no diy spaces between them, 
but keeping up a continuity of wet sm-face. When all is wet, 
cross them by another set of strokes from above downwards, so 
managing the brush as to leave no floating liquid on the paper, 

* A semi-cultivated variety was used, having dark purple spots at the bases 
of the petals. The common red poppy of the chalk {Fajjavier hyhridum) gives 
a purple colour much less sensitive aud beautiful. 


It must then be diied as quickly as jjossible over a stove, or in 
a cui-rent of "warm aii* ; avoiding, however, such heat as may 
injure the tint. The i:)resence of alcohol prevents the solution 
of the gummy 'principle, which, when present, gives a smeary 
surfiice ; but the evenness of tint given by this process results 
chiefly from that singular intestine movement which always 
takes place when alcohol is in the act of separation from water 
by evaporation ; a movement which dispei"ses knots and blots in 
the film of liquid "s\ great energy, and spreads them over the 
surrounding sui-face. 

" Corchorus Japonica. — The flowers of this common and hardy 
but highly ornamental plant are of a fine yellow, somewhat in- 
clining to orange, and this is also the coloui* the expressed juice 
imparts to paper. As the flower begins to fade the petals ivMten, — 
ajn indication of their photographic sensibility which is amply 
verified on exjjosiu-e of the stained paper to sunshine. I have 
hitherto met "sv-ith no vegetable coloiu- so sensitive. If the 
flowers be gathered in the height of then* season, paper so coloiu-ed 
(wliicli is of a very beautiful and even yellow) begins to discoloui" 
in ten or twelve minutes in cleai* sunshine, and in half an hour 
is completely whitened. The colour seems to resist the first 
impression of the light, as if by some remains of vitality, which 
being overcome, the tint gives way at once, and the discolora- 
tion, whem commenced, goes on rapidly. It does not even cease 
in the dark lohen once begun. Hence it happens that photographic 
impressions taken on such paper, which, when fresh, are very- 
sharp and beautiful, fade by keeping, visibly fr-om day to day, 
however carefully preserved fr-om light. They requii'e fr-om 
half an hoiu- to an hoiu- to complete, according to the sunshine. 
Hydi'iodate of potash cautiously applied retards considerably, but 
does not ultimately prevent, this spontaneous dischaige. 

'■'■Common Ten Weeks Stocks: 21 athiola annua. — Paper stained 
with the tincture of this flower is changed to a vivid scarlet by 
acids, and to green by alkalies ; if ammonia be used the red 
coloui- is restored as the ammonia evaporates, proving the absence 
of any acid quality in the coloiu-ing matter sufficiently energetic 
to coerce the elastic force of the alkaline gas. Sulphurous acid 
whitens it, as does the alkaline sulphites ; but this efiect is 
transient, and the red coloiu' is slowly restored by fr-ee exposure 
to ail-, especially \ni]i the aid of hght, whose influence in this case 
is the more remarkable, being exactly the reverse of its ordinary 
action on tliis coloui-ing principle, which it destroys irrecoverably, 
as above stated. The following experiments were made to trace 
and illustrate this ciu-ious change : — 

" Two photogi-aphic copies of engravings taken on paper tinted 


witli this colour were placed in a jar of sulpliiu-otis acid gas, by 
which they were completely whitened, and all traces of the pic- 
tures obliterated. They were then exposed to fi-ee air, the one 
in the dark, the other in sunshine. Both recovered, but the 
former much more slowly than the latter. The restoration of the 
picture exposed to the sun was completed in twenty-foiu' hours, 
that in the dai-k not till after a lapse of two or three days. 

" A slip of the stained paper was wetted with liquid sulphu- 
rous acid, and laid on blotting-jjaper similarly wetted. Being 
then crossed with a strip of black jiaper, it was laid between 
glass plates and (cTaporation of the acid being thns prevented) 
was exposed to fuU sunshine. After some time the red colour 
(in spite of the presence of the acid) was considerably restored 
in the portion exposed, wliile the whole of the portion covered 
by the black paper remained (of course) perfectly white. 

" Slips of paper, stained as above, were placed under a receiver, 
beside a small cajisule of liquid sulphurous acid. When com- 
pletely discoloui'ed, they were subjected (on various occasions, 
and after various lengths of exposure to the acid fiimes, from 
half an hoiu* to many days) to the action of the spectrum ; and 
it was found, as indeed I had expected, that the restoration of 
colour zvas ojierated hy rays coniplenientary to those lohich destroy 
it in the natural state of the paper ; the violet rays being chiefly 
active, the blue almost equally so, the green little, and the yel- 
low, orange, and most refrangible red, not at all. In one expe- 
riment a pretty-well defined red solar image was developed by 
the least refrangible red rays also, being precisely those for which, 
in the unprepai'ed paper the discolovuing action is abruptly cut 
off. But this spot I never succeeded in reproducing; and it 
ought also to be mentioned, that, according to differences in the 
preparation not ob^dous, the degree of sensibility, generally, of 
the bleached paper to the restorative action of light, differed 
gi'eatly ; in some cases a perceptible reddening being j^roduced 
in ten seconds, and a considerable streak in two miniites, while 
in others a veiy long time was requii-ed to produce any effect. 
The dormancy of this colouring principle, imder the influence of 
sulphiu-ous acid, is well shown by dropping a little weak sulphu- 
ric acid on the paper bleached by that gas, which immediately 
restores the red colour in all its vigour. In like mamier alka- 
nes restore the colour, converting it at the same time into green. 
" Pajxiver orientale. — The chemical habitudes of the sulphu- 
rous acid render it highly probable that its action in inducing a 
dormant state of the colorific principle, consists in a jiartial 
deoxidizement, unaccompanied, however, with disorganization of 
its molecules. And this view is coiToborated by the similar ac- 


tion of alcohol already spoken of; similar, tliat is, in kind, 
though less complete in degree. Most commonly, vegetable 
colours, weakened by the action of alcohol, are speedily restored 
on the total evaporation of the ingredient. But one remarkable 
instance of absolute dormancy induced by that agent has oc- 
curred to me in the case of Pajmver orientale, a flower of a vivid 
orange coloiu-, bordering on scarlet, the colom-ing matter of 
which is not extractable otherwise than by alcohol, and then 
only in a state so completely masked as to impart no more than 
a faint yellowish or pinkish hue to paper, which it retains when 
thoroughly dry, and apparently dm-ing any length of time, with- 
out perceptible increase of tint. If at any time, however, a 
di'op of weak acid be appHed to jDaper prepared with this tincture, 
a vivid scarlet coloiu- is inrmediately developed ; thus demon- 
stating the continued though latent existence of the coloming 
principle. On observing this, it occurred to me to inquire whe- 
ther, in its dormant state, that principle stUl retained its sus- 
ceptibility of being acted on by light, since the same powerful and 
delicate agent which had been shown, in so many cases as to con- 
stitute a general laAv, capable of disoi'ganizing and destroying 
vegetable coloiu-s actually developed, might easily be presumed 
competent to destroy the capacity for assuming colour, in such 
organic matter as might possess it, under the influence of their 
otherwise appropriate chemical stimuli. A strip of the paper 
was therefore exposed for an hour or two to the spectiixm, but 
without any sensible effect, the whole sm-face being equally red- 
dened by an acid. As tlus experiment sufficiently indicated the 
action of light, if any, to be very slow, I next placed a strip, 
partly covered, in a south-east window, where it remained from 
June 19 to August 19, receiving the few and scanty sunbeams 
which that interval of the deplorable summer of 1841 afforded. 
When removed, the part exposed could barely be distinguished 
from the part shaded, as a trifle yellower. But on applying 
acid, the exposed and shaded portions were at once distinguished 
by the assumption of a vivid red in the latter, and the former 
remaining u.nchaiiged. 

" A mezzotinto pictiu'e was now pressed on a glazed frame over 
another portion of the same paper, and abandoned on the upper 
shelf of a green-house to whatever sun might occm- from August 
19 to October 19. The interval proved one of almost uninter- 
rupted storm, rain, and darkness. On removal, no appearance 
whatever of any im^jressed pictm-e coidd be discerned, nor was 
it even possible to tell the top of the pictm-e from the bottom. It 
was then exposed in a glass jar to the fumes of miuriatic acid, 
when, after a few minutes, the development of the dormant pic- 


tiire commenced, and slowly proceeded, disclosing the details in 
a soft and pleasing style. Being then laid by in a drawer, with 
free access of aii*, the picture again faded, by very slow degi'ees, 
and on January 2, 1842, was foimd quite obliterated. Being 
then sxibjected to the acid vapoiu' the colour was reproduced. 

" Viola odorata. — Chemists are familiar with the colour of this 
flower as a test of acids and alkalies, for which, however, it seems 
by no means better adapted than many othei-s ; less so, indeed, 
than that of the Violar tricolor, the common puqjle ii'is, and 
many others which might be named. It offers, in fact, another 
and rather a striking instance of the simultaneous existence of 
two coloiuing ingredients in the same flower, comporting them- 
selves differently, not only in regard to light but to chemical 
agents. Extracted with, alcohol, the juice of the violet is of a 
rich blue coloiu-, which it impai-ts in high perfection to paj^er. 
Exposed to sunshine, a portion of this colour gives way pretty 
readily, but a residual blue, rather inclining to greenish, resists 
ob,stinately, and requires a very much longer exposure (for whole 
weeks, indeed) for its destruction, which is not even then com- 
plete. Photographic impressions, therefore, taken on this paper, 
though veiy pretty, are exceedingly tedious in their preperation, 
if we would have the lights sharply made out. 

" Sparaxis tricolor ?, var. — Stimulating Effects of Akcdies. — 
Among a gi-eat many hybrid varieties of this genus, lately for- 
warded to me from the Cape, occiu-red one of a very intense pur- 
plish-brown colour, nearly black. The alcoholic extract of this 
flower in its liquid state is rich crimson-bro-wni. Spread on paper, 
it imparted a dark olive-green colom-, which proved perfectly in- 
sensible to veiy prolonged action, either of sunshine or the 
spectrum. The addition of carbonate of soda changed the colour 
of this tincture to a good gi'een, slightly inclining to olive, and 
which imparted the same tint to paper. In this state, to my 
surprise, it manifested rather a high degree of photographic sen- 
sibility, and gave very pretty pictures with a day or two of ex- 
posiu-e to sunshine. When prepared with the fresh juice there 
is hardly any residual tint, but if the j^aper be kept, a gi-eat 
amoimt of indestiiictible yellow remains outstanding. The ac- 
tion is confined chiefly to the negative end of the spectiiim; all 
but the fii-st five or six parts beyond the yeUow show little more 
than a trace of action. A photogi-aph impressed on this paper 
is reddened by muriatic acid fumes. If then transferred to an 
atmosphere of ammonia, and when super-satiu"ated the excess of 
alkali allowed to exhale, it is fixed, and of a dark green colour. 
Both the tint and sharpness of the picture, however, sufler 
in this process. 


" Red Poppy : Papaver Rheum 1 — Among the vegetable coloiu-s 
totally destroyed by light, or wliicli leave no residual tint, at 
least when fresh prepared, perhaps the two most rich and 
beautiful are those of the red poppy and the double purple 
groundsel (Senecio sjdendensj. The former owes its red coloiu- 
in all probability to free cai'bonic acid, or some other (as the 
acetic), completely expelled by drying : for the colour its tincture 
imparts to paper, instead of red, is a fine blue very slightly 
verging on slate-blue. But it has by no means the ordinary 
chemical characters of blue vegetable colours. Cai-bonate of 
soda, for instance, does not in the least degree tiu'n the expressed 
juice gi-een ; and when washed with the mixtu,re, a paper results 
of a light slate-grey, hardly at all inclining to green. The blue 
tincture is considerably sensitive, and from the ricliness of its 
tone and the absence of residual tint, paper stained with it 
affords photographic impressions of great beauty and sharpness, 
some of which will be found among the collection submitted 
with this paper for inspection. 

"Senecio sjylendens. — This flower yields a rich piirple juice in 
great abimdance and of surprising intensity. Nothing can 
exceed the rich and velvety tint of paper tinted while it is fresh. 
It is, however, not very sensible to light, and many weeks are 
necessaiy to obtain a good photographic impression." 

In the progress of my own researches on this subject, I found 
that the green colouiing matter of the leaves of herbaceous 
plants, when spread upon paper, changed with tolerable rapidity 
when exjiosed to simshine. There are, however, some very 
curious points connected with the phenomena of these changes 
which demand a far more extensive investigation than they have 
yet received. 

I find that the juices taken from the leaves in the spring, 
change more rapidly than when expressed from the same plants 
in the autumn ; and the juices of those flowei"ing plants which 
have been cultivated under the artificial circumstances of 
a store-house, or conservatory, are more readily afiected than 
such as are grown in the open air. Many of the experiments 
just described fimiish very instructive examples of the opera- 
tions of the solar rays upon, organic bodies, from which we may 
deduce important truths connected with natural phenomena. 


miscella:nt:ous processes. 

Section I. — Mr. Ponton's Process. (Bichromate of 

Under the general term of the Chromatyije, I would propose to 
include all those processes which involve the use of any of the 
salts of chromium. It was originally introduced to distinguish 
a particular process which I discovei'ed, and published at the 
meeting of the British Association at Cork, in August 1843; 
biit it ajjj^ears very convenient to adopt the princijile intro- 
duced by Sir John Herschel, of grouping the phenomena of 
photogi'aphy imder special terms derived from the most prominent 
chemical jjrepai-ation employed. 

There are many preparations which are affected by Kght in a 
similar manner to the salts of silver. Several have been tried as 
photogi-ajjhic materials, but as yet without much success, with 
the exception of the bichromate of potash, which was &st an- 
nounced as a useful photographic agent by Mr. 'Mungo Ponton, 
in the Edinburgh New Philosophical Joiu-nal ; from which I 
quote Mr Ponton's own accoimt. 

" "When paper is immersed ia the bichromate of potash, it is 
powerfidly and rapidly acted on by the sun's rays. When an 
object is laid in the usual way on this paper, the portion exposed 
to the light speedily becomes tawny, passing more or less into 
a deep orange, accorcHng to the strength of the light. The por- 
tion covered by the object retains the original bright yellow tint 
which it had before exposure, and the object is thus represented 
yellow upon an orange ground, there being several gradations of 
shade, or tint, according to the greater or less degree of trans- 
parency in the different parts of the object. 

" In this state, of course, the drawing, though very beautiftil, 
is evanescent. To fix it, all that is required is careftil immersion 
in water, when it will be found that those portions of the salt 
which have not been acted on by the light are readily dissolved 
out, wliile those which have been exposed to the light are com- 
pletely fixed on the paper. By the second process the object is 
obtained white upon an orange ground, and quite permanent. If 
exposed for many hoiu-s together to strong simshine, the colour 
of the ground is apt to lose in depth, but not more so than most 
other coloming matters. This action of light on the bichromate 


of potasli differs from that upon the salts of silver. Those of the 
latter which are blackened by light are of themselves insoluble 
in water, and it is difficult to impregnate paper with them in a 
uniform manner. The blackening seems to be caused by the for- 
mation of oxide of silver. 

" In the case of the bichromate of potash, again, that salt is 
exceedingly soluble, and paper can be easily satui-ated with it. 
The agency of light not only changes its coloiu-, but deprives it 
of solubility, thus rendering it fixed in the paper. This action 
appears to consist in the disengagement of fi-ee chromic acid, 
which is of a deep red coloui", and which seems to combiue with 
the paper. This is rendered more probable from the circum- 
stance that the neutral chi-omate exhibits no similar change. 
The best mode of preparing paper with bichromate of potash is 
to use a satiu'ated solution of that salt ; soak the pa^^er well in 
it, and then dry it rapidly at a bi-isk fii-e, excluding it from day- 
light. Paper thus prepared acquii'es a deep orange tint on ex- 
posiu-e to the sun. If the solution be less strong, or the chying 
less rapid, the colonr will not be so deep. A pleasing variety 
may be made by using sidphate of indigo along with the biclii'o- 
mate of potash, the coloiu* of the object and of the paper being 
then different shades of gi'een. In this way, also, the object 
may be represented of a darker shade than the ground." 

Paper prepared with the bichromate of potash, though as 
sensitive as some of the papers prepared with the salts of silver, 
is mvich inferior to most of them, and is not sufficiently sensitive 
for the camera obscm-a. This paper, however, answers quite 
well for taking drawings from dried plants, or for copying prints. 
Its great recommendation is its cheapness, and the facility with 
which it can be prepared. The price of the bichromate of potash 
is about two shillings per pound, whilst the nitrate of silver is 
five shillings the oujice. 

As the deep orange ground of these pictures prevents the per- 
meation of the chemical rays of light, it is very easy to procure 
any number of facsimiles of an engraving, by transfer from the 
first negative photograph. The correct copies have a beautiful 
sharpness; and, if carefidly managed, but Kttle of the minute 
detail of the original engraving is lost. 

A photogi-aphic paper prepared with the bichromate of 
potash of another kind is described by M. E. Becquerel. He 
states, — It is sufficient to steep a paper prejoared in Mr. Ponton's 
manner, and upon which there exists a faint copy of a drawing, 
in a solution of iodine in alcohol, to wash this paper in alcohol, 
and then diy it : then the parts which were white become blue, 
and those which were yellow remain more or less clear. 

ME. ponton's process. 71 

M. E. Becquerel lias pursued liis investigation!? into tlie action 
of the ckromic acid on organic compounds, and lias slio^vn that 
the mode of sizing the papers influences their coloration by 
light, and that with unsized paper coloration is effected only 
after a long time. Perceiving that the principal reaction re- 
svdted from the chromic acid contained in the bichromate of 
potash, on the starch in the size of the paper, it occniTed to ]M. 
E. Becquerel, that, as starch has the property of forming ^\-ith 
iodine a combination of a very fine blue colour, it should pro- 
duce deep shades of that tint, whilst the lights still remained an 

His method of proceeding is to spread a size of starch very 
uniformly over the surface of the paper. It is then steeped in 
a weak alcoholic solution of iodine, and aftenvai'ds washed in a 
great quantity of water. By this immersion it should take a 
very fine blue tint. If this is uniform, the paper is considered 
fit for the experiment ; in the contrary case it is sized again. 
It is then steeped in a concentrated solution of bichromate of 
potash, and pressed between folds of blotting-paper, and di-ied 
near the fire. To be effective, it should be very dry. 

It is now fit for use. When the copy is effected, which re- 
quires in sunshine about five minutes, the photogi-aph is washed 
and ch'ied. A\Tien diy, it is steeped in a weak alcoholic solution 
of iodine, and afterwards, when it has remained in it some time, 
it is washed in water, and carefully dried ^vith blotting-paper, 
but not at the fii*e, for at a little below 100® Fahr. the combi- 
nation of iodine and starch discolours. 

If it be considered that the drawing is not sufficiently dis- 
tinct, this immersion may be repeated several times; for by 
this means may be obtained the intensity of tone that is de- 
sired, which intensity can be changed at will by employing a 
more concentrated solution of iodine. 

When the paper is damp, the shades are of a veiy fine blue, 
but when it is dry the colour becomes deep violet. If while 
the di'awing is still wet it be covered with a lawyer of gum. 
ai-abic, the colour of the drawing is greatly presei'ved, and more 
beautiful when it is diy. When a paper is thus prepared, it 
loses at first a little of its tone, but it afterwards presei-ves its 
violet tint. 

Section II. — The Chromatype. 

This process, devised by the author, is a pleasing one in its 
results : it is exceedingly simple in its manipulatory details, and 


produces very cliai'ming positive pictures by the fii-st appKca- 
tion. The chromatype is founded on the above process of 
Mr. Ponton's: — 

One di-achm of sulphate of copper is dissolved in an ounce of 
distilled water, to which is added half an oimce of a saturated 
solution of bichi'omate of potash ; this solution is applied to the 
sui'face of the paper, and, when diy, it is fit for use, and may be 
kept for any length of time without spoiling. When exposed 
to sunshine, the first change is to a didl brown, and if checked 
in this stage of the process we get a negative pictiu-e, but if the 
action of the light is contiuued, the browning gives way, and 
we have a positive yellow pictm-e on a white groiind. In either 
case, if the paper, when removed from the sunshine, is washed 
over with a solution of nitrate of silver, a very beautiful positive 
pictui^e results. In practice, it will be found advantageous to 
allow the bleaching action to go on to some extent; the pictiu-e 
i-esulting from this will be clearer and more defined than that 
which is procured when the action is checked at the brown 
stage. To fijc these pictures it is necessary to remove the 
nitrate of silver, which is done by washing in pure water : if the 
water contains any muriates the picture sufiers, and long soak- 
ing in such water obliterates it, or if a few grains of common 
salt are added to the water, the apparent destruction is very 
rapid. The pictui'e is, however, capable of restoration ; all that 
is necessaiy being to expose it to sunshiue for a quarter of an 
hour, when it revives; but instead of being of a red colour, it 
becomes lilac, the shades of coloiu- depending upon the quantity 
of salt used to decompose the chromate of silver which forms 
the shadow parts of the pictiu-e. 

Mr. Bingham remarks on this process, that if we substitute 
sulphate of nickel for the sulphate of copper, the paper is more 
sensitive, and the pictui-e is more clearly developed by nitrate 
of silver. 

The following modification of this process possesses some ad- 
vantages. If to a solution of the sulphate of copper we add a 
solution of the neutral chromate of potash, a very copious brown 
precipitate falls, which is a tiiie chi'omate of copper. If this 
precipitate, after beiug well washed, is added to water acididated 
with sulphuric acid, it is dissolved, and a dichromatic solution is 
formed, which, when spread upon paper, is of a pure yellow. A 
very short exposure of the jjapers washed with this solution is 
quite snfficient to discharge all the yellow from the paper, and 
give it perfect whiteness. If an engraving is to be copied we 
proceed in the usual manner ; and we may either bring out the 
picture by placing the paper in a solution of carbonate of soda 


or potash, by which all the shadows are represented by the 
chromate of copper, or by washing the paper with nitrate of 
silver. It may sometimes happen that, o-wdng to deficient light, 
the photograph is darkened all over when the silver is applied : 
this colour, by keeping, is gradually removed, and the pictvu-e 
comes out clear and sharp. 

If the chromate of copper is dissolved in ammonia, a beautiful 
gi-een solution results, and if applied to paper acts similarly to 
those just described. 

The chromatype pictures, under certain conditions, afibrd a 
beautiful example of the changes which take place, slowly, in 
the dark, li'om the combined operations of the materials em- 

If we take a chi'omatype picture after it has been developed 
by the agency of either nitrate of silver, or of mercuiy, and 
place it aside in the dark, it will be found, after a few weeks, 
to have dai'kened considerably both in the lights and shadows. 
This darkening slowly increases, until eventually the pictiu-e is 
obliterated beneath a film of metallic silver or mercvuy; but, 
while the pictui-e has been fading out on one side, it has been 
developing itself on the other, and a veiy pleasing image is seen 
on the back. After some considerable time the metal on the 
front gives way again, the paper slowly whitens, and eventually 
the image is presented on both sides of the paper of equal in- 
tensity, in a good neutral tint upon a grey gToimd. These 
results, it will be remembered, are of a very similar character 
to those already described as peculiar to the amphitype process 
of Sii' John Hei'schel. 

Section III. — The Ferrotype. 

This process, which is of remarkable sensibility, was discovered 
by the author, and published in the Athenceum, under the name 
of the Energiatype ; but from a desire to group all those pictiu-es 
under a general head into which ii'on salts enter as an element, 
the present name is preferred. The preparation of the paper 
is as follows:' — Good letter-paper (Whatman's is the best) is 
washed over with the following solution, viz. : Five gi-ains of 
succinic acid (it is important that succinic free from any oil of 
amber, or adventitious mattei-, should be obtained) are to be 
dissolved in one fluid omice of water, to which are added about 
five grains of common salt, and half a (frachm of mucilage of 
gum ai-abic. When tlry, the paper is cfrawn over the surface of 
a solution of sixty grains of nitrate of sOver in one ounce of dis- 


tilled "water. Allowed to dry in tlie dark, the paper is now fit 
for use, is of a pure white, retains its coloiu", and may be pre- 
sented for a considerable time in a portfolio, until wanted for 

The preparation of this paper is by no means difficult, but 
requires care and attention. The solutions must be apjilied very 
equally over the paper, which should be immediately hung upon 
a frame or clothes' horse to dry. Extreme care must be taken 
that the paper be not exposed to light, after the nitrate of silver 
solution has been applied, until required for use. Many of the 
disappointments experienced by the experimenters on the ener- 
giatype are occasioned by a neglect of this precaution ; as, 
although no apparent effect may have been produced by the ex- 
posure, the clearness of the subsequent picture will be seriously 
injured. The succinic acid must also be very piu-e. "We shall 
now briefly describe the method of applying this process to the 
different purposes for which it is best adapted, premising that 
the varying circumstances of time, place, and light, will render 
necessaiy such modifications of the following directions as the 
experience of the operator may suggest. As a general rule, an 
open situation, sunshine, and, if jjossible, the morning sun, 
should be preferred, as the image is sharper, and the coloiir 
produced more intense, and less affected by the subsequent 
fixing process. 

In the camera, for a building or statue, an exposm'e of half a 
minute in strong sunshine is usually sufficient ; for a portrait, 
taken imder oi'dinary conditions, two or three minutes are 

When the paper is taken from the camera, nothing is visible 
upon it ; but by attending to the following directions the latent 
pictui'e will quickly dev elope itself. Having mixed together 
about one ch-achm of a saturated solution oi protosulq^hate of iron 
and two or three drachms oi mucilage of gu7n arabic, poiir a small 
quantity into a flat dish. Pass the prepared side of the paper 
taken from the camera rapidly over this mixture, taking care to 
insure complete contact in every part. If the paper has been 
sufficiently impressed, the picture will almost immediately appear, 
and the further action of the iron must be stopped by the appli- 
cation of a soft sponge and plenty of clean water. Should the 
image not appear immediately, or be imperfect in its details, the 
iron solution may be allowed to remain upon it a short time ; 
but it mvist then be kept distiirbed, by rapidly but lightly brush- 
ing it up, otherwise numerous black specks will form and 
destroy the photograph. Great care should be taken that the 
iron solution does not touch the back of the picture, which it 


will inevitably stain, and, the picture being a negative one, be 
rendered useless as a copy. A slight degi'ee of heat will assist 
the development of the image where the time of exposure has 
been too short. 

The picture should be carefully washed to take off any super- 
ficial blackness, and may then be permanently fixed by being 
soaked in water to which a small quantity of ammonia, or, better 
still, hyposulphite of soda, has been added. The paper must 
again be well soaked in clean water, to clear it from the soluble 
salts, and may then be di'ied and pressed. 

Exact copies of prints, feathers, leaves, &c., may be taken on 
the succinated paper by exposing them to the light in the 
copying-frame, until the margin of the prepared paper, which 
should be left imcovered, begins to change colour very slightly. 
If the object to be copied is thick, the surface must be allowed 
to assume a darker tint, or the light "w-ill not have peneti-ated to 
the paper. 

Positive copies of the camera negatives are prociu'ed in the 
same manner as the copies of the prints, &c., just described. 
Instead, however, of using the iron solution, the paper must be 
exposed to the light, in the frame, a sufficient time to obtain 
perfect copies. The progress of the pictiu^e may be observed by 
tui'ning up the comer of the paper, and, if not sufficiently done, 
replacing it exactly in the same position. They should be fixed 
with hyposulphite, as before directed. 

At the meeting of the British Association at York in 1844, 1 
showed, by a series of photogi-aphs, that the protosuliTiliate of 
iron was most efiective in developing any photographic images, 
on whatever argentiferous preparation they may have been re- 
ceived. Eveiy subsequent result has shown that with proper 
care it is the most energetic agent for developing with which we 
are acquainted. The difficulty of obtaining, and of preserving, 
the salt free of any peroxide, or a basic salt which falls as a 
brownish-yellow powder, has been the principal cause why it has 
not been so generally employed as the gallic acid : this can be 
insiu'ed by adding a few drops of sulphuric acid and some iron 
filings to the solution of the protosulphate of iron. 

Section IV. — The Catalysotype. 

This process of Dr. Wood's is capable of producing pictures 
of superior excellence. Owing to the inconstancy of the iodine 
compounds, it is a little uncertain, but, care being taken to in- 
sure the same degree of strength in the solutions, a very imiform 


good result may be obtained. The process and its modifications 
are thus described by the inventor. 

''Let well-glazed paper (I prefer that called wove post) be 
steeped in water to which hych'ochloric acid has been added in 
the proportion of two drops to three ounces. When well wet, 
let it be washed over with a mixtiu-e of syrup of iodide of iron 
half a drachm, water two drachms and a half, tinctiu-e of iodine 
one drop. 

" When this has remained on the paper for a few minutes, so 
as to be imbibed, dry it lightly with bibulolus paper, and being 
removed to a dark room, let it be washed over evenly, by means 
of a camel-hair pencil, with a sokition of nitrate of silver, ten 
grains to the ounce of distilled water. The paper is now ready 
for the camera. The sooner it is used the better ; as when the 
ingredients are not rightly mixed it is liable to spoil by keeping. 
The time I generally allow the paper to be exposed in the 
camera varies from two to thirty seconds ; in clear weather, 
without sunshine, the medium is about fifteen seconds. With 
a bright light, the pictm^e obtained is of a rich brown colour ; 
with a faint light, or a bright light for a very short time continued, 
it is black. For portraits out of doors, in the shade on a clear 
day, the time for sittuag is from ten to fifteen seconds. 

" If the light is strong, and the view to be taken extensive, the 
operator should be cautious not to leave the paper exposed for 
a longer period than five or six seconds, as the picture will ap- 
pear confused from all parts being equally acted on. In all 
cases, the shorter the time in which the picture is taken the 

" When the paper is removed from the camera no pictm-e is 
visible. However, when left in the dark, without any other 
preparation being used, for a period which varies with the length 
of time it was exposed, and the strength of the light, a negatiAje 
picture becomes gradually developed, until it arrives at a state 
of perfection which is not attained, I think, by photography 
produced by any other process.* It would seem as if the salt 
of silver, being slightly afiected by the light, though not in a 
degree to produce any visible effect on it if alone, sets up a 
catalytic action, which is extended to the salts of iron, and which 

* The picture, when developed, is not readily injured by exposure to mo- 
derate light ; it ought, however, to be fixed, which may be done by washing it 
with a solution of bromide of potassium, fifteen or twenty grains to the ounce, 
iodide of potassium, five grains to the ounce. It may either be applied with a 
camel-hair-pencil or by immersion. The picture must then be well washed in 
water to remove the fixing material, which would cause it to fade by exposure 
to light. 


continues after the stimulus of the light is withdi-awTi. The 
catalysis which then takes place has induced me to name this 
process, for want of a better word, the Catalysotype. Sir* J. 
Herschel and Mr. Fox Talbot have remarked the same fact with 
regard to other salts of kon, but I do not know of any process 
being employed for photographic pui'poses, which depends on 
this action for its development, except my own. 

" My reason for using the mimatic solution previous to washing 
with the iodide of iron is this : I was for a long time tonnented 
by seeing the pictm-es spoiled by yellow patches, and could 
not remedy it, luitU I obseiwed that they presented an appear- 
ance as if that poi-tion of the nitrate of silver which was not de- 
composed by the iodide of iron had flowed away from the part. 
I then recollected that Sii' J. Herschel and Mr. Hunt had 
proved that iodide of silver is not veiy sensitive to light, unless 
some free nitrate be jDresent. I accordingly tried to keep both 
together on the paper, and after many plans had failed, I suc- 
ceeded by steeping it in the acid solution, which makes it fi-eely 
and evenly imbibe whatever fluid is presented to it. I am sure 
that its utility is not confined to this effect, but it was for that 
purpose that I fii'st employed it. 

" My reason for adding the tincture of iodine to the sjTup is, 
that having in my first experiments made use of, with success, 
a s}Tup that had been for some time prepared, and afterwards 
remarking that fresh spnip did not answer so well, I examined 
both, and foimd in the former a little free iodine ; I therefore 
added a little tinctm-e of iodine with much benefit, and now 
always use it in quantities proportioned to the age of the syrup. 
" The following liints will, I think, enable any experimenter to 
be successfid in producing good pictures by this process. In the 
fii'st place, the paper used should be that called wove post, or 
well-glazed letter paper. When the solutions are applied to it, 
it should not immediately imbibe them thoroughly, as would 
happen with the thinner sorts of paper. If the acid solution is 
too strong, it produces the very effect it was oi'iginally intended 
to ovei'come ; that is, it produces yellow patches, and the picture 
itself is a light brick coloiu- on a yellow gi-oimd. When the 
tincture of iodine is in excess, partly the same restxlts occiu* ; so 
that if this effect is visible, it shows that the oxide of sUver 
which is thrown down is partly re-dissolved by the excess of acid 
and iodine, and their quantities shoidd be diminished. On the 
contrary, if the silver solution is too strong, the oxide is depo- 
sited in the dark, or by an exceedingly weak Hght, and in this 
case blackens the yellow parts of the pictui'e, which destroys it. 
"WTien this effect of blackening aU over takes place, the silver so- 


lution should be weakened. If it be too weak, the paper ramains 
yellow after exposiu-e to ligbt. If the iodide of iron be used 
in too great quantity, the picture is dotted over with black spots, 
which afterwards change to white. If an excess of nitrate of 
silver be used, and a photograph immediately taken before the 
deposition of the oxide takes place, there ^vdll be often after some 
time a jjositive pictm-e formed on the back of the negative one. 
The excess of the nitrate of silver makes the paper blacker where 
the light did not act on it, and this penetrates the paper ; 
whereas the darkening produced by the light is confined to the 
sm-face. The maximum intensity of the spectinim on the paper, 
when a prism of crown glass is used, lies between the indigo and 
blue ray. The difference of eifect of a strong and weak light is 
beautifully sho^vn in the action of the spectrum : that pai-t of 
the paper which is exjiosed to the indigo ray is coloured a red- 
dish brown, and this is gradually darkened towards either ex- 
tremity, untn it becomes a deep black. 

" I have not had many opportnities of experimenting with 
the catalysotype, but it certainly promises to repay the trouble 
of ftu'ther investigation. The simplicity of the process, and the 
sensibility of the paper, should cause it to be extensively used. 
It has all the beauty and quickness of the calotype, without its 
trouble, and very little of its uncertainty ; and, if the more fre- 
quent use of it by me, as compared with other processes, does not 
make me exaggerate its facility of operation, I think it is likely 
to be practised successfiUly by the most ordinary experimenters." 
Dr. Woods subsequently made the following addition : — 

" Since the jireceding paper was wi-itten, I have been ex- 
perimenting with the catalysotype, and one day having had 
many failiu-es, which was before quite unusual with me, I am 
induced to mention the cause of them, for the benefit of sub- 
sequent experimenters. The paper I used was very stiff and 
liighly glazed, so that the solution fii'st applied was not easily 
imbibed. The blotting paper was very dry and biblulous. When 
using the latter, I removed nearly all the solution of iron from 
the first, and, of course, did not obtain the desii'ed residt. 

" While vaiying the process in endeavovu'ing to find out the 
cause just mentioned, I discovered that the following proportions 
gave veiy fine negative pictvu-es, from wliich good positive ones 
were obtained : — Take of syrup of iodide of u-on, distilled water, 
each two drachms ; tinctui-e of iodine, ten to twelve ch*ops : mix, 
Fii"st brush this over the paper, and after the few minutes, having 
dried it with the blotting paper, wash it over in the dark (before 
exposure in the camera) ^dth the follo\%Tng solution, by means 
of a camel-hail" pencil : — Take of nitrate of silver one drachm ; 


pure water one ounce : mix. This gives a darker picture than 
the original preparation, and consequently, one better adapted 
for obtaining positive ones ; it also requires no previous steeping 
in an acid solution. To &s. the pictiu-e let it be washed fii'st in 
water, then allowed to remain for a few niiautes in a solution of 
iodide of potassium (five gi-ains to the ounce of water) and washed 
in water again. The paper I use is the common vmglazed copy 
paper, but such as has a good body. I have tried the same 
paper ■v\-ith the original preparation, and find it to answer ex- 
ceedingly well ; it does not requii-e in this case, either, an acid 
solution. The same precautions and hints apply to the amended 
as to the original process ; such as, when it blackens in the dark, 
there is too much caustic used ; when it remaias yellow, or that 
it is studded with yellow spots, too much iodine ; wh.en marked 
with, black spots, too much iron. It is necessary to mention 
these, on account of the vai-ying strength of the mateiials em- 

Sectiox Y. — Ferroctaxide of Potassium. 

At the meeting of the Biitish Association at Plymouth in 
184:1, I fii^t dii-ected attention to the use of the ferrocyanide of 
potassiiun ia combiaation -«-ith the iodide of silver. The jjrocess 
resulting from this being very important in many points, the 
absti-act of the paper then read, as given in the Transactions of 
the Sections, is reprinted. 

The author having been engaged in experiments on those 
varieties of photogi-aphic di-a wings which ai-e formed by the action 
of the hychiodic salts on the dai-kened chloride of silver, and Tvith 
a view to the removal of the iodide formed by the process from 
the paper, was led to observe some peculiar changes produced 
by the combined influences of simshine and the ferrocyanide of 
potassium. It was found that the ordinary photogi-aphic paper, 
if allowed to darken in sunshine, and then slightly acted on by 
any hydiiodic solution, and, when cfry, washed ^dth a solution 
of the ferrocyanide of potassium, became extremely sensitive to 
Light, changing from a light brown to a friU black by a moment's 
exposui-e to simskine. Following out this result, it was dis- 
covered that pei-fectly pui-e iodide of silver was acted on with 
even gi-eater rapidity, and thus it became easy to form an ex- 
quisitely sensitive photogi-aphic paper. 

The method recommended is the following : — 

Highly glazed letter paper is washed over with a solution of 
one drachm of nitrate of silver to an ovince of distiUed water ; 


it is quickly di-ied, and a second time washed with the same so- 
hition. It is then, when diy, placed for a minute in a solution 
of two ch'achms of the iodide of potassium in six ounces of water, 
placed on a smooth board, gently washed by allowing some water 
to flow over it, and di-ied in the dark at common temperatures. 
Papers thus prepared may be kept for any length of time, and 
are at any time rendered sensitive by simply washing them over 
with a solution formed of one di-achm of the ferrocyanide of 
potassium to an ounce of water. 

These papers, washed "^dth the ferrocyanide and di'ied in the 
dark, are, in this diy state, absolutely insensible, but they may 
at any moment be rendered sensitive by merely washing them 
with a little cold clean water. 

Papers thus prepared are rendered quite insensible by being 
washed over with the above hydriodic solution. They are, how- 
ever, best seciu'ed against the action of time by a solution of 

Section YI. — The Fluorotype, 

So called from the introduction of the salts of fluoric acid, con- 
sists of the following process of manipulation : — 

( Bromide of potassium, 20 grains. 

\ Distilled water ... 1 fluid oimce. 

( Fluoride of sodium . 5 gi-ains. 

( Distilled water ... 1 fluid ounce. 

Mix a small quantity of these solutions together when the 
papers are to be prepared, and wash them once over with the 
mixture, and, when diy, apply a solution of nitrate of silver, 
sixty grains to the ounce of water. These papers keep for some 
weeks without injury, and become impressed with good images 
in half a minute in the camera. The impression is not suffi- 
ciently strong when removed from the camera for producing 
positive pictiu'es, but may be rendered so by a secondaiy process. 
The photograph should first be soaked in water for a few 
minutes, and then placed upon a slab of porcelain, and a weak 
solution of the proto-sulphate of iron brushed over it ; the 
picture almost immediately acquii-es an intense colour, which 
should then be stopped directly by pkmging it into water slightly 
acidulated with muriatic acid, or the blackening ■wall extend all 
over the paper. It may be fixed by being soaked in water, and 
then dipped into a solution of hypo-sulphite of soda, and again 
soaked in water as in the other processes. 


Mr. Bingliam has tlie following remarks on tliis process, and 
he gives a moditied form, into "which a new photographic element 
is introdiioed: — 

" We find it is better to add to the proto-snlphate of iron a 
little acetic or snlphui-ic acid : this will be found to prevent the 
darkening of the lights of the picture to a gi*eat extent, and it 
will be found better not to prepire the paper long before it is 
required for iTse, this being one reason why the picture often 
becomes dusky on application of the proto-siilphate. 

" Reasoning upon the principle that the action of Ught is to 
reduce the salts of sUver in the paper to the metaUic state, and 
that any substance which would reduce silver woidd also quicken 
the action of light, we were led to the following expei-iment : — 
The protochloride of tin possesses the property of reducing the 
salts both of silver and of gold : a paper was prepared with the 
bromide of silver, and previously to exposing it to light it was 
washed over with a veiy weak sokxtion of the chloride of tin ; 
the action of light upon the paper was exceedingly energetic ; 
it was almost instantaneously blackened, and a copy of a print 
was obtained in a few seconds." 

The use of fliiorides has been recently introduced as a novelty 
by some French jjhotogi-aphers, but reference to the author's 
Researches on Light, published in 1844, will distinctly show 
that I was the fii-st to employ these salts, as photographic agents. 

SECTIO^' XI* — Bro^hde of Silver a>'d Mercxtrial Yapoltj. 

In my first publication on this subject, in Griffin's Scientific 
Miscellany, I introduced the following process, which, although 
it has never yet been properly worked out, involves many points 
of interest : — Some extremely curious residts, led me to examine 
the efiect of the merciuial vapour on the piu-e precij)itated 
iodides and bromides. 1 was long perplexed with exceedingly 
anomalous results, but being satisfied fi'om particular experi- 
ments that these researches promised to lead to the discovery 
of a sensitive preparation, I persevered. 

To prepare this sensitive paper we proceed as follows : — 
Select the most perfect sheets of well-glazed satin post, quite free 
from specks of any kind. Placing the sheet carefully on some 
hard body, wash it over on one side by means of a very soft 
camel's hafr pencil, with a solution of sixty grains of the bromide 
of potassium, in two fluid ounces of distilled water, and then diy 
it qtiickly by the fire. Being cby, it is again to be washed over 


with tlie same solution, and cliied as befoi'e. Now, a solution of 
nitrate of silver, one hundi'ed and twenty grains to the fluid 
ounce of distilled water, is to be applied over the same surface, 
and the paper quickly dried in the dark. In this state the 
papers may be kept for use. When they are requii-ed, the above 
solution of silver is to be plentifully applied, and the paper 
placed icet in the camera, the greatest care being taken that no 
day-light, not even the faintest gleam, falls upon it, until the 
moment when we are prepared, by removing the screen, to per- 
mit the light, radiated from the objects we wish to copy, to act 
in producing the picture. After a few seconds, the light must 
be again shut off, and the camera removed into a dark room. 
It will be fotmd, on taking the paper ft-om the box, that there is 
but a very slight outline, if any, as yet visible. Place it aside, 
ia. perfect darkness, until quite dry, then fix it in a mercurial 
vapoiu- box, and apply a very gentle heat to the mercury. The 
moment the merciuy vaporizes, the pictiu-e will begin to develope 
itself The spirit lamp must now be removed for a short time, 
and when the action of the mercmy appears to cease, it is to be 
very carefully applied again, iintil a well-defined picture is 
visible. The vaporization must now be suddenly stopped, and 
the photogi'aph removed fr-om the box. The diuwing will then 
be very beautiful and distinct ; but much detail is still clouded, for 
the develojDment of which it is only necessary to place it cau- 
tiously in the dark, and allow it to remain vmdistiu'bed for some 
hours. There is now an inexpressible charm about the picture, 
equalling the delicate beauty of the daguerreotypes ; but beiag 
still very susceptible of change, it must be viewed by the light 
of a taper only. The nitrate of silver must now be removed 
from the paper by well washing in soft water. When the 
picture has been di-ied, wash it quickly over with a soft brush, 
dipjDed in a wai-m solution of the hyposidphite of soda, and then 
w^ell wash it for some time in the manner dii-ected for the 
ordinaiy photogi'aphs, in order that all the hyposidphite may be 
removed. The di-awing is now fixed, and we may use it to 
procure positive pictures, many of which may be taken from one 

Section VII. — Positive Photographs by One Process. 

About the same time Mr. Talbot, Sir- John Herschel, Dr. Fife, 
and myself, discovered the veiy remarkable property of the 
iodides iu bleaching the darkened salts of silver. Many very 
beautiful results may be thus obtaiaed. The manipulatory 


details published by Dr. Fife were simple in their- character, but 
arrived at by a long series of inqviiries. It is now quite easy to 
prepare photographic papers, on which the iodine solutions shall 
act ^vith perfect uniformity : — 

Soak the paper for a few minutes in phosphate or mui'iate of 
soda, removing -wdth a soft bi-ush any aii' bubbles which may form 
on it. The supei-flvious moistui'e must be wiped off with very clean 
cotton cloths, and the papers dried at common tempei'atm-es. 
When dry, the paper must be pinned out on a board, and the 
sUver solution spi-ead over it, boldly but lightly, with a veiy 
soft sponge brush. It is to be instantly exjDOsed to sunshine, 
and, if practicable, carried into the open aii', as the more speedily 
evaporation proceeds the less does the silver penetrate the 
paper, and the moi*e delicate it is. The fii-st surface is very 
irregular, being as before described, and represented in fig. 2. 
As soon as the siu'face appears dry, the silver solution must be 
again aj^plied as before, and the exposure repeated. It must 
now be exposed imtil a fine chocolate-brown colour is produced 
equally on all parts of the surface, and then, vmtil requii-ed 
for use, be carefully preserved fi"om the further influence of 
light. If the paper is to be kept long, the darkening must 
not be allowed to proceed so far as when it is to be speedily 
made use of. 

In darkening these papers, the greatest possible attention 
must be paid to the quantity of light to which they are sub- 
mitted, evex-thing depending on the rapidity of the blackening 
process. The morning sun should be chosen, for the reasons 
before stated. A perfectly cloudless sky is of great advantage. 
The injurious consequence of a cloud obscui'ing the sun during 
the last darkening process, is the formation of a siuface which 
has the appearance of being washed with a dii-ty brush. This 
is with difficidty removed by the iodides, and the resulting 
pictures want that clearness which constitutes their beauty. 
Papers darkened by the diffused light of a cloudy day are 
scai-cely, if at all, acted on by these salts. Great care must be 
taken to prevent the silver solution from flowing over the edges 
of the paper, as thereby an extra quantity of darkened silver is 
formed on both sides, which requires a long-continued action of 
the iodides and sunshine to bleach. 

The kind of paper on which the silver is spread is an object 
of much importance. A paper known to stationers as satin 
post, double-glazed, bearing the mark of J. Whatman, Turkey 
Mill, is decidedly siiperior to every other kind I have tried. The 
dax'k specks which aboimd in some sorts of paper must be 
avoided, and the spots made by flies veiy carefully guarded 


against. These are of small consequence diu-ing the darkening 
process, but when the bleaching wash is apjilied, they form 
centres of chemical action, and the whitening process goes on 
aroimd them, independently of light, deforming the drawing 
with small rings, which are continually extending theii* diameters. 
The saline washes may be considerably varied, and combined 
to an indefinite extent, with a continued change of efiect, which 
is smgularly interesting. In theii* apj^lication we shoidd be 
guided, as in the negative jjrocess, by their combining propor- 
tions. The following list of the salts which will give the best 
effects, selected from upwards of seven himdi'ed combinations, 
will show the variety of coloui-s produced. They are placed in 
the order of the sensitiveness they appear to maintain, when 
used as nearly as possible imder the same circumstances : — 

Colour of Picture. 
Muriate of Ammonia. . Red, changing to black in the sunshine. 

Chloride of Sodium Ditto, ditto. 

Chloride of Strontium A fine brown. 

Chloride of Barium ...A rich brown, inclining to 2Jurple. 

Sol. Chloride of Lime Very red. 

Sol. Chloride of Soda A brick red. 

Iodide op Potassium. . . . Yelloivish broivn. 

Chloride of Potas- f Variable, sometimes yellowish, ofien a 

siUM \ steel blue. 

Phosphate of Soda Mouse colour. 

Tartrate of Soda Bark brown. 

Urate op Soda Yelloioish broivn. 

Chloride of Iron Deep broion, lohich blackens. 

Bromide of Sodium Med brown of a p)ecidiarly rich tint. 

The change mentioned in the colour of the finished pictm-e 
is that which arises from a fresh exposure to the solar rays ; 
where no change is mentioned, it is too slight to be worth notice. 

When papers prepared with any of the above, except the 
phosphates, are soaked for a Little time in water, and di-ied in 
the svmshine, the picture produced, — it matters not what 
iodide is used, — is rendered peculiarly red, and does not change 
by re-exposm"e. By washing some of the papers with weak 
solution of ammonia, this peculiarity is produced in a very 
striking maimer. 

In the other divisions will be foimd some farther remarks on 
the very pecuHar physical phenomena presented by the action 
of the compounds of iodine on these darkened salts of silver, and 
details of yet more perfect forms of manipidation. 


Section VIII. — On the Application of the Daguerreotype 
TO Paper. 

The expense and. inconvenience of metallic tablets rendered 
it in the highest degree desirable that paper should be employed 
in theii' place. A very extensive series of experiments at length 
led to the pleasing conclusion of being enabled to prepare a 
paper which answered in every respect as well as the silver 
plates, and in many much better. 

This discovery formed the subject of a commimication to the 
Royal Society, which that learned body did me the honoui* to 
print in their Transactions. My memoir is entitled, — " On the 
Influence of Iodine in rendering several Argentine Compounds, 
spread on Paper, sensitive to Light ; and on a New Method of Pro- 
ducing, with greater distinctness, the Photographic Image." This 
paper contains the substance of the follo^ving remarks ; but 
since the publication of the Transactions I have been successful 
in simplifying the process of prejoaration. 

My experiments established, in the most satisfactoiy manner, 
that even on the silver talilets a semi-oxidized sm'face was j^re- 
sented to the iodine. They also proved that perfectly pure 
iintarnished silver was by no means readily acted on by the 
iodine. From this I was led to prepare oxides of silver in many 
different ways, which enabled me to spread them over paper, 
and the residt was instiiictive. Any of the ordinary photo- 
graphic papers allowed to darken to a fiill brown, which is a 
stage of induced oxidation, become, by long exposvire to iodine, 
of a steel-blue or violet colour. If exposed in this state to 
sunshine for a long period, their coloiu^ changes fi'om gi'ay to a 
clear olive. Now, exposui'e to sunshine for a minute, or to dif- 
fused daylight for five minutes, produces no ctpparent change ; 
but mercui'ial vapour speedily attacks the portions which have 
been exposed to light, and a faitlifid picture is given of whatever 
may have been superposed. There is, however, a want of suffi- 
cient conti*ast between the lights and shadows. By allo-wang 
the first darkening to proceed until the paper acquires the olive 
colour, which indicates the formation of a time oxide of silver, 
it wiU be found, although it is not more speedily acted on 
by the iodine, that it is more sensitive, and that a better 
pictui'e is formed. The kind of photographic preparations used 
appears to have but little influence on the resiUts, — a chloride, 
iodide, or bromide of silver, allowed to darken, answers equally 

There are many things, xmfortimately, which prevent oui" 


availing oui'selves of tliis easy metliod of producing a tolerably 
sensitive Dagnen-eotype paper. These are, certain in-egular 
formations of oxides in different states, and the revival of 
metallic silver in some parts of the siu-face. 

I next spread papers with the pxu-e oxide formed by chemical 
means, and also the protoxide, and many of its salts. These 
papei's were not veiy readily affected by iodine, or influenced by 
light dui'ing short exposiu-es. 

Silver is revived fi-om its solutions by hydrogen gas ; conse- 
qently, nothing is more easy than, by washing a paper ^\^th 
nitrate of silver in solution, to procure a fine silver paper, by 
passing a cuiTent of hydrogen gas over it. 

A pictiu-e of a peculiarly delicate character may be produced 
on this kind of paper ; but it has not the required sensibility, 
and there is a great want of contrast in the lights and shadows. 
It may be interesting to state, that the yellow-brown phosphate 
of sUver is as readily acted on by iodine as the oxides, and is 
quite as sensitive to luminous influence. Phosphuxetted hydrogen 
gas effects the revival of metallic silver, and the sui'face produced 
by means of this gas, used as the hydrogen was in the former 
case, is of a fine steel-blue, which coloui* arises firom a portion 
of phosphorus having entered into combination with the silver. 
These kinds of paper comported themselves in eveiy respect 
as the metallic tablets — were equally sensitive, and produced 
pictures as deKcately beautiful. Unfortiinately, however, owdng 
to the spontaneously inflammable natm-e of the phosphuretted 
hydrogen gas, it is not safe to operate with it. After various 
ineffectual contrivances to overcome this difficulty, I was obliged 
to abandon the iise of this gas entu-ely — warned of the danger 
I incui-ed, — by several violent but fortunately harmless explo- 
sions. The vapour of phosphorus and of sulphur was also tried, 
and many very beautiful effects were produced. At length, 
however, I stopped at sulphuretted hydrogen, which answers 
in eveiy respect.* 

To prepare this, soak a paper of veiy fii-m textm-e, not too 
much glazed, in a weak soliTtion of the muriate of ammonia. It 
must then be wiped with clean cloths, and carefully dried. The 
paper is then dipped into a weak solution of the nitrate of silver, 
and the small bubbles which form on its surface are carefully 
removed with a camel's hair pencil. When the paper is nearly, 
but not quite, diy, it must be exposed in a closed vessel to sul- 

A very interesting account of the revival of gold and silver from their solu- 
tions by these gases, will be found in a tract on Combustion, published by Mrs. 


phiu'etted hydrogen gas, slowly foiined fi'om the suljihiiret of 
antimony and hydrochloric acid : in a few minutes it will become 
of an iron-brown colour, hav^ing a fine metallic lustre. It is 
again to be passed through a solution of silver, somewhat stronger 
than the first, and dried, taking care that no shadow falls on 
the paper whilst it is chying. It is then a second time sub- 
mitted to sulphuration, and, by careful management, the process 
is now generally completed. If, howevei', the paper is not 
considered to be sufficiently dark, it mi;st be once more washed 
in the solution of silver, and again subjected to the action of 
sulphuretted hydi-ogen. 

If the above paper be allowed to remain in the sulphui-etted 
hydi'ogen gas after the maximiim blackness is produced, it is 
again whitened with some quickness. This may be accounted 
for in two ways : the gas may be mixed with a portion of 
muriatic acid vapoiu", or a quantity of chlorine sufficient to pro- 
duce this efiect may be liberated from the preparation on the 
paper to react on the sulphm*et of silver. 

The perfection of these papers consists in ha'sang a deep black 
groxmd to contrast with the merciu'ial deposit, by which means 
the pictures have the advantage of being seen equally well in all 
^Dositions, whereas Daguerre's pictiu'es on the metal plates can 
only be seen to advantage at certain angles. 

The sulphuretted paper may be rendered sensitive in the 
same manner as the plates by exposui-e to the vapour of iodine. 
I, however, prefer di-awing the paper over a solution thus 
formed : — A saturated solution of any salt of iodine is made to 
dissolve as much pure iodine as possible, and of this liquid two 
di-achms are mingled with foui- ounces of water. Care is re- 
quii'ed that one side only of the paper is wetted, which is by no 
means difficult to efiect, the fluid is so greedily absorbed by it ; 
all that is necessary being a broad shallow vessel to allow of 
the paper touching the fluid to its fuU "nddth, and that it be 
drawn over it with a slow steady movement, ^Tien thus 
wetted, it is to be quickly dried by a warm, but not too bright 
fire ; of course daylight mxist be carefully excluded. Papers 
thus iodidated do not lose their sensitiveness for many days if 
cai'efitlly kept from Hght. 

On examining the sheet after the Daguerreotype processes in 
the camei*a, and of mercimalization, have been completed, a very 
perfect pictiu-e is found upon it ; but it is still cajmble of vast 
improvement, which is, by the follo'ndng simple plan, accom- 
plished in a way which is at once magical and beautifril. 

Action of Corrosive Sublimate.— Dip one of the Daguen-eo- 
type pictiu'es, formed on the sulphui-etted paper, into a solution 


of coiTosive sublimate : the drawing instantly disappears, but, 
after a few minutes, it is seen unfolding itself, and gradually 
becoming far more distinct than it was before ; deKcate lines, 
before invisible, or barely seen, are now distinctly marked, 
and a rare and singular perfection of detail given to the 
drawing. It may appear, at first sight, that the bichloride 
of mercury dissolves off the metal, and again deposits it in 
the form of chloride (calomel). But this does not account 
for the fact, that if the paper has been pre^iared with the nitrate 
of silver, the mercury disappears, and the drawing vanishes, the 
deposit taking place only on those parts upon which light has 
acted but feebly ; as, for instance, on the venations of leaves, 
leaving those portions of sui-face which were exposed to full 
luminous influence wdthoxit a particle of qvucksilver. When the 
I^aper has been either a chloride or iodide, the effect is as above, 
and the thickness of the deposit is as the intensity of the light 
has been ; consequently, the semi-tints ai-e beautifully preserved. 
If the di-awdng remains too long in the solution, the precipitate 
adheres to the dark parts and destroys the effect. The singvda- 
rity of this operation will be more striking if the pictiu-e has 
been soaked some time in the solution of the hyposuljjhite of 
soda, and then dipped into the bichloride of mercmy. As the 
dra^ving disappears, a series of circles, formed of a white powder, 
appear to arise from the paper, generally commencing at the 
centre, and slowly extending over the whole surface : the powder 
is afterwards deposited, and the sheet is buried in the precipi- 
tate ; but on taking the paper from the liquid, and passing a 
stream of water over it, the precipitate is entii'ely removed from 
all the i^arts excejit the lights of the picture. I have also foxmd 
the invisible jshotographic image become evident, without the 
aid of mercurial vapour, by simply soaking for some time in a 
solution of corrosive sublimate. 

When these papers are prepared with due care, they are ex- 
tr-emely sensitive, and if used for copying engravings diu-ing 
bright sunshine, the efiect is instcaitaneous. The great difficulty 
is to present the paper to the sun, and withdraw it with sujfi- 
cient celerity. In the weak light of the camera a few minutes 
during sunshine is quite sxifiicient for the jiroduction of the best 
effects. One gi-eat advantage of these pictures over those pro- 
cm-ed on the plated copper is, that the merciuy does not lie 
loosely as on the tablets, but is firmly fixed, being absorbed by 
the paper ; therefore these pictures may be kept without injiuy 
in a portfolio. 

If, instead of immersing the paper in a vessel ftdl of sulphu- 
retted hych'ogen gas, a stream of the gas is made to j^lay upon it, 


it asstimes a most richly iridescent siu-face ; tlie A*arious coloiu-s 
are of difierent degrees of sensibility, but for siu-face di-awings 
they may be used ; and in copying of leaves or flowers, beautiful 
pictui'es, which appear to glow with the natiu'al coloui"s, are 

Section IX. — Salts of Gold as Photographic Agents. 

It is well known that gold is revived from its ethereal solution 
by the action of light, and that the same effect takes place when 
the nitro-miu-iate of gold is spread on charcoal. We are mainly 
indebted to Hei-schel's paper, published in 1840, for the know- 
ledge we possess of gold as a photogTapliic agent. 

Considering it probable that the requii'ed unstable equilibrium 
might be induced in some of the salts of gold, I was induced to 
pm'sue a great many experiments on this point. In some cases, 
where the pajier was impregTiated with a mordant salt, the salt 
of gold was darkened rapidly, without the assistance of light ; 
in others, the effect of light was very slow and uncertain. By 
washing paper with muriate of barytes, and then with a solution 
of the chloride of gold, a paper, having a slight pinky tint, is 
procui'ed ; by exposiag this paper to sunshine it is at fij'st 
whitened, and then, but very slowly, a darkening action is in- 
diiced. If, however, we remove the paper from the light, after 
an exposure of a few minutes, when a very faint impression, and 
oftentimes not any, is apparent, and hold it in the steam of boil- 
ing water', or immerse it in cold water, all the pai-ts which were 
exposed to the light are rapidly darkened to a full piu-jjle brown, 
leaving the covered portions on which the light has not acted, 
a pure white, producing thus a fine negative ch-awing. If, while 
such a paper, or any other paper, prepared with the chloride of 
gold, is exposed to the sun, we wash it with a weak solution of 
the hydriodate of potash, the oxidation is very i-apidly broxight 
on, and the darkness produced is much greater than that ob- 
tained by the other method ; but this plan is not often applicable. 
I have not yet been enabled to produce Avith the salts of gold 
any paper which should be sufficiently sensitive for use in the 
camera obscura. 

Sir John Hei-schel devoted much attention to the examination 
of the salts of plantinum as well as gold. He found plantinum 
under nearly all circumstances veiy little sensitive to Kght, but 
the following were the results obtained^vith the salts of gold: — 

If paper impregnated vdih oxalate of ammonia be washed with 
chloride of gold, it becomes, if certain proportions be hit, pretty 


sensitive to light ; passing rather rapidly to a violet piu-ple in 
the sun. It passes also to the same piu'ple hue in the dark, 
though much more slowly; so that, as a photographic combina- 
tion, it is useless. 

Paper impregnated with acetate of lead, when washed with 
perfectly neutral chloride of gold, acquires a brownish-yellow 
hue, and a sensibihty to light, which, though not great, is at- 
tended with some peculiarities highly worthy of notice. The 
first impression of the solar rays seems rather to whiten than to 
darken the paper, by discharging the original coloiu', and sub- 
stituting for it a pale grayish tint, which by slow degrees in- 
creases to a dark slate coloui-. But if arrested while yet not 
more than a moderate ash gray, and held in a current of steam, 
the colour of the part acted on by the sunshine, and that only, 
darkens immediately to a deep piu'ple. The same effect is pro- 
duced by immersing it in boiling water. If plunged in cold 
water, the same change comes on more slowly, and is not com- 
plete till the paper is cMed by heat. A dry heat, however, does 
not operate tliis singular change. 

If a neuti'al solution of the chloride of gold is mixed with an 
equal quantity of the solution of bichromate of potash, paper 
washed with this solution, and exposed to light, speedily changes, 
fii-st to a deep broA\'n, and ultimately to a bluish black. If an 
engraving is superposed, we have a negative copy, blue or brown, 
upon a yellow gi-ound. If this photograph is placed in clean 
water, and allowed to remain in it for some hoiu's, veiy singular 
changes take place. The yellow salt is all dissolved out, and 
those parts of the paper left beautifidly white. All the dark 
portions become more decided in their character, and according 
as the solarizatiou has been prolonged or otherwise, or the light 
has been more or less intense, we have either crimson, blue, 
brown, or deep black negative photographs. 

Section X. — The Influence of Chlorine and Iodine in 


Having on many occasions subjected the simply nitrated pho- 
tographic paper to the influence of chlorine and iodine in close 
wooden boxes, I was often struck with the sudden change which 
light prodviced on the wood of the box, particiilarly when it was 
of deal ; changing it in a few minutes from a pale yellow to a 
deep green. This curious effect frequently occiu-ring, led me to 
observe the change somewhat more closely, and to pursue some 


experiments on the subject. These produced no very satisfac- 
toiy result. They proved the change to depend much on the 
formation of hydrochloric and hych-iodic acids, and the decom- 
position of water in the pores of the wood. I found well-baked 
wood quite insusceptible of this very curious phenomenon. The 
woods of a soft kind, as the deal and willow, were much sooner 
influenced than the harder varieties, but all the light-coloui'ed 
woods appeared more or less capable of undergoing this change. 
All that is necessary is, to place at the bottom of an air-tight 
box, a vessel containing a mixtm-e of manganese and muriatic 
acid, or simply some iodine, and fix the piece of wood at some 
distance above it. Difierent kinds of wood requii-e to be more 
or less saturated with the chlorine or iodine, and consequently 
need a longer or shorter exposm-e. The time, therefore, neces- 
saiy for the wood to remain in the atmosphere of chlorine can 
only be settled by direct experiment. Wood is impregnated 
very readily with iodine, by putting a small portion in a capsvde 
a few inches below it. It does not appear to me at jjresent that 
any practical result is likely to arise out of this peculiar pro- 
perty ; it is only introduced as a singular fact, which is perhaps 
worthy a little attention. 



To Sir John Herschel we are indebted for tlie first use of glass 
plates to receive sensitive photogi-aphic films. 

Section I. — Precipitates of Silver Salts. 

The interest which attaches to this is so great, and there 
appear to be in the process recommended by the English experi- 
mentalist so many suggestive points, fi.-om which fiitvu-e j^hoto- 
gi-aphists may start, that the passages are given in Sii' John 
Herschel's o'wti words : — 

" With a view to ascertain how far organic matter is indis- 
pensable to the rapid discoloration of argentine compounds, a 
process was tried which it may not be amiss to relate, as it issued 
in a new and veiy pretty variety of the photograpliic art. A 
solution of salt of extreme dilution was mixed with nitrate of 
silver, so dilute as to form a liquid only slightly milky. This 
was poui'ed into a somewhat deep vessel, at the bottom of which 
lay horizontally a very clean glass plate. After many days the 
greater part of the liquid was decanted ofi" with a siphon tube, 
and the last portions very slowly and cautiously draiaed away, 
drop by di-op, by a siphon composed of a few fibres of hemp, 
laid pai-aUel and moistened without twisting. The glass was 
not moved till quite diy, and was fotind coated with a pretty 
uniform film of chloride of silver, of delicate tenuity and che- 
mical pvuity, which adhered with considerable force, and was 
veiy little sensitive to light. On cbopping on it a solution of 
nitrate of silver, however, and spreading it over by inclining the 
plate to and fro (which it bore without discharging the film of 
chloride) it became highly sensitive, although no organic matter 
could have been introduced -wdth the nitrate, which was quite 
pure, nor coidd any indeed have been present unless it be sup- 
posed to have emanated from the hempen filaments, which were 
bai'ely in contact %\ith the edge of the glass, and which were 


constantly abstracting matter from its surface in place of intro- 
ducing new. 

" Exposed in this state to the focus of a camera with the glass 
towai'ds the incident light, it became impressed with a remark- 
ably well-defined negative pictiu-e, which was direct, or reversed, 
according as looked at from the front or the back. On pouring 
over this cautiously, by means of a pipette, a solution of hypo- 
sulphite of soda, the picture flisappeax'ed, but this was only while 
wet ; for on washing in pure water and drying, it was restored, 
and assvuned much the air of a dagueiTeotype when laid on a 
black groimd, and still more so when smoked at the back, the 
silvered portions reflecting most light, so that its characters had, 
in fact, changed from negative to positive. From such a pic- 
ture (of course before smoking) I have found it practicable to 
take photogi-aphic copies ; and although I did not, in fact, suc- 
ceed in attempting to thicken the film of silver, by connecting 
it. Tinder a weak solution of that metal, with the reducing pole 
of a voltaic pile, the attempt afibrded distinct indications of its 
practicability with patience and perseverance, as here and there, 
over some small portions of the sm-face, the Kghts had assumed 
a full metallic brilliancy tmder this process. I would only men- 
tion further, to those who may think this experiment worth 
repeating, that all my attempts to secure a good result by diy- 
ing the nitrate in the film of chloride have faded, the crystalliza- 
tion of the salt disturbing the uniformity of the coating. To 
obtain delicate pictm-es the plate must be exposed wet, and when 
withdi-awn must immediately be plunged into water. The 
rdtrate being thus abstracted, the plate may then be dried, in 
which state it is half fixed, and it is then ready for the hypo- 
sulphite. Such details of manipulation may appear minute, but 
they cannot be dispensed with in pi-actice, and cost a gi'eat deal 
of time and trouble to discover, 

" This mode of coating glass with films of precipitated argen- 
tine or other compoimds, afibrds, it may be observed, the only 
efiectual means of studj-ing then- habitudes on exposui-e to light, 
free from the powerful and ever-vaiying influence of the size in 
paper, and other materials used in its manufactm-e, and estimat- 
ing thefr degree of sensibility and other particidars of their 
deportment under the influence of reagents. I find, for example, 
that glass so coated with the iodide of silver is much more sen- 
sitive than if similarly covered with the chloride, and that if 
both be washed with one and the same solution of nitrate, there 
is no comparison in respect of this valuable quality; the iodide 
being far superior, and of coiu-se to be adopted in preference for 
the use of the camera. It is, however, more difficult to fix:, the 


action of the hyposulpliites on this compound of silver being 
comparatively slow and feeble. 

" When the glass is coated %vith the bromide of silver, the action, 
per se, is very slow, and the discoloration ultimately produced 
far short of blackness ; but when moistened with nitmte of silver, 
sp. gr. ri, it is still more rapid than with the iodide, tui'ning 
quite black in the covu-se of a very few seconds' exposure to 
sunshine. Plates of glass thus coated may be easily preserved 
for the use of the camera, and have the advantage of being ready 
at a moment's notice, requiring nothing but a wash over with 
the nitrate of silver, which may be delayed imtil the image is 
actually thrown on the plate, and adjusted to the coi-rect focus 
with all deliberation. The sensitive wash being then applied 
with a soft flat camel-hau* brush, the box may be closed and the 
picture impressed, after which it only requires to be thrown into 
water, and dried in the dark, to be rendered comparatively in- 
sensible, and may be finally fixed with hyposidphite of soda, 
which must be applied hot, its solvent power on the bromide 
being even less than on the iodide." 

Sir John Herschel suggested a trial of the fluoride of silver 
aipon glass, w^hich, he says, if proved to be decomposable by 
light, might possible efiect an etching on the glass, by the cor- 
roding property of the hydrofluoric acid. 

The metallic fluorides have been found to be decomposable, 
and a veiy sensitive process on paper, called the fluorotype, will 
be described in the chapter on Miscellaneous Processes. I am 
not aware that any experiments have been made dii-ectly upon 
glass, but it is certainly worthy of a careful trial. 

Herschel has remarked that we cannot allow the wash of 
niti-ate to dry upon the coating of the chloride or iodide of silver. 
If, however, we dip a glass which has one film of chloride upon 
it into a solution of common salt, and then spread upon it some 
nitrate of silver, we may veiy materially thicken the coating, 
and thus produce more intense efiects. IVIr. Towson employed plates prepared in this manner with much success. The 
mode adopted by that gentleman was to have a box the exact 
size of the glass plate, in the bottom of which was a smaU hole ; 
the glass was placed over the bottom, and the mixed solution, 
just strong enough to be milky, of the salt and silver poui-ed in. 
As the fluid finds its way slowly arovmd the edges of the glass, 
it filters out ; the pecidiar surface action of the solid glass plate, 
probably a modified form of cohesive force, separating the fine 
precipitate, which is left behind on the sm-face of the plate. By 
this means the operation of coating the glass is much quickened. 
Another method by which films of any of the salts of silver can 



be produced VL])on glass plates, is tlie modification of 
the patent processes of Di"ayton and of Thompson for silvering 
glass: — 

Take a very clear plate of glass, and having put around it an 
edging of wax about haLf-an-inch in depth, poiu- into it a solu- 
tion of niti'ate of silver made alkaline by a few di-ops of am- 
monia, taking care that no oxide of silver is precipitated ; mix 
with this a small quantity of spirits of wine, and then add a mix- 
ture of the oils of lavender and cassia, or, which is perhaps the 
best process, a solution of gi'ape sugar. In a short time the 
glass will be covered Avith a veiy beautiful metallic coating. The 
solution is now poiu'ed oft", the edging of wax removed, and the 
silver is exposed to the action of diluted chloi-ine, or to the vapour 
of iodine or bromine, until it is converted into a compound of one 
of these elements, after which we may proceed as recommended 
by Sir John Herschel. 

Section II. — Albumen. 

In the Technologiste for 1848, M. Is'iepce de Saint- Victor 
published his mode of applying albumen to glass plates. M. 
Blanquart Evei-ard followed, and successively albumen, gelatine, 
and serum were employed. Messi-s. Eoss and Thomson, of 
Edinbm-gh, have been eminently successftJ operatoi-s with 
albumen on glass plates, many of their pictvu-es leaving little to 
be desired. The manipulatory details of the albumen process 
will be found in the technical division of this work. 

Section III. — Collodion. 

The successful application of a solution of gun-cotton in 
ether, to form the film for receiving the sensitive sivrface on 
glass, has been claimed respectively by Mr. Fiy and 'Mr. Archer. 
There is some difficulty in fixing precisely this point, since there 
was no actual publication of the process until long after it was 
generally in use. Mr. Fiy certainly introduced the use of gutta 
percha in combination with collodion. 

The last novelty to which reference need be made is the icax 
paper process of M. Le Gray, which will be fully described. 



When Dagiien-e published his pi"ocess, a period of twenty 
minutes was reqiiii'ed to obtain a good copy of any external 
object : hence this period was far too long to admit of its being 
employed for portraiture. 

Mr. Towson, of Devo?ipoi-t, in a veiy raluable paper wliich 
appeared in the Philosopliical Mayazine in 1839, offered several 
suggestions on the use of large lenses, <tc., which he sup^Dosed 
might lead to the use of the daguerreotype for the pui-poses of 

Dr. Draper, of New York, acting on the suggestions of Mr. 
Towson relative to the adjustment of the focus, succeeded in 
accelerating his process so far as to obtain portraits from the 
life. He published his process in the London and Edinburgh 
Philosophiccd JfagaciJie for September 1840. From this paj3er 
I shall take the liberty of making copious extracts. It was 
first stated that it was necessaiy, to procure any impression of 
human features on the daguerreotype plate, to paint the face 
white, or dust it over with a white powder, it being thought that 
the light reflected from the flesh would not have sufiicient jDower 
to change the iodized surface. This has been shown to be an 
error, for, even when the sun shines but dimly, there is no 
difficulty in obtaining a connect delineation of the featiu-es. 

"When the sun, the sitter, and the camera, are situated in 
the same vertical plane, if a double convex non-achromatic lens 
of four inches diameter and foiu-teen inches focus be employed, 
jjerfect miniatures can be prociu-ed in the open air in a period 
varying with the character of the Kght from 20 to 90 seconds. 
The dress also is adminibly given, even if it should be black ; 
the slight difierences of illumination are sidficient to characterize 
it, as well as to show each button and button-hole, and every 
fold. Partly owing to the intensity of such light, which cannot 
be endiu'ed without a distortion of the featm'es, but chiefly 
owing to the cii'cmnstance that the rays descend at too gTcat 
an angle, such pictiu-es have the disadvantage of not exhibiting 
the eyes with distinctness, the shadow from the eyebrows and 
forehead encroaching on them. To procm-e fine proofs, the best 
position is to have the Line joining the head of the sitter and 


the camera so arranged as to make an angle with the incident 
Tays of less than ten degrees, so that all the space beneath the 
eyebrows shall be illuminated, and a slight shadow cast from 
the nose. This involves, obviously, the use of reflecting mirrors 
to direct the ray. A single mirror would answer, and would 
economise time, but in practice it is often convenient to employ 
two ; one placed, with a suitable mechanism, to direct the rays 
in vertical lines, and the second above it, to direct them in an 
invariable course towards the sitter. 

" On a bright day, and with a sensitive plate, portraits can be 
obtained in the course of five or seven minutes, in the diffused 
day-light. The advantages, however, which might be supposed 
to accrue from the features being more composed, and of a 
natm'al aspect, are more than counterbalanced by the difficulty 
of retaining them so long ia one constant mode of expression. 
But in the reflected sunshine, the eye cannot bear the effulgence 
of the rays. It is therefore absolutely necessary to pass them 
through some blue medium, which shall abstract from them 
their heat and take away theu* offensive brilliancy. I have used 
for this purpose blue glass, and also ammoniaco-sulphate of 
copper, contained in a large trough of plate glass, the intei'stice 
being about an inch thick, and the fluid diluted to such a point, 
as to permit the eye to bear the light, and yet to intercept 
no more than was necessaiy. It is not requisite, when coloured 
glass is employed, to make use of a large surface ; for if the 
camera operation be carried on untU the proof almost solarizes, 
no traces can be seen in the portrait of its edges and boun- 
daries ; but if the process is stopped at an earlier interval, there 
will be commonly found a stain coiTesponding to the figure of 
the glass." 

"The chair in which the sitter is placed has a staff at its 
back, terminating in an iron ring, that supports the head, so 
arranged as to have motion in directions to suit any stature 
and any attitude. By simply resting the back or side of the 
head against this ring, it may he kept sufficiently still to allow 
the minutest mai'ks on the face to be copied. The hands should 
never rest upon the chest, for the motion of respiration disturbs 
them so much as to bring them out of a thick and ckmisy 
appearance, destroying also the representation of the veins on 
the back, which, if they are held motionless, are copied with 
surprising beauty. 

" It has already been stated, that certain pictorial advantages 
attend an arrangement in which the light is thrown upon the 
face at a small angle. This also allows us to get rid entirely of 
the shadow fi-om the background, or to compose it more grace- 



fully in the picture ; for this, it is weU that the chair should be 
brovight from the back-ground, from three to six feet. 

"Those who undertake daguerreotype portraitvires will of 
course arrange the back-grounds of their pictiu'es according to 
their own tastes. When one that is quite imiform is required, 
a blanket, or a cloth of a ch-ab coloui', properly suspended, will 
be found to answer very well. Attention must be paid to the 
tint : wliite, reflecting too much light, would solarize ujoon the 
proof before the face had time to come out, and, owing to its 
reflecting all the rays, a blur or irradiation woidd apjjear on all 
edges, due to cliromatic aberration. 

" It will readily be imdei'stood, that if it be desrred to intro- 
duce a vase, an imi, or other ornament, it must not be aiTanged 
against the back-ground, but brought forward imtil it appears 
perfectly distract upon the obscured glass of the camera. 

" Different paii-s of the dress, for the same reason, require 
intervals, differing considerably, to be faii'ly copied ; the white 
parts of a costume passing on to solarization before the yellow 
or black tints have made any decisive representation. We 
have, therefore, to make use of temporary expedients. A person 
dressed in a black coat and open waistcoat of the same colour, 
must put on a temporary front of a drab or flesh colom% or, by 
the time that his face and the fine shadows of his woollen clothing 
are evolved, his shirt will be solarized, and be blue, or even 
black, with a white halo around it. Where, however, the 
white parts of the dress do not expose much surface, or expose 
it obliquely, these precautions are not essential ; the white 
collar will scarcely solarize until the face is passing into the 
same condition. 

" Precautions of the same kind are necessary in ladies' dresses, 
which should not be of tints contrasting strongly. 

"■ It will now be readily understood, that the whole art of 
taking daguerreotype miniatures consists in directing an almost 
horizontal beam of light, throvigh a blue-coloui-ed medium, 
upon the face of the sitter, who is retained in an unconstraiaed 
posture by an appropriate but simple mechanism, at such a 
distance from the back- ground, or so arranged with respect to 
the camera, that his shadow shall not be copied as a part of 
his body." 

Professor Draper used a camera having for its objective two 
double convex lenses, the united focus of which for parallel rays 
was only eight inches ; they were four inches in diameter in 
the clear, and were mounted in a barrel, in front of which the 
aperture was narrowed down to tliree and a half inches, after the 
manner of Daguerre's. He also adopted the principle of bringing 


the plate forward out of the best visible fociis, into the focxis 
of the violet rays, as was first suggested by Mr. Towson, of 
Devonpoi-t, who also made many experiments, about the same 
period, with camei-as having mirrors instead of lenses. A patent 
was taken out by Mr. Woolcott, a philosophical instniment-maker 
of New York, for a camera for portraiture, with an elliptical 
mirror; which form of apparatus was also patented by Mr. Beard, 
in England, who having somewhat modified Dr. Draper's arrange- 
ments, succeeded still better in obtaining copies of " the human 
face divine." 

A camera obscura of this description is constructed as follows. 
Fig. 12 is a sectional view of the apparatus. At one end of a 








fu , "'" ^^^^-v-'^^-^— °^ 


box shaped as in the figure, and having an opening at D, is placed 
an elliptical mirror, A. The prepared plate B is fixed to the 
sliding frame c, by which it is adjusted to the best focus. The 
rays of light, radiating from a figui-e placed at F, will, it must be 
evident, pass through the opening at d, and fall on the muTor, 
as represented by the dotted lines, and will be thence reflected 
to the plate B. 

The miri-or has certainly the advantage of throwing a greater 
quantity of light upon the plate, but it has the great dis- 
advantage of limiting the size of the picture. With a mii-ror 
of seven iaches diameter, we only procure pictui-es which will 
be perfect over two square inches ; whereas, with a lens of three 
inches diameter and foiu-teen inches focal leng-th, pictures of a 
foot squai'e may be worked. From this it will be seen that the 
mirror is only applicable where single objects are to be copied. 

Eventually the sensibility of the siu-face of the plates was 
gi'eatly increased. Mr. Goddard appears to have been the first 
to employ bromine in combination with iodine ; and it was sub- 
sequently found by M. Claudet and others, that chloriue had an 
accelerating power, but not to the same extent as the bromine. 

These discoveries led to that amazing degree of sensitiveness 
which now enables us, in good light, to take a picture in less 
than a second of time. 



It is tliouglit that it may prove of some interest to a^ipend tlie 
following table, compiled witli much care for the British Asso- 
ciation, by the author, and printed by that body in their 
Reports for 1850, and to which now niimex'ous additions are 
made. It is believed that the dates of discovery are accurately 
giveii, the date of publication being, of com-se, in all cases, taken 
where there was the slightest doubt : — 


Nitrate of 

(photographically employed) 

with organic matter . 

with salts of lead . . . . 

Ritter . . . . 1801 
Wedgwood & Davy 1802 

Chloride of 

(photogi'aphically employed 

J. F. Herschel 
J. F. Herschel 
C. W. Scheele 

( Wedgwood 

\ Talbot . . . 
darkened, and hydi'iodic salts Fyfe, Lassaigne 

{ Herschel . 

( Ryan . 
Himt . . . 
J. B. Reade . 
Talbot . . 

Iodide of (photogi-aphically used) 

with ferrocyanate of potash 

■ with infusion of galls . 

with gallic acid (Calotype) . 

with protosulphate of iron 


• with iodide of iron (Catalyso- 


Bromide of 

Fluoride of 


Oxide of 

■ ■ with ammoni;i 

Phosphate of 

Tartrate — Urate — Oxalate — Bo- 
rate, &c. , 

Hunt . . 

Hunt . . 
Davy . . 
Fyfe . . 

Herschel . 









SiL"\T2i — continued. 

Benzoates of Hunt 

Fomiiates of Do. 

Fulminates of Do. 

. 1844 
. 1844 
. 1842 

Silver Plate. 

With vapoiu' of iodine (Daguerreo 


With bromine and iodine . 
"With chlorine and iodine 
With vapoiu- of sulphur . 
With vapour of phosphorus 

Daguerre . 

. 1839 

Goddai'd . 

. 1839 


. 1840 


. 1820 


. 1820 

Ctl.\ss Plate. 

Precipitates of silver Herschel . . . 1839 

Albxmien on Xiepcede St. Victor 1848 

Collodion Uncertain . . 1850 


/-,! 1 • , c i Rumford . . . 1798 

^^"^^""^ 1 Herschel . . . 1840 

Etherial solution of Eumfbrd . . . 1798 

Etherial solution of, with percya- 

nide of potassium . . . Hunt . . . . 1844 
Etherial solution of. ^vith protocja- 

nide of potassium . . . Do 1844 

Chromate of Do 1844 

Plate of gold and iodine vapour . Goddard ... 1 842 


Chloride of 

. . Herschel . 

. 1840 

Chloride of, in ether . . . 

. . Do. . . . 

. 1840 

Chloride of, with lime . . 

. . Do. . . . 

. 1832 

Iodide of 

. . Do. . . . 

. 1840 

Bromide of 

. . Hunt . . 

. 1844 

Percyanide of 

. . Do. . . 

. 1844 


Protoxide of Uncertain. 

Peroxide of Guibourt. 

Carbonate of Himt . . 




Mercury' — continued. 

Chromate of Hunt . 

Deutioclide of Do. 

Nitrate of Herschel 

Protonitrate of Herschel 

Cliloride of Boulky 

Bichloride of Yocrel . 



Protosulpliate of Hunt . . 

Perstdphate of | 

Ammonio-citi'ate of V Herschel . 

Tartrate of j 

Attention was tii'st called to the 

very peculiar changes produced 

in the iron salts in general, by Herschel . 
Cyanic compounds (Prussian blue, J Scheele 

&c.) \ Desmortiers 

Ferrocyanates of Fischer 

Iodide of Dr. Woods 

Oxalate of Hunt . 

Cliromate of Do. 

Several of the above combined with 

mercury Herschel . 


Chromate of (Chromatype) 

Sulphate of 

Carbonate of ... . 

Iodide of 

Copper-plate iodized . 





Permanganate of potash 
Chloride of ... . 


Oxide of (the puce-coloured) . 
Red lead and cyanide of potassium. 

Hunt . . 
Do. . . 
Do. . . 
Do. . . 

Talbot . . 

. . 1843 
. . 1844 
. . 1844 
. . 1844 
. . 1841 

Himt . . 

. . 1824 
. . 1844 

Davy . . 
Hunt . . 

. . 1802 
. . 1844 

Nitrate of 

Iodide of . : : : : : ; :}^^^^ 





Purple of cassius Uncei-tain. 

Cobalt Hunt . . 

Arsenic sulphuret of .... Sage . , 
Arsenical salts of 




Rhodiuji ...... 


Bichromate of potash 
with iodide of starch 

Chlorine and Hydrogen. 

Chlorine (tithonized) 
and ether 

Glass, manganese, reddened 
Cyanogen, solution of . . 



[. Hunt 


Mungo Ponton 
E. Becquerel . 


J Gay-LussacandThe- 
) nard . . . 1809 
Draper . . . 1842 
Cahoiu-s . . . 1810 

Faraday . . . 1823 
Pelouse & Richard- 

Hitter . 

in nitrogen Beckman 

and ammonia Vogel . 

Nitric Acid decomposed by light . Scheele 

Methyle Compounds Cahours 

( Petit 
Crystallisation of salts influenced J r<i-.„,-, 
by light ^j).J 








E-Esmous Bodies {Hdiography) 


Eesin of oil of lavender . 


Bitumens all decomposed 
All residua of essential oils . 
Flowers, colours of, expressed, 

spread upon paper . 
Yellow wax bleached 


KieiDce . . . 1814 
Niepce . . . 1814 
Niepce & Daguerre 1830 
WoUaston . . 1803 
Da^Tierre . . . 1839 


Biot . 
^ E. Becquerel 
Influence of light on electrical 

phenomena E. Becquerel 

Phosphorescent influences of solar 




In the foregoing chapters every thing has been included which 
appeared necessaiy to the complete illustration of the history of 
Photography. It may be thought by many that the manipulatoiy 
details included in this division should have been reserved for 
that which is more strictly technical. The difficulty of doing 
this without an annoying repetition, has led me to adopt what I 
consider to be the clearer coui-se. 







Previously to explaining the practice of photogi'apliy, to wliicli 
a separate division is given, it appears impoi-taut that the phy- 
sical conditions of the elements with which we have to work 
should be understood. 

The sim-beam is oiu^ pencil, and cex"tain delicate chemical 
l^reparations form our drawing-board. Every beam of light 
which flows ft'om its solar source is a bundle of rays, haAdug 
each a veiy distinct character as to coloui' and its chemical 
functions. These rays ai-e easily shown by allowing a pencil of 
sunlight to fall on one angle of a prism : it is bent out of its 
path, or refracted, and an elongated image is obtained, present- 
ing the various coloiu*s of which light appeal's to be constituted 
— i"ed, orange, yellow, green, blue, indigo, and violet. This 
coloured image is called the solar or the prismatic spectrum. 
The red ray, being the least refracted, is fovmd at the lower edge, 
ajid the violet, being the most so, at the other extremity of this 
chromatic series. Below the ordinarily \dsible red, another i"ay 
of a deeper red, distinguished as the extreme red, or crimson ray 



may be detected, by examining the whole tlirougli a cobalt blue 
glass ; and, by throwing the spectram upon a piece of yellow 





papei', another ray appeal's at the violet extremity, named by 
Sii' John Herschel the lavender ray. Yet more recently, Mr. 
Stokes has proved a most remarkable extension of the luminous 
rays. By throwing a prismatic spectrvim into a solution of qui- 
nine in diluted sulphiuic acid, or an infusion of the bark of the 
horse-chestnut tree, a set of extra spectral rays, extending far be- 
yond the violet, make their appearance, proving the existence of 
light over a space which has hitherto been thought incapable of 
producing any luminous phenomena. 

The original spectiTim of seven bands of colour was examined 
by Sir Isaac Newton, and that eminent philosopher determined 
that a given degree of refrangibihty indicated a given colour ; 
that the colour of a ray at once indicated its angle of refraction. 
Since the days of Newton, until our own time, this position had 
never been called in question ; the seven rays were regarded as 
the primary colours of white light, and the law of Newton 
received as tinith ujDon his authority. Sir David Brewster has, 
however, argued that this law will not stand the test of exami- 
nation. He imagines that the prismatic spectrum consists of 
three chromatic spectra overlapping each other, and that those 
three colours — red, yellow, and blue — can be detected in every 
part of the image. Sii' John Herschel has added two rays to 
the luminous or visible spectrum, — thus making the number 
nine instead of seven ; but these may, equally with the others, be 
but combinations of the three primaries. There is, however, 
much reason to doubt if the new extra spectral rays can be 
comprehended within these three. 

The colours of light will be rendered most femiliar by calling 
to memory the conditions of that very beautiful natural pheno- 
menon, the rainbow. The primary bow is usxxally accompanied 


by a secondary image, in whicli the oi'cler of the colours is re- 
vei'sed. From close examination of the prismatic spectrum, I 
am dLsposed to believe that -n-henever we obtain this chromatic 
division of white light, it is accompanied by a secondaiy spectnim, 
and that the real conditions of the coloiu-s are as follows : — 

The yellov.^ is the most luminous ray, and the illuminating 
power diminishes on either side of it ; on one side it blends with 
the blue, to form the green, and on the other with the red, giving 
rise to the orange ray. The blue diminishing in intensity sinks 
towards blackness, and thus produces the indigo, the extreme 
edge of which represents the limit of the ordinary spectrum at 
that end ; as the outer edge of the red forms its limits, as far as 
the human eye is concerned, on the other. Beyond the indigo 
we have the violet taj : this would appeal' to be the blending of 
the red of the supplementary specti-um with the blue of the 
ordinaiy one, the lavender mj resulting from the intercombina- 
tion of the less Iviminous I'ays with the coloui'ed sm-face upon 
which it is thrown. Then the extreme red or crimson ray '^'ill 
be seen to result from the blending of the extreme blue of the 
extraordinary with the red of the ordinary spectral image. This 
passage is still retained ; but I have eveiy reason to believe that 
it will before long requii-e some modification, the discoveiy of 
]Mr. Stokes materially altei-ing the conditions. 

Sir William Herschel, and Sii' Henry Englefield, determined 
the heating powei'S of these rays to be very varied. A thermo- 
meter was placed in each, and the following restdts obtained : — 

In the blue ray, in 3' the thermom. rose from 00° to oGi^, or 1° 

green '• 


yeUow '■'■ 


' full red " 


•' edge of red " 



'•' 58 

' 4 


'• 62 

' 6 


'•■ 72 

■ 16 


'• 731 



•• 79 

• 18 

Quite out of visible light in 2^' '• 

Sir John Herschel, by another form of experiment, has fully 
confirmed these results, and shown that the calorific, or heat- 
produciug radiations, being less refi-acted by the prism than the 
light-excitmg rays, exist a considerable distance further fr-om the 
\'isible rays than has been hitherto suspected. Light and heat 
have not, therefore, the same degi-ees of refi-angibdity ; their 
influences are not coincident, theu* maxima in the solar spectrum 
ai-e wide asunder. Melloni has shown that, by the use of 
coloured media, these agencies can be, to a considerable extent 
separated from each other. Glass stained ^\-ith oxide of copper, 
and washed on one side -with a colomdess solution of alum, 
admits the light rays most freely, but obstructs 95 per cent, of 



the heat rays. On the contrary, a sKce of obsidian or black 
mica obstructs nearly all the light radiations, but offers no im- 
pediment to the passage of heat. 

The chemical influences of the prismatic rays vary as their 
heating powers, but in the contraiy direction. 

If we place a jjiece of photogTaphic paper in such a position 
that the spectrum falls upon it, it will be found to be very 
unequally impressed by the various rays. Some very extraordi- 
naiy peculiaiities have been observed by Sir John Herschel and 
myself ; but it will be sufficient for oiu" present piu-jiose to state 
the general featm-es of the impression under ordinary condi- 
tions. For some distance below the visible red ray, the paper 
will be found uncoloured ; on the part where the red ray falls, 
a tinting of red or jAnk will be evident. The orange and yellow 
rays leave no stain, and the green in general but a faint one. In 
the place occupied by the blue ray, the first decided darkening 
is evident, which increases through the indigo and violet rays. 

Over this space the extra") 
spectral or fluorescent > 
rays become visible. ) 

and extends some distance beyond them. The shaded wood- 
engra^-ing (Fig. 14) will serve to assist the reader in compre- 


hencling the phenomena. The chemical radiations have a higher 
refrangibility than the ordinaiy luminous i^ays, and consequently 
they extend in fuE action to a considerable space beyond the 
lavender rays, where no light exists which can jjroduce excite- 
ment on the optic nerve of the hujuan eye, unless aided by some 
peculiar conditions of transparent media, or of optical an-ange- 

Whenever we thi'ow a prismatic spectrum upon any photo- 
graphic sui-face, it is always accompanied by a sufficient quantity 
of difiiised light to produce some chemical change, which shows 
itself in darkening, over the parts beyond the coloured image. 
However, there are two points where this change does not take 
place, and where the paper is preserved positively white; these 
are the points of maximum light and heat — the yellow and 
crimson rays. Here we have the evidence of the interference 
of these agencies with the chemical radiations. As we can 
separate heat and light from each other by the use of coloured 
media, so can we isolate the chemical and limiinous principles of 
the Sim's rays. By a yellow glass stained with silver we may 
cut off the agency producing chemical change so completely, that 
the most sensitive photogi'aphic material may be exjDOsed to a 
full flood of sunshine, without its undergoing any alteration in 
colour. If, however, we take a dark-blue glass, such as is usu- 
ally prepared with the oxide of cobalt, of so deep a colovu* that 
it obstiiicts a considerable quantity of Hght, and place imder it 
the same, or any photographic preparation, it will be found to 
darken as rapidly as if no glass had been interposed between it 
and the sim. 

Thus we obtain conclusive proof that it is not light, luvmwiis 
power, which produces the chemical change. That it is not 
HEAT is shown in the same manner by the protecting influence 
exerted by the maximum calorific raysj and therefore we ai-e 
driven to the hypothesis of the existence of a new agency — a 
new imponderable element — or a noble form of force which is 
broadly distinguished from these principles or forces in its effects. 
To mark this the term Actinism has been proposed, and it is 
now very generally adopted. The word signifies nothing moi-e 
than 7X11/ power, and therefore, as involving no theoiy, it is fi-ee 
from many of the objections which Avoidd apply to any other 
term adopted from preconceived ideas. 

Photogi'aphy ajipears to be a misnomer, since the pictures so 
called are not cbawn by hght. It is, however, too finuly rooted 
in the public mind to admit of the hope that any other may be 
adopted. If I might venture a suggestion, I would advocate a 
retm'n to the term introduced by Niepce, whose processes are 



described iu the historical section — Heliography, Sun-drawing, 
which most clearly expresses the fact, leaving the questioaof the 
particular agent effecting the chemical change still open for exa- 

The annexed figiire (15) shows the conditions as they are at 
present known. 

f Space of extra spectral 
\ rays. 

b Lavender 

Actinism, or chemi- "|_ 
cal radiant power, j 

Light, c 

Heat. D 








rt Extreme Bed. 

Prom A to B exhibits the Ne"wi;onian spectrum, a and b being 
the rays which belonged to modern discoveiy previously to the 
recent observation that the peculiar blue rays seen in solution 
of quinine and some minei'al oils belong to a yet higher order of 
refrangibility. The curves c, D, and e, represent the relative 
maxima of heat, light, and actinism, F being a second apparent 
maximum — indicated in the red i-ay — of the chemical powei-s. 
This may, however, be proved eventually to be a function of 
heat, since we know that calorific power will produce chemical 
change even when it is exercised as a radiant force. 

The operation of these antagonistic forces is somewhat re- 
mai'kably sho^vn over different regions of the earth. Advancing 
from our owTi lands towards the tropics, it is found that the 
difiiculties of obtaining pictures by the solar influences increase ; 
and, under the action of the glowing light of equatorial climes, 
a much longer period is required for impressing a photograph 
than is occupied in the process either in London or Paris. It 


has been stated by Dr. Di-aper, that in his progi-ess from New 
York to the Southern States he found the space protected fi'om 
chemical change by the yellow rays regularly increasing.. 

The same result is apparent in the differences between the 
spring and summer. Usually in March and April photographs 
are more readily obtained than in Jvme and July. 

It is worthy of notice, that the moi-ning sun, between the 
hours of eight and twelve, produces much better effects than 
can be obtained after the hom* of noon : this was observed at a 
veiy early period by Daguerre. For drawings by appUcatiou, 
this is but slightly, if at all, felt, but with the camera it is of 
some consequence to attend to this fact. We are not yet in a 
position to record more than the fact, — the cause of the diffe- 
rence is not detennined ; probably it may be found to exist in a 
greater absorptive action of the atmosphere, caused by the eva- 
poration of aqueous vapour from the earth. In the neighbour- 
hood of large towns it might be accounted for by the circumstance 
of the air becoming, during the day, more and more impregnated 
with coal smoke, &c., which offers very powerful interruption 
to the free passage of the chemical rays. This will, however, 
scarcely account for the same interference being found to exist 
in the open countn', some mUes from any town. Until our 
meteorological obseiwers adopt a system of registering the varia- 
tions of light and actinic power by means of some well-devised 
instniment, we cannot expect to an-ive at any very definite 
results. The subject involves some matters of the first import- 
ance in photometiy and meteorolog}', and it is to be desu-ed that 
oiu' public obseiwatories should be fiu-nished with the required 
instruments for carrying out a series of observations on the 
clii;mal and monthly changes in the relative conditions of the 
solar radiations. We have now e\ddence which proves that 
changes, almost inappreciable, in the condition of the atmo- 
spheric media, thi'ough which the solar rays traverse, ai-e capable 
of producing a most remarkable influence upon the colours of 
the specti*um and their chemical power. 

Many of the phenomena of vegetable life will be found to be 
directly dependent upon the operation of these principles ; and 
it would be important to mark any abnonnal states of gi'owth — 
such as not unfrequently occur — and to be enabled to refer them 
to peculiar solar conditions." 

^ See Researches on Liglit. 2nd Edition, by the Author. 



It is of some moment to tlie pliotograpliic artist that he is 
acquaiuted with the changes which occtu- in the several agents 
which he employs. A few of these are therefore selected. 

Section I. — Nitrate of Silver. 

1. The crystallised salt, in a pure state, should be procured. 
The commercial salt often contains nitrate of potash. The fused 
nitrate, which is sold in cylincMcal sticks, is yet more liable to 
contamination. A preparation is sometimes sold for nitrate of 
sUver, at from sixjience to ninepence the ounce less than the 
ordinary price, which may induce the luiwary to purchase it. 
This reduction of price is effected by frising with the salt of 
silver a projjortion of some other metalHc salt. The fi-aud is 
readily detected by observing if the salt becomes moist on expo- 
sm-e to the air, — the adulterated niti-ate of silver being delique- 
scent. The evils to the photographer are, want of sensibility 
upon exposm-e, and the perishability (even in the dark) of the 
finished drawing. 

As all the silver salts are jDrepai^ed from the nitrate, it is of 
consequence that its character and changes be clearly understood. 

Experiment 1. — Dry nitrate of silver, free of organic matter, 
will not blacken by sunshine ; and, when dissolved in perfectly 
pure distilled water, it may be exposed for a long time to solar 
influence without imdergoing any visible change. Add, how- 
ever, to the solution the smallest appi-eciable quantity of any 
organic matter, and it wiU almost immediately begin to blacken. 
This is so certain, that nitrate of silver is the most sensitive 
test that we have for the presence of organic matter in water. 

Exjjeriment 2. — Place a stick of charcoal in pure water con- 
taining nitrate of silver, most beautiful crystals of silver will form 
around the charcoal. We here see that carbonaceous matter 
has the power of effecting the decomposition of the silver salt. 
In the first examj^le, we have the metal precipitated as a black 


powder — oxide of silver and metallic silver ; in the last,, it is 
revived as a piu'e wliite metal, the ciystals being of exceeding 
brilliancy. Thus we leaiii that the organic matter of the j)aper 
or of the size, is necessary to deteimine the change on which 
the photogi-aphic phenomena depend. 

These salts have veiy 
remarkable colorific 

Section IL — Chloride of Siltek. 

For the formation of the chloride of silver, any of the follow- 
ing salts may be added to a solution of nitrate of silver : — 

1. Chloxide of Sodium (Common Salt). 

2. Chloride of Potasium. 

3. of Baiium. 

4. of Strontium. 

5- . of Calcium. 

6. Hydrochloride of Ammonia. [ properties. 

7. of Peroxide of iron. J 

8. Hydrochloric Acid (Spirits of Salts). 

9. Solution of Chlorine in water. 

The above salts are only necessaiy for the piu-pose of giving 
a variety of coloiu^ to the artist's productions ; either one of 
them may be used. Tliis is a point of much interest, as the 
result of iising these different materials as the base deter- 
mining the tone of the finished pictui'e, enables us to produce 
effects which are in accordance with the subject which we desire 
to represent. 

A few experiments of an easy character will be instructive, 
as pointing out the character of those changes which sensitive 
surfaces undergo. 

Experiment 3. — Pour some of the solution of common salt into 
the solution of niti-ate of silver ; immediately, a very copious 
white precipitate takes place. Pour off the supernatant liquor, 
and well wash it, by the dim light of a candle, with piu-e dis- 
tilled water ; then expose it to daylight : it will change colour 
very slowly, passing fi'om white to grey. Drop a little niti*ate 
of silver upon the white pi-ecipitate, it avlU dai'ken much more 
rapidly than before ; add a little organic matter, and the 
change occui-s still qiiieker ; and the degree of darkness 
which it eventually attains will be cousidei'ably deeper than 

In this experiment we prove that, although the white salt of 
silver changes coloiu' alone, the addition of nitrate of silver and 
organic matter considerably quickens the operation ; therefore, 


in preparing the papers, it is always necessary for tlie nitrate of 
silver to be in excess. 

Scheele, in his " Experiments on Air and Fire^'' has some ex- 
periments which are remarkably to the point. " I precipitated 
a solution of silver by sal ammoniac ; then I edulcorated and 
dried the precipitate, and exposed it on a piece of paper to the 
beams of the sun for the space of two weeks, when the siu'face 
of the white powder grew black ; after which I stirred the 
powder, and repeated the same several times. Hereuj)on I 
poured some caustic spii-it of sal ammoniac on this, in all ap- 
pearance, black powder, and set it by for digestion. This men- 
struum dissolved a quantity of luna cornua (horn silver), though 
some black powder remained undissolved. The powder having 
been washed, was for the greater part dissolved by a pure acid 
of nitre, which, by the operation, acquired volatility. This solu- 
tion I precipitated again by means of sal ammoniac into horn 
silver. Hence it follows that the blackness which the luna 
cornua acquii'es is silver by reduction.'''' 

Experiment 4. To determine the character of the change set up 
by sunshine. — A solution, No. 1, is nitric acid and oxide of silver 
dissolved in water, and a solution, No. 2, is chlorine and sodium. 
When these solutions are mixed, a white precipitate — chloride 
of silver — falls. The chlorine of the common salt seizes the 
silver, and as this is nearly insoluble, it is precipitated : the 
nitric acid combines at the same time with the soda, and this 
remains in solution. The chloride of silver being carefully 
washed, is placed in very piu-e distilled water, to which a minute 
portion of organic matter has been added, and then exposed to 
sunhine. After it has darkened, I'emove the water, and it will 
be found to contaia chlorine ; by adding some nitrate of silver, 
we shall obtain a fresh precipitate, and we may thus determine 
exactly the amount of decomposition which has taken place. 

In the process, the strong affinity existing has been broken 
up. Metallic silver, in a state of very fine division, is produced ; 
and the clilorine set free dissolves in the water, from which we 
can precipitate it again as chloride of silver, and consequently 
readily ascertain its quantity. 

It is necessary now to direct attention to the efiects of 
organic matter in accelerating the blackening process. Sii' John 
Herschel, whose researches in this branch of science are marked 
with his usual care, has given jjarticidar attention to this matter. 
As it is impossible to convey the valuable information that Sir 
John has published, more concisely than in liis own language, I 
shall take the liberty of extracting rather freely from his memoir, 
published in the Philosophical Transactions. 



" A great many experiments were made by precipitating 
organic liquids, both vegetable and animal, "witli solutions of 
lead ; as also, after adding alum, with aUcaHne solutions. Botli 
alumina and oxide of lead are well-kno^Ti to have an afiinity to 
many of these fugitive organic compounds which cannot be con- 
centrated by evaporation A^athout injiuy, — an aflinity suificient 
to cany them down in combination, when precipitated, either 
as hych'ates or as insoluble salts. Such- precipitates, when col- 
lected, were applietl, in the state of cream, on paper, and, when 
diy, were washed with the niti^ate. It was here that the fii-st 
prominently successfid re&Tilt was obtained. The precipitate 
thrown dowTi from a liquid of this description by lead, was found 
to give a far higher degi'ee of sensitiveness than any I had before 
obtained, receiving an equal depth of impression, when exposed, 
in comparison with mere nitrated paper, in less than a fifth of 
the time ; and, moreover, acquiring a beautiful ruddy broM-n 
tint, almost amomitiiig to crimson, with a peculiarly rich and 
velvety effect. Alumina, similarly precipitated from the same 
liqiud, gave no such result. Struck by this difference, which 
manifestly refeiTed itself to the precipitate, it now occiu-red to 
me to omit the organic matter (whose necessity I had never 
before thought of questioning), and to operate with an alkaline 
precipitant on a mere aqueous solution of niti-ate of lead, so as 
to produce simply a hych-ate of that metal. The result was in- 
structive. A cream of this hydrate being applied and dried, 
acquired, when washed with nitrate of .silver, a considerable in- 
crease of sensitiveness over what the niti-ate alone would have 
given, though less than in the experiment where organized 
matter was present. The rich crimson hue aLso acquired in that 
case under the influence of Hght, was not now produced. Two 
peculiarities of action were thus brought into view ; the one, 
that of the oxide of lead as a Ttwrdant (if we may use a tei-m 
borrowed from the art of dyeing), the other, that of organic 
matter as a colorific agent. 

" Paper washed with acetate of lead was impregnated with 
various insoluble salts of that metal — such as the sidphate, phos- 
phate, miuiate, hycModate, borate, oxalate — and others, by wash- 
ing with their appropriate neutral salts, and, when chy, applying 
the nitrate of silver as usual. The results, however, were in no 
way striking, as regards sensitivenes.s, in any case but in that of 
the muriatic applications. In all cases where such appheations 
were used, a paper was produced infinitely moi'e sensitive than 
any I had at that time made. And I may here obseiwe, that in 
this respect the mmiate of stroutia appeared to have decided 


It -would oe tedious and useless to mention all tlie combrna- 
tions of alkaliae and earthy niimates which have been de^dsed to 
vary the effect, or increase the sensitiveness of the silver pre- 
pai-ations : the veiy considerable differences produced through the 
influence of these salts will afford peculiarly interesting results 
to any inquii'er, and furnish him with a curious collection of 
photogTaphic specimens. As a general nile, all the solutions 
should be made in the combining proportions of the material 
used. With a scale of chemical equivalents at hand, the photo- 
graphic experimentalist need not eiT, taking care that a slight 
excess of pure nitrate of silver prevails upon his paper or plate. 

These changes should be well understood, before the photo- 
gTaphic amateurs proceed to the prepai-ation of the sensitive 
papers employed for the oixlinary processes. 

Section III. — Iodide of Silver. 

If iodide of silver is precipitated by mixing together solutions 
of iodide of potassiu^m and nitrate of sUver in a concentrated 
state, a heavy yellow powder falls, which "wdll scarcely change in 
colour by an exposure of many days to svmshine. But if the 
solutions are infinitely diluted, so that on mixing they only 
become milky, and the Kght powder which occasions the opacity 
falls but slowly to the bottom of the vessel, it will be found that 
it is sensitive to the weakest solar radiations. There does not 
appear to be any chemical difi'erence between the iodides thus 
obtained ; but there are some remarkable physical pecuKarities, 
and it is believed that attention to these wiU be found eventually 
to be of the utmost importance. 

Section IV. — Bromide of Silver. 

In many of the works on chemistry, it is stated that the 
chloride is the most sensitive to light of all the salts of silver • 
and, when they ai'e exposed in a perfectly fonned and piu-e state 
to solar influence, it wUl be found that this is nearly con-ect. 
Modem discovery has, however, shown that these salts may 
exist in peculiar conditions, in which the afiinities are so 
delicately balanced as to be distiu-bed by the faintest gleam ; 
and it is singular that, as it regards the chloride, iodide, and 
bromide of silver, when in this condition, the order of sensibility 
is reversed, and the most decided action is evident on the 
bromide before the eye can detect any change in the chloride. 


The slight additional expense of the bromides is not "worthy 
eonsidei'ation, particularly as their use may be confined to 
papers for the camei*a obscura, the pictures on "which are of 
course of the negative character, and the positive photogi-aphs 
can be foimed by transfer on the chloridated papei"s of a highly 
sensitive kind. Since there has been some question as to the 
use of the iodide of silver "nrithout an infringement of patent, it 
is not a little svu-j^jrising that the bromide has not been more 
generally employed. 

It "will be foimd that the bromide and iodide are much alike 
in the singular "want of sensibility "which they sometimes exhibit 
under the circiimstances ah'eady alluded 
to, "which are not easy of exi^lanation. 

If a paper first "washed "with a solution 
of nitrate of silver has bromide of potas- 
sium applied to it in different propor- 
tions, say 20 grains, 15 gi^ains, and 
10 gi-ains each, in t"wo ch-achms of "water, 
and, when cby, be again "washed over 
■with the silver solution, it will be foxmd, 
unless, as is occasionally the case, some 
organic combination interferes, that the 16 

order of sensitiveness ^vill begin "with the 

weakest solution, the stronorest bein? the least influenced by 
light. The difierent degrees of darkness induced are faii-ly repre- 
sented in the mai'gin. (Fig. 18.) As the different bromides give 
to photogi'aphic paper varieties which much resemble those 
enumerated under the muriates, I have thought it unnecessary 
to give an account of any of them. The paper prepared "with 
the bromide of potassium is the kind I have adopted, after 
ha"v-ing tried upwards of two hundred combinations of silver 
"with the other bromides. 

To prepare a highly sensitive paper of tliis kind, select some 
sheets of veiy superior glazed post, and wash it on one side 
only "with bromide of potassium — forty gi-ains to one ounce of 
distilled water, over wliich, when cby, pass a solution of one 
hundi-ed grains of nitrate of silver in the same quantity of water. 
The paper must be cbied as quickly as possible without exposing 
it to too much heat ; then again washed "with the silver solution, 
and, when dry, carefully preserved for use. 

It "n"ill be perceived that I adopt a slightly difierent manipu- 
lation fi-om that recommended by Mr. Talbot. Instead of wash- 
ing the paper with the solution of silver first, and applying the 
bromide or the mmiate over tliis, and then the silver wash ag;iin, 
I use the alkaline salt fii-st, and apply the metallic washes one 


on tlie otlier. I liave been induced to this from obsei'ving that 
the photographic prepariition penetrates less deeply into the 
paper than when laid on as originally prescribed, and, con- 
sequently, the seiLsibility of it is increased. It will be found 
that an addition of about one-twelfth of spirits of wine to the 
solution of sUver will much increase the blackness of the paper 
when solarised ; and I think we may safely say that the sensi- 
bility is also improved by it, — at all events it is not impaii'ed. 

M. Biot has expressed his opinion that it is not possible tr» 
find any substance more sensitive to Light than the bromide of 
silver : this is tme to a ceriain extent, but in combination \vith 
deoxidizing agents other prepai-ations will be named which have 
a decided superiority over the pm-e bromide of silver. 

Section V. — IMiscellaxeous Salts of Silver 

Fluoride of Silver.— The use of this salt appears to have been 
first suggested by Sir John Hei-schel ; it forms the basis of a 
process by the author, aheady described. It has lately been 
claimed as a new photogi-aphic agent by the French, but the 
date of publication determines this question in the author's 

Phosphate of Silver. — Dr. Fyfe appeai-s to have been the 
fii'st to suggest the use of the phosphate of silver as a photo- 
graj)hic material, but I am obliged to confess it has not, in my 
hands, proved anytliing like so successful as, from Dr Fyfe's 
description, it was in his own. Indeed, he himself observes, in 
speaking of its use in the camera obscura : — " Though repre- 
sentations may be got in this way, yet, so far as I have found, 
they have not the minute distinctness of those got by the method 
afready mentioned (i. e. by application). Owing to the inter- 
ference of the lens, the Light does not act neai'ly so powerfully 
on the paper, as when it has to permeate merely a frame of 

For all practical piu'poses, the method which Dr. Fyfe has 
given of prepai'ing these papers is, perhaps, the best : — " The 
paper is first soaked in the phosphate of soda, and then ch-ied, 
after which the nitrate is spread over one side by a brush ; the 
paper again di-ied, and afterwards again put tlu'ough the salt, by 
which any excess of silver is converted to phosjihate. As thus 
prepared, it acquires a yellow tinge, which becomes black by 
exposure to light." It will be evident from these dii'ections, 
that what was formerly said about the necessity of ha\TLng the 
nitrate of sUver in excess, is here, according to Dr. Fyfe, 


oLjectionahle. It certainly does not appear to be so essential 
in tliis preparation, that anything but piu-e phosphate of silver 
should be vised ; yet I cannot help fancying that a slight advan- 
tage is gained, even here, by allowing a little excess of nitrate. 
Dr. Fjfe has given a process for applying the phosphate of 
silver, mixed as a paint, on metal, glass, or paper. It, however, 
reqnii'es the skill of an artist to produce an even siu-face, and 
unless a uniform gi-ound is given, the .pictiu-e is defoiTned by 
waving lines of different shades. A method of jirecipitating 
argentine salts on smooth surfaces will be given in the following 
pages, by which means the most unifoiTa face is procured, and 
many beautiful effects produced. 

Fulminate of Silver. — Notwithstanding the extraordinaiy 
degi'ee of sensibility which has been given to paper and to 
the metallic plates by the industrious experiments of chemists, 
I am convinced that we may hope to obtain agents of far 
higher natiu-al sensibility than those we now possess ; and I 
look with much anxiety to some of the combinations of organic 
radicals with metallic bases. The fidminates and the ethyle 
compounds present a veiy promising line of inquiiy. Mr. John 
Towson, of Devonport, who piu-sued, conjointly with myself, 
a most extensive series of researches on photogi-aphic agents, 
was endeavoming to foiTQ a solution of silver, in which the 
elements shoidd be so delicately balanced as to be overturned 
by the action of the faintest light. To do this, he dissolved 
some very pure silver in nitric acid, to which spirits of wine 
was added somewhat suddenly in proportions equal to the 
acid used, and the precipitation of the fidminate prevented 
by a quick effusion of cold water, siifficient to bring the specific 
gi'avity of the solution to 1-17, and to this a few cb-ops of am- 
monia were added. Pieces of Bank post paper dipped in this 
solution became, the instant they were presented to the declin- 
ing Hght of an autumnal evening, a beautifid black having a 
pm'ple tinge. This effect did not seem to come on gradually, 
but, as by a sudden impulse, at once. Both this gentleman and 
myself have often endeavoured to rejieat this, but in no one 
instance have either of us succeeded in producing ami;hing 
neai'ly so sensitive. It shoidd be stated, that the solution pre- 
pared in the evening had become, by the foUo'w'ing morning, 
only ordinai-ily sensitive, and that papers prepared with it were 
deliquescent and bad. In repeating any modification of this 
experiment, the gi-eatest care shoidd be taken, as explosions of 
considerable violence ai-e othei'wise likely to occur. 

Another series of expeiiments on the fulminates of silver have 
produced veiy pleasing photographic residts, but I am not 


enabled to specify any particular method of preparing them, 
whicli may be certain of reproducing the results to which I allude. 
Nothing can be more capricious than they ai'e ; the same salt 
darkening rapidly to-day, which ^vill to-morrow appear to be 
absolutely insensible to radiation, and which wiW again, in a few 
days, recover its sensitiveness, to lose it as speedily as before. 

The beautiftd researches of Professor Frank land, of Owen's 
College, Manchester, however, most satisfiictorily prove that a 
great many of the metals will combine with organic radicals in 
the sunshine which will not so eomliiue in darkness. 

Organic and other Salts of Silver. — AVith the exception of 
the cai'bonate, tartrate, acetate, citi-ate, oxalate, and one or two 
others, the salts of sUver, besides those already described, do not 
appear to be sensibly influenced by Kght. Many have been 
mentioned by authors as absolutely insensible to its influence ; 
but recent expeiiments have produced modifications of these 
salts, which are delicately sensitive to the solar ray. Amongst 
othei-s, the chi'omate has been named, and certaiuly it has not yet 
been rendered sensitive to an exposiu-e of some hom-s to dayhght ; 
but one experiment of mine has proved that the solar beam will, 
in a few days, produce a fine revival of metallic silver fi.-om its 
chromate ; and another expeiiment ^vith it, has the most pleasiag 
result of biingiag ■K\'ithkL the range of probabilities, the j^iroduction 
of photogi-aphic pictiu-es yd. their natiu-al colours. 

Reseai'ches having this object in view led to the discoveiy of 
the chromatype ; but this beautiful salt (chromate of silver) has 
not yet been applied directly as the photographic agent. In 
the present state of oiu- knowledge, we cannot ventui'e to affirm 
that any salt of silver, or, indeed, of any of the other metals, 
exists, having an absolute insensibility to light, or in which the 
requii'ed unstable equilibriimi may not be induced, so that the 
Sim's beam might change the character of its combinations. I 
am, indeed, con-sinced that no body in natm-e is entii-ely unin- 
fluenced by the action of the sun's rays. Pajjei-s washed with 
either of the alkaline carbonates, and then "nn-th a solution of 
nitrate of silver, resemble in theii* character those prepai'ed with 
the miuiates, but are not darkened so readily. 

The tartrate of sil%-er possesses some very extraordinaiy pecu- 
liaiities. Papers may be prepared, either by spreading the tar- 
ti-ate at once over the surface, or better, by soaking the ^mper 
in a solution of Rochelle salt (the tartrate of potash and soda), 
and then applying two washes of the solution of niti-ate of silver. 
The fia-st action of Hght is very feeble, but there gradually comes 
on a stronger discoloiu-ation, which eventually proceeds with 
rapidity, and at length blackens to an extent beyond almost 

ORGA^^c co5ipot::nt>s with silver. 123 

every other paper. This discoloiu-ation may be Tvonderfiilly 
accelerated by washing over the tartrated paper with a veiy 
dilute solution of the hydiiodate of potash, diu-ing the process 
of darkening. It is not easy to use this when copying anything, 
but there are cases in which the extreme degi'ee of dai'kness 
which this prepai-ation acquii'es, rendei's it valuable. The acetate 
of silver comports itself in the same manner as the tartrate. 
The citi'ate, oxalate, &c., are only interesting as forming part 
of the series of argentine preparations which exhibit decisive 
changes when exposed to light. The methods of rendering them 
available will be sufficiently undei-stood from the foregoing 
details, and it would only be an imnecessary waste of words to 
give any more particiUar dii-ections as it regai"ds them. 



Numerous speculations having been ventm-ed as to the pecu- 
liar chemical changes which light produces on the iodidated 
silver tablets, I shall make no apology for introducing a few 
remarks on this very interesting subject. 

Numerous exj^eriments on plated coj)per, pure silver plates, 
and on silvered glass and paper, have convinced me that tlie fii'st 
operations of polishing with nitric acid, &c., are essential to the 
production of the most sensitive surface. All who will take the 
ti'ouble to examine the subject "will soon be con\'inced that the 
acid softens the silver, bringing it to a state in which it is ex- 
tremely susceptible of being either oxidized or iodized, according 
as the cu'cumstance may occur, of its exposure to the atmosphere 
or to iodine. The process, adopted, I believe, first in America, 
of producing a deposit of chemically pure silver on the plated 
metal, by means of the voltaic batteiy, wliich certainly gives 
rise to some peculiar conditions, appears to prove that the soft 
surface of silver is of advantage. 

The sensitive siu-face is a combination of iodine, or of iodine 
and bromine, with the silver. When exposed to radiant in- 
fluences in the camera, a molecular change is efiected, and there 
is much doubt if any iodine or bromine is removed from the 
surface. Some have thought that tlie superficial film being 
decomposed, the iodine and bromine attack a lower s\u"face of 
the plate ; but experiments are still wanting. 

I have discovered that all the rays of the prismatic spectrum 
act on the Daguerreot\'pe plate, except the yellow, and a circle 
of Kght of a peculiar and mysterious character, which surrounds 
the visible spectrum. The light acting on a prepared tablet, 
appeal's to decompose the film of iodide of silver to difierent 
depths, according to the order of refit'angibility of the rays : the 
violet ray and extra-spectral rays efiecting the . deepest decom- 
position, whilst the red acts to a depth inappreciably slight. 
Thus it is that the spectrum impressed on a Daguerreotype 
plate reflects natiu'al tints of the same kind as Sir* Isaac 
Newton's thin films ; the thickness of each film of reduced silver 

.* A 


on the plate being in exact proportion to tlie chemical agency of 
the coloiu-ed ray by "which it was decomposed. 

On photogTajjhic papei-s, the decomposed ai-gentine salt exists, 
in all probability, in a state of oxide, mixed with revived silver ; 
but on the silver tablet the iodide is changed over all the parts 
on which the light acts, and pure silver in a state of extreme 
division results. The depth to which the decomposition has 
been effected being in exact relation to the intensity and colour 
of the light radiated from the object which we desu-e to copy, the 
merciu'ial vapoiu- iinites with diiferent ijroportions of silver, aids 
in encreasing the decomposition of the silver salt, and thus are 
formed the lights and middle tints of the picture. The shadows 
ai'e produced by the unchanged silver fi-oni which the iodine is 
removed by the hyposulphite of soda. 

Daguerre himself laid much stress uj^on the necessity of ex- 
posing the plate to receive the vapoiu- of merciuy at an angle of 
4-5''. This, perhaps, is the most convenient position, as it enables 
the oi^ei-ator to view the plate distinctly, and watch the develop- 
ment of the design : but beyond this, I am satisfied there exists 
no real necessity for the angular position. Both horizontally 
and vertically, I have often produced equally efiective daguerreo- 
types. Looking at a daguerreotype pictiire in such a position 
that the light is incident and reflected at a large angle, the 
th-awing appears of the negative character ; the silver in such a 
• position appearing white, and the amalgam of mercvuy and silver 
a pale grey. Yiew the plate in an}- position which admits of 
but a small angle of reflection, and we then see the design in 
all its exquisite beauty, correct in the ai-rangement of its lights 
and shades, — the silver appearing black, while the amalgam, by 
contrast- in part, and partly in reality, appeal's nearly white. 

The cause leading to the unifomi deposition of the mercurial 
vapour is diSicult of solution. It does not appear to me that 
any one of the hypotheses put forth, satisfies all the conditions 
of this peculiar phenomenon. 

Few papers have been published which so completely investi- 
gate the phenomena of the chemical change in the daguen-eotype, 
as that of Mr. George Shaw. As giving a lai-ge amoimt of 
valuable information, I transfer it fi-om the Philosophical 

" It is well kno%vn that the impression produced by light on 
a plate of silver rendered sensitive by M. Daguen-e's process, is 
wholly destroyed by a momentary exposure of the plate to the 
vapour of either iodiQe or bromine. Although this fact has 
long been known, the natm-e of the action by which so extra- 
ordinary an efiect is produced has not yet been satisfactoiily 


explained. In tlie hope of elucidating this subject, a series of 
experiments was instituted, the results of wliich are recorded in 
the following remarks. 

" A silver plate prepared by exposure to iodine or its com- 
pounds with bromine, may be exposed to the vapour of merciuy 
without being in any way affected by the exposure. If, howevei', 
the prepared plate be previously exposed to light, or made to 
receive the luminous image formed in the camera ohscura, the 
merciu-ial vapour attacks it ; forming, in the former case, a white 
film, and in the latter, a pictm-e corresponding to the kiminous 
imasre which had been allowed to fall on it. 

" If a prepared plate, after receiving a vertical impression by 
light, be exposed to the vapoiu' of iodine or bromine, it is found 
that the vapom- of mercuiy no longer attacks it ; or, in other 
words, the impression produced by light is destroyed. 

" The first experiments made for the pm'pose of arriving at 
the cause of this phenomenon had reference to the relation 
between the time of the exposure to light and the time of ex- 
posvu-e to the vapour of iodine or bromine necessaiy to destroy 
the effect produced by light. Prepared plates were exposed in 
the camera ohscura for a length of time, which previous experi- 
ment had determined to be sufficient for a full development of 
the pictiu-e ; some of those plates were exposed dui-ing two 
seconds to an atmosphere feebly charged with the vapour of 
bromine, while others were carefully preserved from contact with 
the vapoiu"s of iodine or bromine. The atmosphere of bromine 
employed, was pi'oduced by adding thu'ty drops of a satiu-ated 
solution of bi'omine in water to an ounce of water : the solution 
was pom"ed into a glass vessel, and the plate was exposed to the 
vapoiu' in the vessel dm-ing the time specified. The plates were 
then introduced into the mercury box, and by volatilizing the 
metal, pictui'es were developed on all those which had not been 
exposed to the vapoxu' of bromine, while those which had been 
exposed to it exhibited no trace of a pictiu"e under the action of 

" The same experiments were repeated -with iodine, with 
exactly similar results. 

" Prepared plates were exposed to diffused light in the shade, 
and others were exposed to the direct rays of the sun ; the object 
being in both cases the production of a more intense impression 
than that prodviced by the feeble light of the camera ohscura. 
Some of these plates were exposed to the vapour of bromine, 
and others to the vapoiu" of iodine, while others were carefully 
preserved from the vapours of these substances. On subsequent 
exposiu-e to the vapoiu' of merciuy, those plates which had not 


beeu exposed to iodine or bromine, exhibited, by the large quan- 
tity of merciuy wbich condensed on tbem, the effects of expo- 
sure to intense light : v/hile those which had been subjected to 
the action of either bromine or iodine were in no way affected 
by the vapoiu- of mercvuy. Many repetitions of these experi- 
'ments demonstrated that the effect of exposure to the most 
intense light, was completely destroyed by the shortest exposui'e 
to the vapour of bromine or iodine. 

" Experiments were now instituted for the piui:)0se of ascer- 
taining in what condition the prepared plate was left, after having 
been fii-st exposed to light and aftei-wards exposed to the vapoiu' 
of bromine or iodine. In these experiments a method of treat- 
ment somewhat different from, and more convenient than that 
described, was resorted to, as in practising that method efiects 
occasionally presented themselves which interfered with the re- 
sults, and rendered it difficidt to determine with certainty, how 
far some of the appearances produced were due to the action of 
light. It is well known, that a prepared plate has a maximum 
of sensitiveness when the iodine and bi-omine are in a certain re- 
lation to each other : if there be a deficiency of bromine, the 
maximiun sensitiveness is not obtained, and, if there be an excess, 
the plate is no longer sensitive to light ; bxit when ■exposed to 
the vapoiu' of merciuy, loithout having been exposed to light, be- 
comes white all over, by the condensation of merciuy thereon ; 
that is to say, it exhibits the appearance of a plate which had 
been lyroperly prepared, and which had been exposed to light. 
From this it will be evident, that a plate properly prepared in 
the fii'st instance, and then exposed to light, may, by subsequent 
exposiue to the vapour of bromine, have the impression produced 
by light wholly destroyed ; and yet, by the accumulation of bro- 
mine, may exhibit, on exposure to merciuy, an appearance 
similar to that due to light. In other words, it is impossible 
(in the case supposed) to distinguish between an effect produced 
by light and an effect due to excess of bromine. By using 
iodine in the place of bromine, there is no risk of producing the 
appearance which accompanies excess of bromine ; but, on the 
other hand, by auginenting the quantity of iodine, the sensitive- 
ness of the plate is diminished. These difficidties were over- 
come by using a solution containing both iodine and bi'omine, 
in such proportions that the evaporation of each should take 
place in the proportion in which they produce on silver the most 
sensitive siu-face. The solution employed was made by adding 
alcoholic solution of iodine to a solution of chloi-ate of potash, 
until the latter woidd take up no more of the former ; and to 
each oimce, by measure, of this solution, ten di-ops of a saturated 


sokition of bromine in watei' were added. Tlie solution of 
chlorate of potash was made by diluting one part of a saturated 
solution of the salt with ten parts of water. The use of the 
chlorate is simply as a solvent of iodine. In the subsequent ex- 
periments, the plate was exposed to the vapour of this mixture 
of iodine and bromine with precisely the same effect as when ' 
either was used separately, and without the inconvenience, or 
uncertainty, which attended then* use. 

" A number of preliminary experiments, the detail of which 
would be xuiinterestiug, appeared to indicate, that not only is 
the effect of light on a dagiierreotype plate destroyed by iocUne 
or bromine, l)ut that the plate is restored to its original condi- 
tion ; in other words, that its sensitiveness to light is restored. 
In order to determine this point, the following experiments were 

" A prepared plate was exposed to light, and afterwards to 
the mixed vapour ; * mercurial vapour produced no effect upon 
it after a long exposure ; the plate on removal from the mercury 
box was a second time exposed to light, and again introduced 
into merciu-ial vapom\ The appearance of this plate was very 
little changed, and it was conckided that no effect, or, if any, 
very little, -was produced by the second exposiu-e to light. This 
conclusion was, however, erroneous, as the following experiments 
proved : — 

" A prepared plate was exposed to light, and afterwards to 
the mixed vapour : merciu-ial vapour was found to have no effect 
upon it ; the plate was then partly covered with a metallic 
screen, fixed close to, but not in contact with it, and the whole 
was exposed to Kght. On placing the plate in the merciuy box, 
a broad white band, nearly corresponding to the edge of the 
defended part, made its appearance ; the whole of the defended 
part (excepting the band in question) was unaffected, and the 
exposed part exhibited very little change. By a careful exami- 
nation of the plate after it was removed from the mercury box, 
the white band in the middle appeared to be produced by the 
feeble light wliich had passed imder the edge of the metal i:)late 
which had screened the light fr-om part of the prepared surface ; 
and the veiy dai-k, and apparently unaltered appearance of the 
exposed part, was occasioned by an excess of action, for mercury 
was found to have condensed on that part in large quantities, 
and to have produced the dark lead colour which is commonly 
called solarisation ; but which effect, in the case in question, 

* " I shall hereafter call the mixed vapours of iodine and bromine produced 
in the way described in the last paragraph but one, mixed vajjour, in order to 
avoid circumlocution. — G. S." 


was SO excessive, that the colour of the part on which merciiry had 
condensed differed but very slightly 6'om that on which no light 
had fallen. It was now e\'ident that the apjiarent absence of 
effect in the last experiment was in reality occasioned by an ex- 
cess of action ; and by repeating that experiment, and making 
the time of the second exposure to light much shorter than 
before, the plate assumed, under the action of mercury, an in- 
tense and beautiful whiteness. 

" From these experiments, then, it was perfectly clear that 
the impression produced by the light on a Daguen-eotype plate 
is wholly destroyed by the mixed vapom', and that its sensitive- 
ness to light is restored. 

" It now remained to discover to what extent the sensitive- 
ness is restored by the treatment in question. It was not at 
first expected that the sensitiveness to light was as great after 
tills treatment as after the original preparation of the plate ; 
but experiments aftei-wards proved that the sui"face lost none of 
its sensitiveness by this treatment, nor even by numerous repe- 
titions of it. A prepared plate was exposed to light ; the im- 
pression was destroyed and sensitiveness restored by the mixed 
vapour ; the plate was a second time exposed to light and a 
second time to bromine ; still its sensitiveness appeared unim- 
paii'ed, for a fourth or fifth exposure gave, on treatment with 
mercmial vapoui', a vivid impression. In order to determine 
with the greatest accui-acy if the sensitiveness of the prepared 
surface was at all impaired by these repeated exposures to light, 
the camera ohscura was resorted to. A series of plates was jire- 
pared with the utmost attention to uniformity ; some of these 
were exposed in the camera ohscura, and pictiu^es obtained by 
the subsequent exposure to vapour of merciuy : the time re- 
quisite for the proper development of the picture was noted ; 
others were first exposed to the direct rays of the sim, and after- 
wards to the mixed vapour, and these were exposed in the 
camera ohscura for the same length of time as those which had 
not been exposed to light. On treatment with mercurial vapour, 
perfect pictvu-es were produced, which could not be distiuguislied 
fi-'om those taken on plates prepared by the ordinary method. 
So completely does the mixed vapoiu- restore the sensitiveness 
of prepared plates after exposiu^e to light, that the most beau- 
tifid impressions were obtained in the camera ohscura in two 
seconds on plates which had previously been four times exposed 
to the direct light of the svm, and after each such exposure 
treated ^vith the mixed vapour. 

" As the ] Jates experimented on, to this stage of the inquiry, 
had been wholly exjDosed to the sun's light previous to exposure 


in tlie caviera obscura, it was tlioiight that possibly some sHglit 
effect was produced, which, from being the same on aU parts of 
the plates, escaped observation ; and in order to avoid the possi- 
bility of error from this cause, the impressions of light which it 
was intended to destroy by bromine were afterwai'ds made in the 
camera ohscura. Prepared plates were impressed ydxk vri-tual 
images of different kinds, the camera ohscura being pointed first 
at a house, afterwai-ds to a bust, next to a tree, and finally to a 
living figTu-e, the plates after each impression, excepting the last, 
beiQg momentarily exposed to the mixed vapom". In every in- 
stance, the most perfect impressions of the objects to which the 
camera ohscura was last dii-ected were obtained, and no trace of 
the previous impressions was left. 

'' Experiments were next instituted for the purjiose of ascer- 
taining if the prepared sui'face, after the process of merciuiali- 
zation, could be made to receive another impression by treatment 
with mixed vapoiu-. Impressions were taken with the camera 
ohscura, and after the full development of the picture by vapour 
of merciuy, the plates were exposed to bromine and again placed 
in the camera ohscura, the instrument being dii-ected in different 
experiments to diflerent objects : on exposui'e to merciuial 
vapoiu", other pictm-es made their appeai-ance, and althovigh con- 
fused fi'om superposition on the fii'st pictiu'es, could be clearly 
traced, and were found perfect in every part. This production 
of pictm-e upon pictiu-e was repeated, imtil, by the confrision of 
the supei-}3osed images, the effects of further exposui-e could be 
no longer distingiushed. 

"In all the experiments hitherto described, the destniction of 
the impressions by bromine was effected in the dark, the ap- 
paratus being situated in a room into which only a very feeble day- 
light was admitted. It remained to be discovered if the mixed 
vapoiu' had the power of destroying the effect of light while the 
plate was still exposed to light, or if the vapoiu- had the power 
oi susjoending or 2)reveiiti/ig the action of light on a daguerreotype 
plate. In order to determine this point, the apparatus was 
placed near the window of a well-lighted room, and so ari-anged 
that, dui'ing the whole time of the preparation of the plate, by 
exposiu'e fii'st to iodine and afterwards to bromine, it was ex- 
posed to full daylight, and by a mechanical aiTangement, of too 
obvious a natm-e to render description necessaiy, the plate was 
withdi-awn from the bromine vessel into a dai'k box ; that is to 
say, it was withch-awn at the same moment from the influence of 
both light and bromine : on being placed in the camera ohscura, 
plates so prepai-ed received impressions which by mercimaKzation 
produced excellent pictures, and there was no trace of the action 


of any Hglit save that of the carniera ohscura. It follows, then, 
that light is incapable of exerting any appreciable influence on 
daguerreotype plates during the time they are receiving their 
coatings of iodine and bromine. 

" Although these experiments afford no information on the 
subject in reference to which they were originally undertaken, 
they are yet not without interest, both in their theoretical 
bearing and in theii- practical application. They demonstrate 
not only that the change (whatever it may be) effected by light 
on silver plates prepared by DagueiTe's process, is completely 
siispended in the presence of the vapoiu- of either iodine or bro- 
mine, but that after that change has been produced the impres- 
sion may be destroyed, and the plate restored to its original 
condition, by a momentaiy exposru'e to either of these vapours. 
In their practical application, these experiments show that all 
the care which has been taken to exclude Kght from daguerreo- 
type plates diu'ing theii* pi-eparation is unnecessaiy ; that so far 
from a dark room being essential to the operations of the da- 
guerreotype artist, the Kght of day may be allowed to fall on 
the plate dui'ing the whole time of its preparation ; and that it 
is only necessaiy to -^dthdraw it at the .same moment fi'om the 
action of bromine and light by sKding it fr-om the bromine vessel 
into the dai'k box in wliich it is can-ied to the camera ohscura ; 
and where, fr-om the situation or otherwise, there is a difficulty 
in obseiwing the colour of the plate during the process of iodizing, 
it may be removed fr-om the iodine vessel, and its^colour examined 
by the direct light of the sun, without risk or injiuy : for when 
returned to the iodine or bromine vessel for a moment, the effect 
of light is wholly destroyed. 

" Perhaps the most valuable pi-actical application of these facts 
is in the use of the same plate for receiving several impressions. 
When, on taking the portrait or picture of any object liable to 
move, there is reason to suppose that the motion of the person 
or object has rendered the operation useless, it is not necessary 
to thi'ow aside the plate on which the imperfect impression has 
been taken, and resort to the tedious process of cleaning and 
prepaiing another ; it is only necessaiy to treat the plate in 
the manner already pointed out, and it is again equal in every 
respect to a newly-prepared plate ; and this treatment may be 
repeated, until, by the slow accumulation of too thick a film of 
iodide of silver, the plate no longer possesses the same degree of 
sensitiveness to Ught." 

The researches of M. Claudet are ot considerable importance, 
particularly as being those of a thoroughly practical photo- 
graphic artist. 


The plienomena which M, Claudet considers have not yet 
been satisfactorily explained, and of which he treats, are those 
referj'ing to the following points : — 

1. Which is the action of light on the sensitive coating 1 

2. How does the mei"curial vapour produce the daguerreotype 
image 1 

3. What are the particular rays of light that impai-t to the 
chemical siu-face the affinity for mercuiy ? 

4. Which is the cause of the difference in achromatic lenses 
between the visual and photogenic lenses 1 why do they con- 
stantly vary ? 

5. What are the means of measuring the photogenic rays, 
and of finding the true focus at which they produce the image 1 

At the meeting of the British Association at Swansea, M. 
Claudet expressed his opinion that the decomposition of the 
chemical sxu'face of the dagTierreotype plate, by the action of 
certain rays of light, produced on that sui-face a white precipi- 
tate, insoluble in the hyposulphite of soda, which, when examined 
by the microscope, had the appearance of crystals reflecting 
light, and which, when seen by the naked eye, were the cause of 
a positive dagTierreotype image. These were probably particles 
of pure white silver. 

The opinion of DagueiTe himself, and other writers, was, that 
the action of light on the iodide of sUver had only the effect of 
darkening the siu-face, and consequently of prodiicing a negative 
image. But it escaped them, that, under the darkened iodide 
of silver, another action could take place after a continued ex- 
posure to light, and that the hyposulphite of soda washing could 
disclose a positive image. M. Claudet proved this fact in ob- 
taining, by the action of light only, and without mercury, images 
having the same appearance as those developed under the action 
of mercurial vapour. This direct and immediate effect of light 
is certainly remarkable ; but the dagaxerreotype process is not 
founded on that priuciple, on account of the slowness of its 
action ; and it is fortunate that, long before light can produce 
the white precijntate alluded to, it operates another effect, 
which is the wonderful property of attracting the vapour of mer- 
ciuy. This vapour is condensed in the form of a white powder, 
having also, when examined by the microscope, the appearance 
of reflecting crystals. 

It is pi'obable that light exei'cises a two-fold action on the iodide 
of silver, whether it is combined or not with chlorine or bromine. 
By one, the iodide is decomposed, and the silver set free is pre- 
cipitated on the surface in the form of a white powder or small 
crystals ; by the other, which begins long before the former, 


the parts affected by light have been endowed with an affinity 
for mercm'ial vapoui-. 

By means of his photographometer, this investigator has been 
able to ascertain that the pxu-e light of the sun perforins in 
about two or three seconds the decomposition of the bromo- 
iodide of silver, which is manifested by the white precipitate ; 
while the same intensity of light determines the affinity for mer- 
ciu'ial vapour in the short space of about i Vo o^^ P^^ '^^ ^ second. 
So that the affinity for mercury is imjmrted by an intensity of 
light 3000 times less than that which produces the decomposi- 
tion manifested by the white precipitate. 

For this reason it is difficult to suppose that the two actions 
are the same. We must admit that they ai-e different. Long 
before it can effect the decomposition of the siu-face, light im- 
parts to the sensitive coating the affijoity for mercui'ial vapour ; 
and this ajjpears to be the j^i'inciple of the formation of the 
image in the daguerreotype process. 

In a paper communicated to the Royal Society on the 17th 
of June, 1847, M. Claudet stated that the red, orange, and 
yellow rays were destroying the action of white light, and that 
the siu'face was recovering its former sensitiveness or unaffected 
state after having been submitted to the action of these rays. 
It was inferred fi-om that ciu-ious fact that light coidd not have 
decomposed the surface ; for if it had, it wovdd be difficult to 
imderstand how the red, oi-ange, or yellow rays could combine 
again, one with another, elements so volatile as bromine and 
iodine, after they had been once separated from the silver. 
These experiments have much in common ^vith those of M. 
Edmond Becquerel, who has been led to a division of the spec- 
trum into exciting rays and continiiating rays. But he had not 
yet been able to ascertain that, when light has decomposed the 
bromo-iodide of silver, the red, orange, or yellow rays cannot 
restore the siu'face to its former state. The action of light, 
which can be destroyed by the red, orange, or yellow rays, does 
not determine the decomposition, which woidd requii'e an inten- 
sity 3000 times greater ; it is the kind of action produced by an 
intensity 3000 times less, giving the affinity for mercmy, which 
is completely destroyed by the i-ed, orange", or yellow rays. 
White light, or the chemical rays which accompany it, communi- 
cate to the surface the affinity for mercmy ; and the red, orange, 
or yellow rays withdi~aw it. This is in effect the same pheno- 
menon as Dr. WoUaston observed with the tinctiu'e of giun 
guaiacum ; one set of rays restoring the colour which another 
set had removed. A singular anomaly requires notice : viz. that 
when the sensitive svu'face is prepared only with iodine without 


bromine, the red, orange, or yello-w rays, instead of destroying 
the action of white light, continue the effect of decomposition 
as well as that of affinity for merciuy. Still there is a double 
compound of iodine which is far more sensitive than the simple 
compound, and on which the red, orange, or yellow rays exercise 
their destiiictive action as in the case of the bromo-iodide. 

The phenomenon of the continuing action of the red, orange, 
or yellow rays, on the simple compound of iodide of silver, was 
discovered by M. Ed. Becquerel ; and soon after M, Gaudin 
found, that not only those rays continue the action by which 
mercmy is deposited, but that they develope without mercury 
an image having the same appearance as that produced by mer- 
cm'ial vapoiu'. 

M. Gaudin, not having observed the fact of the white precipi- 
tate, which is the result of the decomposition by the action of 
light, coidd not explain the cause of the image brought out under 
the influence of the yellow ray. 

M. Claudet states that the iodide of silver without bromine 
is about 100 times more sensitive than the bromo-iodide to the 
action of the rays which produce the decomposition of the com- 
pound foiming the white precipitate of silver, while it is 100 
times less sensitive for the effect which gives the affinity for 
mercury. It may be that, in the case of the iodide of silver 
alone, the decomposition being more rapid, and the affinity for 
merciuy slower than when bromine is added to the comjiound, 
the red, orange, or yellow rays having to act upon an incipient 
decomposition, have the power, by theii' o^vn photogenic influ- 
ence, of continuing the decomposition when it has begvm. This 
may explaiu the development of the image under red, orange, or 
yellow glasses, according to M. Gaudin's discovery. But in the 
case of the bromo-iodide of silver, the red, orange, or yellow rays 
have to exert their action on the affinity for mercury, begun a 
long time before the decomposition of the compound ; and they 
have the property of destroying that affinity. 

So that it would appear that all the rays of light have the pro- 
perty of decomposing the iodide of silver in a longer or shorter 
time, as they have that of producing the affinity for mercury on 
the bromo-iodide of silver : with the difference, that, on the 
former comjDound, the separate actions of the several rays con- 
tinue each other, and that on the second compoimd these separate 
actions destroy each other. We can understand that, in the fii-st 
case, all the rays are capable of operating the same decomposi- 
tion ; and that in the second, the affinity for mercuiy when im- 
parted by one ray is destroyed by another. This would explain 
the various phenomena of the formation of the two different de- 


posits, and also the anomaly of the continuation of the action by 
the red, orange, or yellow rays, according to M. Ed. Becquerel's 
discovei'ies on the iodide of silver ; and of the destruction of that 
action by the same rays, according to M. Claudet's observations 
on the bromo-iodide of silver. 

The red, orange, and yellow rays, when acting on an unaffected 
sixrface, are considei'ably less capable than the most refrangible 
rays, of imparting the affinity for mercurial vapour on both the 
iodide and bromo-iodide of silver ; and they destroy that affinity 
when it has been produced on the bromo-iodide of silver by the 
photogenic rays. It follows from this fact, that when the red, 
orange, or yellow rays are more abundant in the light than the 
most refrangible rays, the photogenic effect is retarded in pro- 
portion to the excess of these antagonistic rays. This happens 
when there exist in the atmosphere some vaporirs which absorb 
the most refrangible I'ays. In these circumstances the light ap- 
pears rather yellow ; but it is very difficult to judge by the eye 
of the exact colour of the light, and of the propoi'tion of photo- 
genic rays existing in the atmosphere at any given moment. 

The vapours of the atmosphere which I'ender the light yellow, 
act as any other medium intercepting the blue rays, and those 
which have the same degree of refrangibility. 

If we cover an engraving one-half with light yellow glass, and 
place it before a camera obscura, in order to represent the whole 
on a daguerreotype plate, we shall find that during the time 
which has been necessaxy to obtain the image of the half not 
covered, not the slightest effect has been produced on the half 
covered with the yellow glass. 

Now, if we cover one-half with deep blue glass, and the other 
with the same light yellow glass, the engi-aving will be seen very 
distinctly through the yellow glass, and not at aU through the 
blue. In I'epresenting the whole, as before, on the daguerreotype 
plate, the half which was clearly seen by the eye has produced 
no effect ; and in the other, which could not be seen, is as frdly 
i-epresented, and in nearly as shoii; a time, as when no blue glass 
had been interposed. 

Thus we might construct a room lighted only throiigh an inclo- 
sure of pale yellow glass, in which light woidd be very dazzling 
to the eye, and in this room no photographic operation coidd be 
performed ;* or in a room inclosed by deep blue glass, which 
would appear very dark, and in which the photographic opera- 
tion would be nearly as rapid as it would be in open air. 

* I have recently proved that this statement requires some modification ; the 
rays permeating many yellow glasses act powerfully on the sensitive surfaces 
of collodion and iodine. 


Thus we may conceive certain states of the atmospliere under 
which thei'e will be an abundance of illuminating rays, and very 
few actinic rays ; and some others, under which the I'everse will 
take place. Considering how difficult it is to judge by the eye 
alone of the chemical state of light, we can understand why the 
photographer is constantly deceived in the effect he tries to pro- 
duce, having no means to ascertain beforehand, with any degree 
of certainty, the intensity of light. For these reasons M. Clau- 
det tiu-ned his attention to contrive an apparatus by which he 
could test at the same time the sensitiveness of the daguerreo- 
type plate and the intensity of light. This instrument he called 
a Photographometer. 

" By this instiniment," says the inventor, " I have been able to 
discover at what degree of intensity of light the effect called 
solarization is produced : on well-prepared plates of bromo-iodide 
it does not begm under an intensity 512 times greater than that 
which determines the first effect of mercury ; and also at what 
degree the decomposition producing the white precipitate without 
mercury manifests itself, both on iodide and on bromo-iodide of 
silver. On the first, it is 100 times quicker than on the bromo- 
iodide : and on the last it is produced by an intensity 3000 times 
greater than that which developes the first affinity for^ mercury. 

" In the course of my experiments I noticed a ciu-ious fact, 
which proved very puzzling to me, until I succeeded in assigning 
a cause to it. I shall mention it here, because it may lead to 
some further discoveries. I observed that sometimes the spaces 
under the round holes, which had not been affected by light 
dm-ing the operation of the photogi-aphometer in a sufficient 
degree to determine the deposit of merciuy, were, as was to be 
expected, quite black ; while the sj^aces suiTounding them were 
in an unaccountable manner slightly affected by mercury. At 
first I could not explain the phenomenon, except by siqjposing 
that the whole plate had been previously by accident slightly 
affected by light, and that the exposure through the holes to 
another sort of light had destroyed the former effect. I was 
naturally led to that explanation, having before observed that 
one kind of hght destroys the effect of another; as, for example, 
that the effect of the light from the north is destroyed by the 
light ft'om the south, when certain vapoui's existing in the latter 
portion of the atmosphere impart a yellow tint to the light of 
the sun. But after repeated experiments, taking great care to 
protect the jjlate from the least exposui-e to light, and recol- 
lecting some experiments of M. Moser (see Chapter on Ther- 
mography), I fomid that the affinity for mercury had been im- 
parted to the su.rface of the Daguerreotype plate by the contact 


of the metallic plate having the roimd holes, while the space 
under the hole had received no similar action. But it must be 
observed that this phenomenon does not take place every time ; 
some days it is frequent, and in some others it does not manifest 
itself at all. Considering that the plate fiu-nished with roimd 
holes is of copper, and that the Daguerreotype plate is of silver 
plated on copper, it is probable that the deposit of mercmy is 
due to an electric or galvanic action deterjained by the contact 
of the two metals ; and perhaps the circumstance that the action 
does not take place every time, will lead to the supposition that 
it is developed by some peculiar electric state of the ambient 
atmosphere ; and by a degree of dampness ia the air which 
would increase the electric ciuTent. JMay we not hope that the 
conditions being known in which the action is produced, and by 
availing ourselves of that property, it ^\all be possible to increase 
on the dag-uerreotype plate the action of light ? for it is not 
improbable that the affinity for mercury imparted to the plate 
is also due to some electrical influence of light. How could we 
othei"wise explain that affinity for mercury given by some rays 
and withdi'a"svTi by some others, long before light has acted as a 
chemical agent 1 

" The question of the actiaic focus is involved in another kind 
of mystery, which requires some attention. I have found that 
with the same lenses there exists a constant valuation in the 
distance between the two foci. They are never in the same 
relation to each other : they are sometimes more or less sepa- 
rate ; in some lights they are very distant, and in some others 
they are veiy near, and even coincide. For this reason I con- 
stantly try their position before I operate. I have not been able 
to discover the cause of that singular phenomenon, but I can 
state positively that it exists. At first, I thought that some 
variations in the density or dispersive power of the atmosphere, 
might produce the alteration in the distance between the two 
foci; or that when the yellow ray^ were more or less abundant, 
the visual rays were refracted on diffisrent points on the axis of 
the foci, according to the mean refrangibHity of the rays com- 
posing white light at the moment. But a new experiment has 
proved to me that these coidd not be the real causes of the 
variation. I generally employ two object-glasses; one of shorter 
focus for small pictures, and the other of longer focus for larger 
images. In both, the actinic focus is longer than the visual 
focus ; but when they are much separated in one they are less 
so in the other : sometimes, when they coincide in one, they are 
very far apart in the other, and sometimes they both coincide. 
This I have tried every day during the last twelve months, and 


I have always found the same variations. The density of the 
atmosphere, or the colour of Hght, seems to have nothing to do 
with the phenomenon, otherwise the same caiise would produce 
the same effect in both lenses. I must obsei've, that my daily 
experiments on my two object-glasses are made at the same 
moment and at the same distance for each, other^vise any 
alteration in the focal distance would disperse, more or less, 
the actinic rays, whiaii is the case, as it is easy to prove. The 
lengthening or shortening the focus, according to the distance 
of the object to be represented, has, for effect to modify the 
achromatism of the lenses. An optician, according to M. Lere- 
bours' calculation, can at will, in the combination of the two 
glasses composing an achromatic lens, adapt such curvatures 
or angles in both that the visual focus shall coincide with 
the actinic focus ; but he can obtain this result only for one 
length of focus. The moment the distance is altered, the two 
foci separate, because the visual and actinic rays must be re- 
fracted at different angles in coming out of the lens, in order 
to meet at the focus given for one distance of the object. If 
the distance is altered, the focus becomes longer or shorter ; 
and as the angle at which different rays are refracted remains 
nearly the same, they cannot meet at the new foctis, and they 
fonn two images. If the visual and actinic rays were re- 
fracted parallel to each other, in coming out of the lens they 
would always coincide for every focus ; but this is not the case. 
It seems, therefore, impossible that lenses can be constructed in 
which the two foci will agree for all the various distances, until 
we have discovered two kinds of glasses in which the densities 
or the refractive jiower wiU be in the same ratio as the dispersive 



Section I. — Photographic Registration. 

There are so many advantages attendant on self-registration, as 
to make the perfection of it a matter of much interest to eveiy 
scientific enqiiii'er. Tlie fii-st wlio suggested tlie use of photo- 
graphic paper for this purpose was Mr. T. B. Jordan, who 
brought the subject before a committee of the Royal Cornwall 
Polytechnic Society, on the 18th of Febx'uary, 1839, and exhi- 
bited some photographic registers on the 21st of March of the 
same year. The plan this gentleman adopted was to fiimish 
each instrument with one or two cylinders containing scrolls of 
photographic paper. These cylinders are made to revolve slowly 
by a very simple connection with a clock, so as to give the paper 
a progressive movement behind the index of the instiiiment, 
the place of which is registered by the representation of its own 

The application of this principle to the barometer or thermo- 
meter is most simple ; the scale of either of these instiiiments 
being perforated, the paper is made to revolve as close as possible 
to the glass, in order to obtain a well-defined image. The 
cj'Hnder being made to revolve on its axis once in forfy-eight 
hovu's, the paper is divided into forty-eight parts by vertical lines, 
which are figiu*ed in correspondence with the hoiu" at which they 
respectively arrive at the tubes of the instiimients. The 
graduations on the paper con^espond to those on the dial of the 
barometer or scale of the thermometer, and may be printed on 
the i^aper fi-om a copperplate, or, what is much better, may be 
printed by the light at the same time from opaque lines on the 
tube, which would of course leave a light impression on the 
paper : by this means we shoidd have all that part of the paper 
above the mercury darkened, which would at the same time be 
gi-aduated with white lines, distinctly marking the flvictuations 
in its height for every minute diu'ing daylight, and noting the 
time of eveiy passing cloud. 


Mr. Jordan lias also published an account of his veiy inge- 
nious plan of applying the same kind of paper to the magne- 
tometer or diiirnal variation needle,* and several other philo- 
sophical instriunents ; but as these applications were not at the 
time eutii-ely siiccessful, owing principallj^ to the difficulty of 
finding a suitable situation for so delicate an instiiiment, it is 
thought unnecessary to occupy these pages with any particular 
description of the aiTaugements adopted, which, however, were 
in all essential points similar to those employed by Mr. Ronalds, 
and adopted in some of om- magiietic and meteorological obser- 
vatories. Those of Mr. Brooks are of somewhat more refined a 
character, and require special notice. 

A reflector is attached to the end of a delicately suspended 
magnet ; this reflects a pencil of strong artificial light upon 
photographic paper placed between two cylindei-s of glass, which 
are kept in motion by a small clock arrangement. As the paper 
moves in a vertical direction whilst the magnet oscillates ia a 
horizontal one, a zigzag line is mai'ked on the paper ; the extent 
of movement on either side of a fixed line showing the deviation 
of the magnet for eveiy horn- of the day. By means of this 
arrangement many most remarkable phenomena connected with 
terrestrial magnetism have been discovered, and since the methods 
of adjustment have been rendered more perfect, and the inven- 
tion applied to a gi'eat variety of instruments, we may hope for 
yet more important results. 

The registration of the ever-varying intensity of the light is 
so important a subject, that it has occiapied the attention of 
several eminent scientific observers. Su' John Herschel and 
Dr. Daubeny have applied their talents to the inquiry, and 
devised insti-uments of much ingenuity for the purpose. The 
instrument constructed by Su' John Herschel, which he has 
named an actinograph, not only registers the direct efiect of 
solar chemical radiation, bvit also the amoimt of general actinic 
power in the visible hemisphere ; one portion of the apparatus 
being so arranged that a sheet of sensitive paper is slowly 
moved in such a direction, that the dii-ect rays of the sun, when 
unobscured, may fall upon it through a small slit made in an 
outer cylinder or case, while the other is screened fi.'om the 
incident beam. The paper being fixed on a disc of brass, made 
to revolve by watch-work, is afiected only by the light which 
" emanates from that definite circumpolar region of the sky to 
which it may be considered desii'able to limit the obseiwation," 
and which is admitted, as in the other case, through a fine sht in 
the cover of the instrument. 

* See the Sixth Annual Eeport of the Eoyal Cornwall Polytechnic Society. 



Mr. Jordan has devised an instrument for numerically regis- 
tering the intensity of the incident beam, which appears to 
have some peculiar advantages ; a description of which I shall 
take the Kberty of transcribing. Figau'e 17 is an elevation of 
the instrument ; it consists of two copper cylinders supported 

on a metal frame : the interior one is fixed to the axis and does 
not revolve, being merely the support of the prepared paper ; 
the exterior cylinder is made to revolve about this once in 
twenty -foiu* houi-s by a clock movement. It has a triangular 
aperture cut down its whole length, as showTi in the figui-e, and 
it carries the scale of the instrument, which is made to spring 
closely against the prej^ared paper. This scale or screen is 
composed of a sheet of metal foil between two sheets of var- 
nished paper, and is divided into one hundred pai-ts longitudinally, 
every other part being cut out, so as to admit the light to the 
prepared paper Avithout any transparent medium intervening. 
The lengths of the extreme divisions, measm'ing round the 
cylinder, are proportioned to each other as one to one hundred ; 
consequently the lower di\'ision will be one hiindi-ed times longer 
passing over its own length than the upper one over its own 
length, and the lines of prepared paper upon these divisions will, 
of coiu'se, be exposed to the light for times bearing the same 
proportion to each other. 

Now, as the sensitiveness of the paper can readily be adjusted, 
so that the most intense light vnU only just tint it through the 
ujiper division diiring its 2)(issage imder the opening, and the 
most feeble light will produce a similar tint through the lower 
division dui'ing its passage, the nmnber of lines marked on the 
paper at any given time ^\dll furnish a comparative measiu'e of 
the intensity of solar light at that time, and may be registered 
as so many degrees of the Heliogra^yh, the name Mr. Jordan 


has given liis instrument, just as "sve now register tlie degrees of 
the thermometer. 

An instrument of this kind was made by me for the British 
Association, and experiments carried on with it, at intervals, for 
some years. Many of the results were very cui-ious, but the 
instiiunent being placed at the Obsenatory at Kew, the obser- 
vations were unfoi-tunately discontinued.* It is believed that, 
with an instmment properly constiiicted, the details of the 
one employed were capable of much improvement ; many very 
remarkable altei-ations in the relative chemical power of the 
solar i-adiations would be detected. From the indications I 
have obtained, I believe there exists a constant law of change, 
and that the correct expression of the phenomena is given in 
the following pa.ssages — the concluding summary of my Report 
on this subject to the British Association at Edinburgh : — 

" It will be evident that the question which assumes the ipost 
prominence in our consideration of these remarkable phenomena 
is that of the identity or othei'wise of Kght and actinism. 

" Fresnel has stated that the chemical effects produced by the 
influence of light are owing to a mechanical action exerted by 
the molecules of fether on the atoms of bodies, so as to cause 
them to assume new states of equilibrium dependent on the 
nature and on the velocity of the vibrations to which they are 

" Arago says, it is by no means proved that the photogenic 
modifications of sensitive siu'faces result fi-om the action of solar 
light itself. These mocUfications are perhaps engendered by 
invisible radiations mixed with light properly so called, proceed- 
ing with it, and beuig similarly refi'acted. 

" These views fairly represent the condition in which the argu- 
ment stands, and a yet more extensive set of experiments seems 
to be necessaiy before we can decide the question. It appears, 
however, important that we should dismiss, as completely as 
possible, from our minds, all preconceived hypotheses. The 
phenomena were all iinknown when the theories of emission and 
of undulation were fi-amed and accepted in explanation of 
luminous effects ; and it will only retard the discovery of the 
truth, if we prosecute oiu' researches over this new gi'oimd, with 
a determination to bend all our new facts to a theory which was 
framed to explain totally dissimilar phenomena." 

* A new instrument has been constructed, and a regular series of observations 
are now in progress. 



Section II. — Instbuments for Measuring Actinic 
Variations, &c. 

the photogbaphojieter. 

M. Claiidet has devised tlie Photograpliometer and the 
Dynactinometer for measiu^iug the intensity of the actinic 
radiations. These are both most ingeidoiis instiniments, the 
operations of which will be rendered intelligible by the following 
description : — 

The accompanying figure (18) shows the photogxaphometer 

complete. The sensitive plate or paper is placed in a dai'k box, 
which is placed in an independent frame, as shown in Figs. 20 
and 21, and as placed in its position at F in the adjoining cnt. 
A black silk webbing being fixed to the moveable plate seen at 


the head of the instrument, and strained over two rollers, r, r, 
it will be evident that the sensitive plate is screened from light 



until the moveable slide falling down tlie inclined plane passes 
over it. The openings in this moveable plate are parallel to 
each other. They are seven in number, each opening being 
one-half of the following one, and double that of the preceding 
one. Thus, after the operation of the light, we have seven 
separate images, the different intensities of which represent the 


action of light during the intervals of time in the geometric 
progression of — 1 ; 2 : 4 : 8 : 16 : 32 : 64 : 

The box in which the plate or paper is placed for experiment, 

is pierced with holes, and these correspond with the slits in A B. 
(fig. 22). By inclining the instrument, which can be verj' 



readily done to any degree by means of the curved arms c D E, 
any A^elocity can be given to tlie falling screen, and thus the 
plate be exposed to the action of the chemical rays for any period 
of time we please. Fig. 20 shows the result obtained on a plate 
by this instrument ; the lettei"s corresponding with the holes iu 
the other woodcuts. In fig. 2 1 the screen with the vei-tieal slits 
is shown at the moment it is supposed to be passing over the 
holes A B c D. In this example the plate had been exposed to 
the vapour of iodine, in such a manner that one zone had 
attained the fii'st coating of yeUow coloiu* ; a second zone had 
reached the red ; a third the blue and gi*een ; and a fourth 
having passed through all these tints, had obtained the second 
yellow coating. The number of white circular spots on each 
vertical zone indicates the degree of sensitiveness of the various 
coatings ; the less sensitive being the first coating of yellow, d, 
and the most sensitive the second yellow coating, a. This is 
sho^vn by the deposit of mercury on the plate i*epresented by 
the increased whiteness of the spots corresponding with the 
holes, each foui' vertical spots having been exposed for the same 
time to solar influence. 


M. Claudet has also devised a veiy ingenious uistniment for 
focusing, which he calls his Focimeter. (Fig. 22.) This it will 
be seen from the accompanying woodcut consists merely of 
segments of a circle, numbered and placed at fixed distances 
apart, upon a movable axis. This is copied by the camera on 
a plate or paper, and the result is shown in the annexed figure 
(23), in which it will be seen difierent degrees of eSect are sup- 
posed to have been produced. These determine the best focal 


point for any lens very readily, and it is really a most useful 
piece of apparatus in the hands of the photogi-apher. 


The Djmactinometer is thus described bj- the inventor : — It 
consists of a thin metallic disc, perfectly black, having a slit ex- 
tending fi-om its centre to the cii'cumference, fixed on an axis 
revolving tlirough a permanent metallic disc perfectly white. 
The white disc has also a slit from its centre of the exact length 
of the radius of the black disc ; and by means of these two sHts, 
which are so adjusted that the lilack disc can intersect the white 
disc, and by revolving, gradually cover the whole white area, 
the space of the wliite surfxce on which the black disc can be 
superposed forms itself a sort of dial, which is divided into any 
number of equal segments, all niimbered. The inventor has 
adopted the number of twenty segments for a large circle in- 
scribed on the dial, and of eight segments for a smaller circle, 
after the manner of the divisions of the Focimeter, but on the 
same plane. These eight segments are niimbered in geometrical 
progression, 1, 2, 4, 8, 16, 32, 64. 

The black disc may be made to revolve in such a manner that 
it shall cover a new segment of the large circle dvu-ing each 
second, or any other equal fraction of time. By that means the 
last segment will have received eight times more light than the 
first, the black disc having moved over the whole in eight 

The difierences of photogenic intensities are hardly observable 
when they follow the ai'ithmetical progression : the instrument 


is SO constructed that it may indicate the intensities in the 
geometrical progi-ession. The fii-st segment remains always 
covered, in order to be represented black on the dagiien'eotype 
plate and mark the zero of intensity : the second is exposed to 
li»ht dm-ino; V, the thii-d diu-inw 2". the fom-th during 4", the 
fifth diu'ing 8", the sixth during IG'', the seventh dui'ing 32", 
and the eighth diu-ing 64". This series, which could be extended 
by dividing the circle into a greater number of segments, is quite 
sufficient for all observations intended for practically measuring 
the intensity of the photogenic light, and for comparing the 
power of object-glasses. 

The instrument is made to move by applying the hand on a 
handle fixed on the back at the extremity of the axis on which 
the disc revolves. An ojjerator accustomed to count seconds 
by memory, or by following a seconds' beater, can perform the 
experiment with sufficient regularity ; but in order to render 
the instiTunent more exact and more complete, it can be made 
to revolve by clock-work, which gives it, at "s\t11, either the ai-ith- 
metical or the geometrical progi-ession. This last movement 
presented some difficulty; but the inventor has been able to 
obtam it without mnch complication in the machinery, and the 
apparatus is within the reach of the gi'eater number of operators 
having establishments on a complete footing. 

For the ins'tiiimeut moving by hand, it is necessary that a 
second person should open and shut the object-glass at a given 
signal. But in adapting before the object-glass a flap connected 
with a cord and pulley, the operator, holding the cord in the 
left hand, can open the flap at the moment that with the right 
hand he makes the disc revolve, and shut the apparatus when 
the revolution is complete. 

When the instrument acts by clock-work, the object-glass 
may be opened and shut by the same means, at the signal given 
by a bell which strikes at the commencement and at the end of 
the revolution. 

If a dagueiTeot}"iDe plate receive the image of the dynactino- 
nieter during its revolution, it is ob^-ious that each segment in- 
dicates an efifect in proportion to the intensity of light and to 
the time that it has remained uncovered; also that the number 
of seconds marked on the fii-st segment visible is the measure of 
the intensity of light at the moment of the experiment ; the 
efiect of each segment being in reality the degi-ee of intensity 
which can be obtained diu'ing the coiTCsponding time. 

^Tien we want to compare two object-glasses, they are adapted 
to two camerae obscm-ae placed before the dyuactinometer. 
After ha-ving set the focus of the two apparatus, they are 


charged each with a daguen-eotype plate or a photogenic paper. 
When all is ready, the flaps are opened at the moment that the 
dynactinometer commences its revolution, and they are shut 
when it is completed. The plates are removed and the images 
brought out. In comparing the result produced on each, it is 
easy to see which object-glass is the most rapid, and in what pro- 
portion. For instance, if the aritlimetical progression has been 
followed, and on one of the plates or papers the number 4 of 
the great cii-cle is the first \'isible, the conclusion is that it has 
been necessary for the intensity of the light at that moment to 
operate diu-ing four seconds in order to produce an efiect in the 
camera obscui'a; and if, on the other plate or paper, the first 
seven seomients have remained black, and the eighth segment is 
the first upon which the light has operated, the conclusion will 
be that the object-glass which has produced the efiect on the 
fii-st plate or paper has double the photogenic power of the 

But if the geometrical progression has been followed, the 
same experiment will show the image of the segment No. 3, re- 
presented on one plate, and that of the segment IsTo. 4 on the 
other, as having each the fii'st degi-ee of intensity : and we have 
to draw the same conclusion as regai'ds the power of each object- 

However, this conclusion woidd be exact only on the supposi- 
tion that the two plates were endowed with the same degree of 
sensitiveness : for if they had not been prepared identically in 
the same manner, we coidd not have the exact measure of the 
comparative power of the two object-glasses. The difierence 
might be due, not to any difference in the power of the object- 
glasses, but to the inequality in the sensitiveness of the two 
plates; although, in repeating the experiment several times, the 
mean result might be sufficiently conckisive. But this difficidty 
has not escaped the inventor, and he has tried to avoid it. 
Being able, by means of the photogi-aphometei-, to compare the 
sensitiveness of two plates under the action of the same in- 
tensity of light, and dimng the same space of time, he availed 
himself of this instrument to determine beforehand the compa- 
rative sensitiveness of the plates which are to be used in the 
experiment with the dynactinometer. By this means we can 
try beforehand several couples of plates, and keep them as it 
were stamped with their degree of sensitiveness imtil we want 
to apply them to test the power of two lenses. The impression 
is made on one-half of the plate, leaving the other half for the 
image of the dynactinometer. 

After having operated in the two camerse obscurae; each sup- 



])lied with the lenses the power of which we wish to compare, 
we submit the two plates, each impressed with both the photo- 
graphometer and dynactinometer, to the vapour of mercury, 
which developes the two images on each plate. 

The number of sj:)ots given by the photogi'aphometer, Fig. 20, 
will indicate the sensitiveness of the plate; and in comparing 
the two images given by the dynactinometer. Fig. 24, 25, 
accounting for the difference of sensitiveness of each plate, if 
there is any, we are able at once to determine the comparative 
power of the two lenses. 

For the practical investigation of this veiy important photo- 
graphic question, IMr. Knight has devised an apparatus that will 
be most valuable as affording the means of adjusting readily to 
the best focal distance. 

jVIr. Knight's apparatus consists in a frame having two 
grooves; one vertical, in which he places the gi'ound glass, and 

ii-lj c'— ^M 

'01 -m 

the other forming an angle with the first destined to receive 
the plate : the planes of the grooves intersect each other in the 
middle. After having set the focus upon the ground glass, this 
last is removed, and the plate is placed in the inclined gi-oove. 
Now, if a newspaper, or any large piinted sheet, is put before 
the camera, the image will be represented on the inclined plate ; 
and it is obvious in its inclination the various points of the 
plate will meet a different focus. The centre of the plate will 
coincide with the visual focus ; by its incKnation it will in one 
direction meet the photogenic focus at a point more or less 
distant from the centre, if the photogenic focus is shorter than 
the visual focus, and in the other dii-ection if it is longer. The 
frame is furnished with a scale of division, having the zero in 
the centre. When the image is represented on the daguerreo- 
type, by applying against it another movable scale of division 
similar to the other, the operator can find what is the division 


above or under zero, kt which the image seems best defined ; 
and after having removed from the camera the experiment frame, 
and set the focus as usual on the ground glass, he has only to 
move the tube of the object-glass by means of the rack and 
pinion, and to push it in or out ; a space corresponding with the 
division of the scale indicating the deviation of the true photo- 
genic focus: the tube of the object-glass is for that purpose 
marked with the same scale of division. 




Since the ciirious natiu-e of the results obtained, as I believe, by 
heat ratliations, have been supposed by some to belong to the 
same class of phenomena as those we have particularly under con- 
sideration, I am induced to introduce the subject in this treatise 
on photography, merely reprinting my original communication 
on the subject, as the investigations have not been continued. 

The. Journal of the Academy of Sciences of Paris, for the 18th 
of July, 1842, contained a communication made by M. Regnault 
fi'om M. Moser, of Konigsberg, " Siu' la Formation des Images 
Dagueri'iennes;"* in which he announced the fact, that " v^hen 
two bodies are sufficiently near, they impress their images upon 
each other." The Jounud of the 29 th of August contained a 
second communication from M. Moser, in which the residts of 
his researches are summed up iu twenty-six paragraphs. From 
these I select the following, which alone are to be considered on 
the present occasion : — 

" 9. All bodies ludiate light even in complete darkness. 

" 10. This light does not appear to be allied to phospho- 
rescence, for there is no difference perceived whether the bodies 
have been long in the dark, or whether they have been just 
exposed to daylight, or even to direct solar light. 

"11. Two bodies constantly impress theii* images on each 
other, even in complete darkness. 

•' 14. However, for the image to be appreciable, it is neces- 
sary, because of the divergence of the rays, that the tlistance of 
the bodies should not be very considerable. 

" 15. To render the image \'isible, the vapom- of water, mer- 
cuiy, iodine, &c., may be used. 

'•' 17. There exists latent light as well as latent heat." 

The anuoimcement at a meeting of the British Association 
of these discoveiies, natiu-ally excited a more than ordinary 
degree of interest. A discovery of tliis kind, changing, as it 
did, the featui-es, not only of the theories of light adopted by 

* Comptes Hendus, tome xv., No. 3, folio 1 19. 


pliilosopliers, but also the commonly received opinions of man- 
kind, was more calculated to awaken attention tlian anything 
which has been brought before the pubhc since the publication 
of Daguerre's beaiitiful photogi-aphic process. Having instituted 
a series of experiments, the results of which appear to prove 
that these phenomena are not produced by latent light, I am 
desirous of recording them. 

I would not be understood as denying the absorption of light 
by bodies; of this I think we have abundant proof, and it is a 
matter well deserving attention. If we pluck a nastui^tium when 
the sun is shining brightly on the flower, and carry it into a 
dark room, we shall still be enabled to see it hj the light which 
it emits. 

The human hand will sometimes exhibit the same phenomenon, 
and many other instances might be adduced in proof of the 
absorption of light ; and I believe, indeed, of the principle that 
light is latent in bodies. I have only to show that the conclu- 
sions of M. Moser have been formed somewhat hastily, being led, 
no doubt, by the striking similarity which exists between the 
effects produced on the daguerreotype plates imder the influence 
of light, and by the juxtaposition of bodies in the dark, to con- 
sider them as the work of the same element. 

1. Dr. Draper, in the PMlosopliical Magazine for September 
1840, mentions a fact which has been long known, — "That if a 
piece of very cold clear glass, or, what is better, a cold polished 
metallic reflector, has a little object, such as a piece of metal, 
laid on it, and the surface be bi'eathed over once, the object 
being then carefully I'emoved, as often as you breath on it 
again, a spectral image of it may be seen, and this phenomenon 
may be exhibited for many days after the fii'st trial is made." 
Several other similar experiments are mentioned, all of them 
going to show that some mysterious molecular change has taken 
place on the metallic surface, which occasions it to condense 
vapours unequally. 

2. On repeating this simple experiment, I find that it is 
necessary for the production of a good effect to iise dissimilar 
metals; for instance, a piece of gold or platina on a plate of 
copper or of silver "will make a very decided image, whereas 
copper or silver on their respective plates gives but a very faint 
one, and bodies which are bad conductors of heat, placed on 
good conductors, make decidedly the strongest impressions when 
thus treated. 

3. I placed upon a well-poUshed copper plate a sovereign, a 
shilling, a large silver medal, and a penny. The plate was 
gently warmed by passing a spirit-lamp along its under siu-face : 



when cold, the plate was exposed to the vapour of merciuy : 
each piece had made its impression, but those made by the gold 
and the large medal were more distinct ; not only was the disc 
marked, but the lettering on each was copied. 

4. A bronze medal was supported upon slips of wood, placed 
on the copper, one-eighth of an inch above the plate. After 
mercui'ialization, the space the medal covered was well marked, 
and, for a considerable distance aroimd, the mercury was un- 
equally deposited, giving a shaded border to the image ; the 
spaces touched by the merciuy [?] were thickly covered ^dth the 

5. The above coins and medals were all placed on the plate, 
and it was made too hot to be handled, and allowed to cool 
without theii" being removed ; impressions were made on the 
plate in the following order of intensity, — gold, silver, bronze, 
copper. The mass of the metal was found to influence ma- 
terially the result ; a large piece of copper making a better 
image than a small piece of silver. When this plate was 
exposed to vapour, the results were as before. On rubbing oflT 
the vapoui-, it was found that the gold and silver had made per- 
manent impressions on the copper. 

6. The above being repeated with a still gi-eater heat, the 
image of the copper coin was, as well as the others, most faithfully 
given, but the gold and silver only made permanent impressions. 

7. A silvered copper plate was now tried with a moderate 
warmth. Mercuiial vapoui^ brought out good images of the 
gold and copper ; the silver marked, but not well defined. 

8. Having repeated the above experiments many times with 
the same results, I was desii-ous of ascertaining if electricity had 
any similar effect : powei-ful discharges were passed through and 
over the plate and discs, and it was subjected to a long-continued 
ciu-rent without any effect. The silver had been cleaned off 
from the plate ; it was now waiTaed with the coins and medals 
upon it, and submitted to discharges from a very large Leyden 
jar : on exposing it to mercui'ial vapoiu*, the impressions were 
veiy prettily brought out, and, strange to say, spectral images 
of those which had been received on the plate when it was 
silvered — thus proving, that the influence, whatever it may 
be, was exerted to some depth in the metal. 

9. I placed upon a plate of copper, blue, red, and oi-ange- 
coloured glasses, pieces of crown and flint glass, mica, and a 
square of tracing paper. These were allowed to remain in con- 
tact half an hoiu-. The space occupied by the red glass was well 
marked ; that covered by the orange was less distinct, but the 
blue glass left no impression ; the Shapes of the flint and crown 


glass were weU made out, and a remarkably strong impression 
where the cro^vn glass rested on tlie tracing paper, but the mica 
had not made any impression. 

10. The last experiment repeated. After the exposm-e to 
mercmial vapoiu', heat was again applied to dissipate it : the 
impression still remained. 

11. The experiment repeated, but the vapour of iodine used 
instead of that of mercury. The impressions of the glasses ap- 
peared in the same order as before, but also a very beautifid 
image of the mica was developed, and the paper well marked 
out, showing some relation to exist between the substances used 
and the vapours applied. 

12. Placed the glasses used above, with a piece of well-smoked 
glass, for half an hour, one-twelfth of an inch below a polished 
plate of copper. The vapour of mercury brought out the image 
of smoked glass only. 

13. All these glasses were placed on the copper, and slightly 
warmed : red and smoked glasses gave, after vaporisation, 
equally distinct images, the orange the next, the others left but 
faint max'ks of theu* forms ; polishing with Tripoli and putty 
powder would not remove the images of the smoked and red 

1 4. An etching, made upon a smoked etching ground on glass, 
the copper and glass being placed in contact. The image of the 
glass only could be brought out. 

15. A design cut out in paper was pressed close to a copper 
plate by a j)iece of glass, and then exposed to a gentle heat ; the 
imjiression was brought out by the vapour of mercury in beauti- 
fid distinctness. On endeavouring to rub off the vapour, it was 
found that all those parts which the paper covered amalgamated 
with mercmy, which was rubbed j&'om the rest of the plates : 
hence thei-e resulted a perfectly white pictiu'e on a polished 
copper plate. 

16. The coloured glasses before named were placed on a plate 
of copper, with a thick piece of charcoal, a copper coin, the mica, 
and the paper, and exposed to fervent simshine. Mercuidal 
vapour brought up the images in the following order : — Smoked 
glass, crown glass, red glass, mica beautifully delineated, orange 
glass, paper, charcoal, the coin, blue glass — thus distinctly 
proving that the only rays which had any influence on the metal 
were the calorific rays. This experiment was repeated on 
different metals, and "svith various materials, the jDlate being ex- 
posed to steam, mercuiy, and iodine : I invariably found that 
those bodies which absorbed or permitted the permeation of the 
most heat gave the best images. The blue and violet rays 


could not be detected to leave any evidence of action, and as 
spectra imprinted on pliotogi-apliic papers by light, wliicli had 
permeated these glasses, gave evidence of the lai"ge quantity of 
the invisible rays which passed them freely, we may also consider 
those as entirely without the power of effecting any change on 
compact simple bodies. 

17. In a paper which I pubhshed in the Philosophical Maga- 
zi7ie for October, 1840, I mentioned some instances in which I 
had copied printed paper and engravings on iodized paper by 
mere contact and exposm-e to the influence of calorific rays, or 
to artificial heat. I then, specvilating on the probability of our 
being enabled, by some such process as the one I then named, 
to copy pictiu'es and the like, proposed the name of Thermo- 
graphy, to distiuguish it from Photography. 

18. I now tried the effects of a print in close contact wdtli a 
weU-polished copper plate. When exposed to mercvuy, I found 
that the outline was very faithfidly cojiied on the metal. 

19. A paper ornament was pressed between two plates of 
glass, and wai-med j the impression was brought out with toler- 
able distinctness on the imder and warmest glass, but scarcely 
traceable on the other. 

20. Rose leaves were faithfully copied on a piece of tia plate, 
exposed to the full influence of sunshine ; but a much better 
impression was obtained by a jDrolonged exposure in the dark. 

21. With a view of ascertaining the distance at which bodies 
might be copied, I placed upon a plate of polished copper a thick 
piece of plate-glass, over this a square of metal, and several other 
things, each being larger than the body beneath. These were 
all covered by a deal box, which was more than half an inch 
distant fi'om the plate. Things were left in this position for a 
night. On exposing to the vapoiu- of mercury, it was found that 
each article was copied, the bottom of the deal box more faith- 
fully than any of the others, the grain of the wood being imaged 
on the plate. 

22. Having found, by a series of experiments, that a black- 
ened paper made a stronger image than a white one, I very 
anxiously tried to effect the copying of a printed page or a print. 
I was partially successful on several metals ; but it was not 
imtil I used copper plates amalgamated on one siirface, and the 
mercury brought to a very high polish, that I produced any- 
thing of good promise. By carefully preparing the amalga- 
mated surface of the copper, I was at length enabled to copy 
from papei', line-engravings, woodcuts, and lithographs, with 
surprising accui-acy. The first specimens produced exhibited a 
minuteness of detail and shai-pness of outline quite equal to 


tlie early daguerreotypes and the pliotogi-aphic cojiies prepared 
with the chloride of silver. 

The following is the process adopted by me, which I consider 
far from perfect, but which affords us very delicate images : — 

A well-poHshed plate of copper is rubbed over with the nitrate 
of mercury, and then well washed to remove any nitrate of 
copper which may be formed ; when quite dry, a little mercury 
taken up on soft leather or linen is well rubbed over it, and the 
sm-face worked to a perfect mirror. 

The sheet to be copied is placed smoothly over the mercurial 
surface, and a sheet or two of soft clean pajjer being placed upon 
it, is pressed into equal contact with the metal by a piece of 
glass, or flat board : in this state it is allowed to remain for an 
hour or two. The time may be considerably shortened by 
apjjlying a very gentle heat for a few minutes to the under 
surface of the plate. The heat must on no account be so great 
as to volatilise the mercury. The next process is to place the 
plate of metal in a closed box, prepared for generating the vapoirr 
of mercury. The vapour is to be slowly evolved, and in a few 
seconds the picture will begin to appear ; the vapoiu- of mercury 
attacks those pai-ts which correspond to the white parts of the 
pi'inted page or engraving, and gives a very faithful but some- 
what indistinct image. The plate is now removed from the mer- 
curial box, and placed into one containing iodine, to the vapour 
of which it is exposed for a short time : it will soon be very 
evident that the iodine vapour attacks those parts which are 
free from mercurial vapour, blackening them. Hence there 
results a perfectly black picture, contrasted ■wdth the gray ground 
formed by the merciu-ial vapour. The picture being formed by 
the vapom's of mercury and iodine, is of course in the same state 
as a daguerreotype picture, and is readily destroyed by rubbing. 
From the dej^th to which I find the impression made in the 
metal, I confidently hope to be enabled to give to these singular 
and beautiful productions a considerable degree of permanence, 
so that they may be used by engravers for working on. 

It is a cm-ious fact that the vapours of mercury and of iodine 
attack the plate difierently ; and I believe it will be found that 
vajjours have some distinct relation to the chemical or thermo- 
electrical state of the bodies upon which they are received. 
Moser has observed this, and attribvites the phenomena to the 
colours of the rays, which he supposes to become latent in the 
vapour on its passing from the solid into the more subtile form. 
I do not, however, think this explanation will agree with the 
results of experiments. I feel convinced that we have to do 
with some thermic influence, and that it will eventually be fovmd 


that some purely calorific excitement produces a molecular 
change, or that a thermo-electric action is induced which effects 
some change in the polarities of the idtimate atoms of the solid. 
These are matters which can only be decided by a series of 
well-conducted experiments ; and, although the subject will not 
be laid aside by me, I hope the few curious and cei-tainly im- 
portant facts which I have brought before you, "s\-ill elicit the 
attention of those whose leisure and well-known experimental 
talents qualify them in the highest degree for the interesting- 
research into the action of those secret agents wliich exert so 
powerful an influence over the laws of the material creation. 
Although attention was called to the singailar manner in which 
vapours disposed themselves on plates of glass and copper, two 
years since, by Dr. Draper, Professor of Chemistry at New 
York, and about the same time to the calorific powers of the 
solar spectrum, by Sir John Hei'schel,* and to the influence of 
heat artificially applied, by myself, yet it is certainly due to M. 
Moser, of Konigsberg, to acknowledge him to be the first who 
has forcibly called the attention of the scientific world to an 
inquiry which promises to be as important in its residts as the 
discovery of the electropile by Yolta. 

As to the practical utility of this discovery, when we reflect 
on the astordshing progress made in the ai't of Photography 
since Mr. Fox Talbot published his fii-st process, what may we 
not expect from Thermography, the fii-st mde specimens of 
which exhibit far greater perfection than the early efforts of the 
sister art ? 

Asa subject of purely scientific interest, thermography promises 
to develop some of those secret influences which operate in the 
mysterious arrangements of the atomic constituents of matter, 
to show us the road into the yet hidden recesses of nature's 
works, and enable us to pierce the mists which at present 
envelope some of the most striking jjhenomena which the 
penetration and industry of a few " chosen minds" have brought 
before oui' obsciu'ed visions. In connection with photogi-aphy, 
it has made us acquainted with subtile agencies working slowly 
but surely, and indicated physical powers beyond those which 
are already known to us, wliich may possibly belong to a more 
exalted class of elements, or powers, to which Light, Heat, and 
Electricity are subsidiary in the great phenomena of Natm-e. 

* Philosophical Transactions, Part I., 1840, p. 50. 



Few speculations are more replete with interest than that of the 
jjrobability of onr succeeding in the production of photogi-aphic 
images in their local colours. M. Biot, a great authority, says, — 
" Substances of the same tint may present, in the quantity, or 
the uatm*e of the radiations which they reflect, as many diversities, 
or diversities of the same order, as substances of a different tint ; 
inversely, they may be similar in their property of reflectiug 
chemical radiations when they are dissimilar to the eye ; so that 
the difference of tint which they px'esent to the eye may entirely 
disappear in the chemical pictui-e. These are the difficulties in- 
herent in the fonnation of photogi'aphic pictui'es, and they show, 
I think, evidently, the illusion of the experimenters who hope to 
reconcile, not only the intensity, but the tints of the chemical 
impressions produced by radiation, with the colours of the objects 
fi-om which these rays emanate." It may be remembered that 
two years since, Sii- John Herschel succeeded in procm-ing upon 
photogi'aphic paper a coloured image of the solar spectrum ; and 
that emment inquirer has commimicated to me a recent discoveiy 
of great interest, which I have his permission to publish. " I 
have got specimens of paper," says Sii" John Herschel, " long 
kept, which give a considerably Ijetter rej^resentation of the 
spectrum in its natural colours than I had obtained at the date 
of my paper (Febrviary 1840), and that light on a dark ground ; 
but at present I am not prepared to say that this will prove an 
available process for coloured photogTaphs, though it brings the 
hope ne((/rer." Here we have the speculations of one philosopher 
representing the production of such pictures as hopeless, while 
the experiments of another prove these to be within the range 
of probabilities. 

My ovm experiments have, in many instances, given me 
coloui'ed pictiu-es of the prismatic spectrum, dark upon a light 
ground, but the most beautiful I have yet obtained has been 
upon the daguerreotype iodidated tablets, on which the colours 


have, at the same time, had a peculiar softness and brilliancy. 
Daguerre himself has remarked, that when he has been copying 
any red brick or painted building, the photograph has assumed 
a tint of that character. I have often obsei-ved the same thing 
in each variety of photogi*aphic material, i.e., where a salt of 
silver has been used. In the Philosojyhical Magazine for April 
1840, will be found a paper, — " Experiments and Observations 
on Light which has permeated Coloured Media," — in which I 
describe some ciu'ious x-esults on some of those photogTaphs 
which are prepai'ed with the hycModic salts exposed to limiinous 
influence with coloiu'ed fluids superimposed ; permitting, as 
distinctly isolated as possible, the permeation of the violet and 
blue, the gi'een, the yellow, and the red rays, under each of Avhich 
a complementaiy coloui" was induced. Diu-ing January of the 
present year, I prepared some papers with the bichromate of 
potash and a very weak solution of nitrate of silver : a piece of 
this paper was exposed behind foiu- coloiu-ed glasses, which 
admitted the passage respectively of, 1st, the violet, indigo, and 
blue rays ; 2d, the blue, the green, and a portion of the yellow 
rays ; 3d, the green, yellow, and orange rays ; and, 4th, the 
orange and red rays. The weather being extremely foggy, the 
aiTangement was unattended for two days, being allowed to lie 
upon a table opposite a -ttTiidow having a southern aspect. On 
examining it, it had, imder the respective colour's, become tinted 
of a blue, a green, and a red : beneath the yelloAv glass the 
change was uncertain, from the pecuKar coloiu' of the paper, and 
this without a single gleam of sunshine. My numeroiis engage- 
ments have prevented my rei^eating the observations I desii^e on 
this salt, which has hitherto been considered absolutely insensible 
to light. 

The baiytic salts have nearly all of them a peculiar caloiific 
efiect ; the miuiate, in particidar, gives rise to some most rich 
and beautiful crimsons, particularly under the influence of light 
which has permeated the more delicate gi-een leaves ; and also in 
copymg the more highly-colom^ed flowers, a variety of tintings 
having been observed. We may always depend on producing a 
photograpliic copy of a leaf of a green colovir by the following 
an-angement : — HaA-ing silvered a copper plate, place it in a 
shallow vessel, and lay thereon the leaf of which a copy is 
desu-ed, maintaining it in its position by means of a piece of 
glass j poiu' upon it, so that the plate beneath the glass may be 
covered, a solution of the hydriodate of potash, containing a little 
fi'ee iodine : then expose the whole to simshine. In abottt half 
an hour, one of the most beautiful photographic designs which 
can be conceived is produced, of a fine green yellow. The fluid 


is yellow, and cuts off nearly all tlie " chemical" rays, allowing 
only of the free passage of the less refrangible rays ; the most 
abundant being the yellow. This retards the process of solariza- 
tion, but it produces its complementary coloiu- on the plate. 

These facts will, I think, prove that the possihility of our being 
enabled to produce coloiu-ed photographs is decided, and that 
the probabiliti/ of it is brought infinitely nearer, particularly by 
Sfr John Herschel's very important discovery, than it was 
supposed to be. 

M. Edmond Becquerel has recently succeeded in obtaining 
bright impressions of the spectrum in colonics, and copying highly 
coloured drawings on metallic plates prepared with chlorine. 
The results of M. Niepce de St.-Victor have been of a satisfactory 
character : the main particulai-s thereof we select from a memoir- 
entitled " Upon the Relation existing between the Coloiu-s of 
certain colom-ed Flames with the Heliographic Images colom'ed 
by Light." 

When a plate of silver is plunged into a solution of sulphate 
of copper and chloride of sodium, at the same time that it is 
rendered electro-positive by means of the voltaic battery, the 
chloride fonned becomes susceptible of colouration, when, having 
been withdrawn from the bath, it i-eceives the influence of 

M. Niepce de St.-Victor, from obsei'ving that when chloride 
of sodium (common salt) was employed, the plate became more 
susceptible of receiving a yellow colour than any other, and 
knowing that it impai'ted a yellow colour to flame, was led to 
believe that a relation existed between the colour communicated 
by a body to flame, and the coloiu- develojjed upon a plate of 
silver, which should have been cHoridated with the particular 

To avoid complexity, it may be briefly stated that the bath in 
which the sensitive sm*face is obtained is prepared with water, 
holding free chlorine in solution, to which has been added the 
salt which is essential to give a ^predominance to any particular 

It is well known that strontiau gives a purple colour to flames 
in general, and to that of alcohol in particular. If we prepare a 
plate of silver and pass it into water saturated with chlorine to 
which is added some chloride of strontian, and when thus pre- 
pared we place upon it a coloured design of red and other colom-s, 
and then expose it to the sunsliine, after six or seven minutes 
we shall perceive that the colours of the image are reproduced 
upon the plate, but the reds much more decidedly than the 
others. When we would produce successfully the other rays of 


the solar spectram, we operate in the same manner as we have 
indicated for the red i-ay — employing for the orange the chloride 
of calcium, or that of uranium for the yellow, or the hyjiochlorite 
of soda, or the chlorides of sodium or potassium. Yery fine 
yellows have been obtained with a bath composed of water 
slightly acidulated with muriatic acid and a salt of copper. 

The green rays are obtained with boracic acid or the chloride 
of nickel ; also with all the salts of copper: The blue and indigo 
I'ays are obtained with the double chloride of copper and ammonia. 
The violet rays are obtained with the chloride of strontian and 
sulphate of copper. Those substances which give white flames, 
as the chloride of antimony, the chloride of lead, and the chloride 
of zinc, yield no colour by kmiinous action. All the colours of 
a pictm-e have been produced by preparing a bath composed of 
the deuto-chloride of copper ; and M. Niepce states that this 
salt thrown into burning alcohol produces a variegated flame 
according to the intensity of the fire, and it is nearly the same 
with all the salts of copper mixed with cliloriue. ZS^iepce says — 
" If we put a salt of copper in liquid chlorine we obtain a very 
sensitive sm-face by a single immei'sion in the bath ; but the 
colorific result of this mixture is seldom good. I prefer a 
mixture of equal parts of chloride of copper and of chloride of 
iron, with thi-ee or four parts of water ; the cliloride of iron has, 
as those of copper, the property of being impressed on the plates 
of silver and of producing many colours, but they are infinitely 
more feeble, and the yellow always predominates ; and this agrees 
with the yellow colour produced in flame by this salt." 

It should be understood that when the plate of silver, being 
previously connected with a voltaic battery, is phmged into the 
bath and the circuit completed, it becomes covered with a dark 
coating, probably of a sub-chloride of silver mixed ^vith the salt, 
on wluch the colour to be produced by solar radiation depends. 

If we form a bath composed of all the substances which 
separately give a dominant colom-, we obtain veiy lively colours ; 
but the great difficulty is the mixing of the salts in such propor- 
tions as to give an equality to the tints, as it commonly happens 
that some colom's are excluded by others. We cainiot always 
depend upon obtaining the same results with the same materials, 
owing principally to the diflicrJty of preserving the solution at 
a uniform strength. Liquid chlorine is necessary — the application 
of dry chlorine ^\t11 not produce the same results, and the volatile 
chlorine is continually escaping from the water. 

Niepce de St.-Victor has made many experiments to produce 
the colours upon salts of silver and copper spread on paper, but 
without success; the metallic plate appears absolutely necessary, 


and the pui-er the silver the more perfect and intense is the 
impression. The following is recommended as the most effectual 
mode of manipulating. The sUver plate is highly polished with 
the best tripoli powder and ammonia ; being perfectly cleaned it 
is connected with the battery, and then plunged into the bath 
prepared in any of the ways stated. It is allowed to remain in 
the bath for some minutes, taken from it, washed in a large 
quantity of watex*, and dried over a spu-it-lamp. The surface 
thus produced is of a dull neutral tint, often almost black ; the 
sensibility of the plate ajjpears to be increased by the action of 
heat, and when brought by the spiiit-lamp to the cerise red 
colour it is in its most sensitive state. The sensibility, how- 
ever, of the plates is low, two or three hours being requii'ed to 
produce a decided effect in the camera obscura. The name of 
Heuochromes has been given to these naturally coloiu'ed 
photographs, some of which, the personal gift of the inventor to 
Mr. Malone, I have inspected. These, when I fii-st saw them, 
were perfectly coloiu-ed in correspondence with the drawings of 
which they were copies ; but the colours soon faded, and it does 
not appear as yet that any successfid mode of fixing the colours 
has been discovered. 



It is to the photographic artist, a matter of considerahle 
momeut that he undei-stands the principles upon which his 
instmments are constnicted. It has, therefore, been thought 
advisable to add a short chapter which should give a sufficiently 
popular explanation of the dioptrical phenomena '«dth which we 
have especiaUj to deal. 

Upon the refractive power of the media employed, depends 
the perfection of the results we obtain ; thei'efore, some of the 
phenomena of refraction, or breaking back, as the term implies, 
should be clearly understood. 

A ray of light passing though a vacuum progi-esses in a 
perfectly straight Hne, and we shoidd, if we lookecl at a brilliantly 
illuminated point — were it possible — imder such conditions, see 
it in its ti-ue position, the numerous rays coming undisturbed 
directly to the eye. But all matter, however attenuated it may 
be, has the property of refracting, or bending the ray of light ; 
consequently we do not see the stai-s in their ti-ue position, owing 
to the refractive power of the atmosphere. 

The most simple illiLstration of refraction is to allow a sun- 
beam, a, passing through a small hole in the window-shutter of 
a dark room, to fall upon the siuface of a fluid contained in a 
glass vessel, b b : instead of proceeding onward to a, it will be 
found to alter its course at the siu-- 
face of the fluid, and pass along the 
line to a a. Every substance has 
different refractive powers in virtue 
of its physical constitution ; but a 
ray of light incident perpendicularly 
on a refecting medium, as the ray c, 
(Fig. 27) sufiei-s no refraction. If we 
float, one upon the other fluids, b,c,d, 
having cUfierent powei-s of refi-action 
we shall then see the relative phenomena exhibited by the 



bending of the ray a a, in passing tln-ough tliem (Fig. 28). 

It will be evident tbat no great 
difficulty exists in measuring tbe 
refractive powers of diflerent trans- 
parent bodies : and that hence we 
are enabled to tabulate those which 
have the highest and lowest refrac- 
tive indices. A few of the most 
impoi-tant are given in the following 
table : — 




Oil of Cloves 

Crown glass 

Plate glass 

Flint glass 

Do. containing much lead 










This knowledge enables us to trace a ray of light through 
transparent bodies of any form, provided we can find the incli- 
nation of the incident ray to the sui'face, where it either enters 
or quits the body. 

If parallel rays fall upon a plane sm-face G, of glass, they will 
retain their parallelism after passing through it as the ray A 
(Fio-. 29). The rays diverging from the point A, will be refracted 

by the first surface into the 

directions h b, and by con- 
tinuing a a, and b b, back- 
wards, we shall find they 
meet at a point beyond A : 
so that supposing the eye 
to be placed within the 
body G, the point A would 
appear removed to B. But 
when the rays undergo a second refraction by passing out of 
the second surface, we shall find by continuing the lines back- 
wards that they meet at c ; therefore a plane glass diminishes 
the apparent distance of the point of the diverging rays. If, 
instead of a plane glass, we employ a piece equally curved, 
like a watch-glass, it produces very little change in the form 
and position of objects. 

Lenses are glasses ground to difiei-ent foi-ms, their- sui-faces 
being segments of spheres, and it is in obedience to the i-efrac- 



tory power of the surfaces so produced that their peculiarities 
belong. The adjoining figui-es represent the varieties. 


1 is termed a plano-convex lens. 

2 is a double convex lens. 

3 is formed of parts of two circles of different diameters, 
and is called a meniscus lens, or concavo-convex. 

4 is a plano-concave lens. 

5 is a double concave lens. And 

6 is a concavo-convex lens, fonned of parts of the inner sur- 
faces of two dissimilar circles. 

It is not necessary to examine the laws of refi'action for all 
these forms ; the phenomena will be fiilly understood by an 
examination of a few leading points. Whatever may be the 
form of a lens, the incident rays pai-aUel to its axis pass 
through without suffering refraction, as a a a, a a a, Fig. 31. 

All other rays mxxst have a certain amoxmt of obliquity, and 
these all consequently suffer refraction, as the rays a a. Now 


tlie rays B B, and the ray c c, are refi-acted, and meet at D d' ; 
tlie line h h represents the focal image produced of the body 
from which the light proceeds. 

In the last figiire the image produced l^y the lens is repre- 
sented as cm'ved : a little consideration Avill show that it is not 
possible that such a cm-ved surface as that represented could 
produce an image of equal distinctness over every ^yart of a 
plane surface : the rays cannot meet, as they are refracted from 
curved sm-faces along any straight line, as F F F ; and supposing 
we receive on the sui"face of a lens a bright circular image, it 
will be brilliant and well defined around the centre, the light 
becoming fainter towards the edge, and at length passing into a 
cloudy halo, exhibiting the prismatic colours. This is called 
spherical aberration, and to it is due that want of distinctness 
which commonly is found around the edges of pictures taken in 
the camera obscvira. 

It is therefore important, in the selection of lenses, that we 
look for sharpness of definition over the tvhole of a perfectly 
flat field. To manufacture a lens which shall effect this, is a 
task of some difficulty ; but by attention to the two facts, that 
a lens, one surface of which is a section of an ellipse, and the 
other of a circle struck from the farthest of the two foci of that 
ellipse, as in Fig. 32, produces no abeiTation, much may be 

» effected. A meniscus 

lens, therefore, with 
a convex sui'face, part 
of an ellipsoid, the 
focal distance of which 
coincides with its far- 
ther focus, and a con- 
cave svu"face, part of a 
sphere, whose centre 
is that focus, will 
meet all oxvc require- 
ments. The mecha- 
nical difficulties of producing such lenses are great, but they 
may, by cautious manipulation, be to a great extent over- 
come. There are other methods by which the aberration of 
sphericity may be corrected, but for a description of these the 
reader is referred to Su- Jolin Herschel's Treatise on Light, in 
the Encyclopxjedia Metropolitana. 

If we take such a lens as we have been describing, and stop 
its centre with a blackened disc, leaving only a small portion of 
the edge for the light to pass through, and throw its image on 
a screen, we shall find it will be bordered with fringes of 


coloiu'. At one distance red will ijrevail, at another violet. 
This is the result of chromatic aberration, and arises from the 
unequal refrangibility of the dissimilar rays. The red rav is 
less bent than the \'iolet ; consequently, supposing the rays r r 
to fall on the edge of a lens, they will converge to a point 




at F, whereas if the rays v v fall along the same circular line, 
they will, being more refracted, meet at f. Now if we place a 
disc at e, just the size of the cone of light, it will be edged -svith 
■violet, but if we move it to a, the coloured border will be i-ed. 

The indices of refraction for the several rays have been most 
carefully determined by Fraimhofer, and for a standard medium, 
a flint glass prism, they are respectively 

Red 1-627749 dark Hue B 

Orange 1-629681 C 

YelloV 1-635026 D 

Green 1-642024 E 

Blue 1-648260 F 

Indigo 1-660285 G 

Violet 1-671062 H 

Fraunhofer has determined the absolute values from the fixed 
dark lines which he observed in the spectrum : they represent, 
however, very closely the rays distinguished by their colom*s. 

By refen-ing to the table of the refractive powers of trans- 
parent bodies (page 164), it will be seen that for a beam of 
white light, the difference between the most refr-actory flint 
glass and crown glass, in their refracting powers, is as 2-028 is 
to 1.5-34, and this j^roportion is maintained nearly, but not 
exactly, for all the coloui-ed rays : if, therefore, we have a cro-wna 

glass lens, the refractive power of which will place the focus 
at a, for the violet rays, and at b, for the red rays, and we grind 


to ±ii it a riint glass lens, the refractory power of -wliich wotild 
place the foci of the rays at c, d, it will be seen that the result 
of such a combination would be the formation of a colourless 
image, at a mean point between them, by recombining the rays 
into white light. Such as is represented in the figure Ls the 
achromatic lens of a camera obscura. 

There is, however, a point to be examined in connection with 
the lens for photogi-aphic purposes, which is of the fii-st im- 
portance, and which has not hitherto been sufficiently attended 
to. It is this. The luminous and coloured rays of the spectmm, 
and the chemical rays, are not coincident at any point of the 
.spectral image, and the relation between the chemical power, 
and the illuminatiug power, of a ray, Ls subject to constant 

It is often stated that the violet and blue rays are the 
chemical rays, and hence it is infeiTed, if the glass of a camera 
is corrected so as to make these rays, and the less refrangible 
red, to correspond, all is done which can be desired. 

It must be distinctly undei-stood that the coloiu' of any par- 
ticular ray has no direct relation to its chemical character. It 
is true, if the more refrangible rays are made to coiTCspond 
with the more luminous rays, we approach the desired point, 
but we do not neeessai^ily reach it. The following remarks from 
a paper read by the author before the Photographic Society of 
London will explain this point. 

I need not go pailiculai-ly into the conditions necessary to 
ensure the recombination of the particular rays produced by 
refraction. When we look thi-ough an ordinary single lens, or 
a bad telescope, we find all objects are fringed with colour — we 

have chromatic dispersion — and this arises from the circumstance 
that every one of the coloured rays has a distinct and separate 


focal distance. Hence tlie object of a combination of lenses is to 
bring the coloured rays to one point, wbere they are reunited 
into white light. If we bring the face of one prism up against 
the face of another, we i-ecombine those prismatic rays which 
would be produced by refraction in one du'ection, and obtain a 
spot of white light by such recombination. I have endeavoured to 
show, in the accompanying figure, something like the resxilt that 
takes place. We start with a coloured image whose parallel 
rays fall upon a lens of flint glass, that lens representing virtually 
two prisms placed with two of their faces together. Supposing 
we use a double convex lens, representing the conditions of two 
prisms placed edge to edge, we should vii*tually produce achro- 

In this way the lenses have been corrected for colovir, but this 
correction for colour does not include the necessary correction 
for ensuring the coincidence of the chemical and the luminous 
rays. Supposing the correction has been made for all the 
chromatic rays from the dark line A to the line H in the violet, 
there still remains an outlying set of radiations, nearly equal in 
leng-th to the space between A and H, and over this space the 
actinic force is more particularly active. Now, in ordinary 
achromatic lenses, the focus of these rays of high refrangibility 
must fall nearer the inner surface of the lens than the true 
luminous focus. This was fii-st noticed in achromatic lenses by 
Mr. Claudet. The fact for ordinary meniscus lenses, was in the 
first instance pointed out by Mr. Towson, who, in a paper 
published in the Philosojyhical Magazine, showed, that if, having 
obtained the best visual image, with a non-achromatic lens in 
the camera, we then put the prepared plate or paper about a 
quarter of an inch nearer the glass, when the focal distance is 
about 12 inches, an infinitely better photograph is obtained than 
that produced by the best visual image. Mr. Claudet's observa- 
tions on this point were also published in the Philoso2)hical 
Magazine for 1844, and may be referred to with advantage, as 
containing some very imporfant observations on this matter. 
He showed that even wdth achi'omatic lenses the visual focus and 
the chemical focus were not coincident. He states that with 
some lenses he fovmd the focus was nearer the glass, and sometimes 
it was fiu'ther from the glass, than the visual focus. It is rather 
difficult to understand why this shoiild be, u.nless the glasses 
had in one case been " over-corrected," and in the other that they 
had been " under-corrected." Suppose we have the lens corrected 
accurately for chromatic dispersion so as to bring the line H and 
the line A coincident the one with the other, the residt would 
be that the chemical rays would fall still nearer the inner surface 

170 scirvriFic rs'A'ESTiGATioxs on photography. 

of the lens. And it will be found by a very cai-eful adjustment 
of tlie camei-a, jDai-ticiilaiiy wliere single aclii-omatic lenses are 
employed, if we tiy two expeiiments, obtaining one picture at 
the plane giving the finest visual image, and then another at a 
very short distance nearer the lens, that a finer definition in the 
detailed part of the picture will be produced in a shoiter time 
in the last experiment, all the other conditions being the same, 
than in the fii'st. Let it be clearly iinderstood that we have, and 
require, the achi'omatic combination of glasses for producing 
white light : the coincidence of the rays from the coloiu'ed bodies, 
as sho-wn along the slightly cui'ved line, in fig. 3-5. But the 
chemical i-atUations from the same object would fall upon the line, 
which cuts the cui've of liuninous intensity, so that the best 
chemical efiect would be produced along that line. Though in 
ordinary cases, this is but a very minute distance neai-er the 
inner sui-fece of good achromatic lenses, it is quite certain that 
a difference does exist, and to this it is most important that 
attention shoidd be given. With regai'd to the piinciple, there- 
fore, that should regulate the constmction of the lenses for 
photogi-aphic purjwses, we should, to a certain extent, set aside 
the idea of achi-omaticity. We shoidd not only correct oui* 
lenses for coloiu', but we should coiTect them for the pecvdiar 
principles with which, combined in action, we have to deal. 
The chemical radiations do not aflect the eye as the colom-ed 
i"adiations do ; we can detect them only by the phenomena 
of chemical change. They come to the eye associated with 
colovu' from the coloiu-ed objects external to \is or to oui' camei-a. 
TNTiatever they may be, I have afready shown on several 
oc<jasions that Lifjht acts as a positively retarding agent in all 
the changes which take place on oiu- photogi'aphic prepai'ations ; 
therefore, by throwing the colom-ed rays even out of focus, we 
may reaUy produce a perfect photogi-aphic picture in less time 
than when the light-rays intei'fere. It appears to me clear that 
■we ought to consider the chemical sj^ectinun as distinct and 
separate in all respects from the luminous spectnim, Ijiit, like 
that limiinous spectiimi, as made up of bands of different re- 
fi'angibility. In this manner M. Melloni distingTushes the 
calorific spectnim as possessing a set of rays which he calles ther- 
mochroic rays, or rays coloui'ed for heat ; those heat-i^ays, 
which ai-e indicated in Sii' John Hei'schel's experiment, being 
analogous to those fr'om coloui*ed rays produced fr'om the spectral 
image of a round hole, through which the luminous pencil is 
admitted. The chemical spectnim, on what ever material obtained, 
exhibits an analogous order of refi-angibility. — ^the same degrees 
of variation of intensitv, and a similar an^ansjement of fonn. It 


becomes of course important, and it is the only means by wliich 
photographers can work effectively, that they should obtain 
lenses which ttlU give, at the same time, the most perfect visual 
image that can be produced (so far achromaticity is an object to 
be desired, and one "we always mitst attain), and be correct for 
the actinic focus. Indeed, in doing this, we must of necessity 
produce a lens which is not merely achromatic, but really 
orer-achromatic. Now instead, therefore, of correcting for the 
line H in the violet ray, or any particular line in the ordinary 
spectrum, it becomes, from all that we know, essential to correct 
for those lines recently discovered by 3Ir. Stokes, beyond the 
extreme lavender ray of the Xewtonian spectitmi, or else we 
leave a considerable portion of the chemical rays out of the 
sphere of action. Therefore, it appears to me, under considera- 
tion of the conditions I have endeavoui-ed to explain, that it 
would be convenient that we should adopt for the chemical 
principle of the sunbeam, Acttstsm, that which MeUoni has 
done for Heat. We should establish a nomenclature by which 
we should get rid of terms that we do not correctly express things 
that we have to deal with. It was Mellonis j>roposition, that 
the body which allows radiant heat to pass through it freely 
should be dis-tinguished as diathermic, from the Greek words, 
cto, through (in the same way as we use the term dio. in 
diameter), and BepyLoq, icarmth. or heat : — ^that a body which is 
opaque to heat should be called consequently adiothermic, fit)m a 
priv. and hadepfxiKog, transcolescent, destitute of calorific trans- 
parency. Coloured rays, possessing a different heat-character, 
are called, upon the same principle, thermochroic, that is coloured 
for heat*. Xow, adopting a nomenclature of this order, which 
may be indicative of oiu' scientific results, we should speak of a piece 
of yellow glass which does not allow the chemical rays to pass as 
an o/J.iactinic body, or a body opaque to the actinic or chemical 
rays ; then we may speak of a piece of blue glass as being diactinic. 
The correct mode of expression woiild be to say dia-actinic. but 
it will be more convenient, and possibly allowable, for us to dix)p 
one a, and use the expression diactinic. Then we might, on the 
same principle, use, when speaking of the combined influence of 
colour and actinism, the term actinochrosis. from olktiv, a ray, 
and \poa, colo^j.r, signifying '• o^loured for actinism." In future, 
therefore, instead of asking for an achromatic lens, meaning a 
lens destitute of colour transparency, we should ask for a diactinic 
lens, meaning one which is transparent to the chemical rays. 
I am quite satisfied that until we disassociate from our minds 

* Scientific Memoirs, vol. iii., p. 535. 


the idea that we are dealing with the luminous princij^le of the 
svinshine in the production of om- pictm-es, we shall not arrive 
at that perfection in Photography which it is desii'able we 
should obtain. We certainly shall not succeed in representing 
nature as natiu'e presents herself to ovir eye, until we careftJly 
examine all the phenomena which are involved. We desire to 
produce images equal to those beautifid ones whicli are impressed 
by the physical radiations upon the human retina, and to do this 
we must arrive at the same conditions in oiu' dark chamber, as 
those which obtain in the visual camera obscura of the eye, 
which is not strictly achromatic. 

We commonly hear of a lens being slow or quick ; this is 
purely accidental, arising entirely from the uncertainty in which 
all our optical instrument-makers remain as to the relation of 
the chemical and luminous forces to each other. 

If the lenticular correction does not extend to the point of 
bringing the rays beyond the violet, upon the field of vision, the 
lens will be slow in action, because the light rays interfere, as 
is explained in a previous page ; but if it is ti-uly diactinic it 
will be a quick lens. 

For portraitm-e, and all purposes requiring great distinctness 
of outUne and rapidity of operation, two achromatic lenses are 
usually employed. By this arrangement the focal distance is 
diminished ; the image is much reduced in size, but then it is 
concenti-ated in every respect, and hence improved in all the 
necessary particulars. These lenses are, however, still open to 
the objection that they produce some distortion, which is only 
to be avoided by greatly reducing the size of the apertm^e 
through which the light falls on the lens, and this necessarily 
involves increased sensibility in the preparations we employ. 
The distortion is not to the extent which has been represented, 
but it may, by careful examination, be discovered in the finest 
photographic portraits to a greater or less extent. 





It is natural to suppose, that a process which involves the most 
delicate chemical changes requires more than ordinaiy cai-e in 
the selection of the substance upon which preparations of a pho- 
tographic character are to be spread. Tliis becomes the more 
evident as we proceed in oiu* experiments to produce increased 
conditions of sensitiveness. As the material, whatever it may be, 
is rendered more susceptible of change under solar influence, the 
gTeater is the difficulty of producing pei-fectly uniform sui-faces, 
and with paper this is more particularly experienced than with 
either metal or glass plates. Paper is, however, so convenient 
and so economical, that it is of the first importance to ovei'come 
the difficulties which stand in the way of its use, as the tablet 
on which the photogTaphic picture is to be delineated. 

The principal difficulty we have to contend with in using paper 
is, the diflTerent rates of imbibition which we often meet with in 
different pai'ts of the same sheet, arising from trifling inequalities 
in its textm-e and rmequal sizing. This is, to a certain extent, 
to be overcome by a very careful examination of each sheet by 


the light of a lamp or candle at night. By extending the paper 
between the light and the eye, and slowly moving it ujd and 
down, and from left to right, the variations in its textiu-e will be 
seen by the diflerent quantities of light which permeate it ; and 
it is always the safest course to reject every sheet in which any 
inequalities are detected. By day it is mure difficult to do tliis 
than at night, owing to the interference of the reflected with the 
transmitted light. It will, however, often happen that paper 
which has been carefully selected by the above means will imbibe 
fluids unequally. In all cases where the pa^Der is to be soaked 
in saline solutions, we have another method of discovering those 
sources of annoyance. Having the solution in a broad shallow 
vessel, extend the paper, and gradually ch-aw it over the surface 
of the fluid, taking care that it is wetted on one side only. A 
few trials will render this perfectly easy. As the fluid is absorbed, 
any irregularities are detected by the difierence of appearance 
exhibited on the upper part, which will, over well-defined spaces, 
remain of a dull-white, whilst other portions will be shining vdth 
a reflective film of moisture. Where the importance of the use 
to which the paper is to be applied, — as, for instance, to copying 
an elaborate piece of architecture, or for receiving the portrait 
of an individual — will repay a little extra attention, it is recom- 
mended that the paper be tried by this test with ^^ure water, 
and dried, before it is submitted to the salting operation. It 
will be sometimes found that the paper contains minute fibres of 
thread, arising from the mass of which it is formed not having 
been reduced to a perfect pulp. Such paper should be rejected, 
and so also should those kinds which are found to have many 
brown or black specks, as they materially interfere with some 
of the processes. Many of the spots in j^aper are formed by 
particles of brass wu-e which have separated from the machinery 
employed in its manufactiu-e, or they may be fragments of buttons 
derived from the rags, and minutely divided in pulping. Some 
specimens of paper have an artificial substance given to them by 
sulphate of lime (plaster of Paris) ; but, as these are generally 
the cheaper kinds of demy, they are to be avoided by purchasing 
the better sorts. The plaster can be detected by fusing a sheet 
of the paper and examining the quantity of ash. Pure paj)er 
leaves less than I per cent, of ash. If plaster is present the ash 
wUl be much more considerable : the increase of weight is, how- 
ever, sometimes due to kaoHn. No really sensitive photographic 
paper can be prejjared when sulphate of lime is jiresent ; and it 
has the singular property of reversing the action of the Iodides 
on the darkened chloride of silver, producing a negative in the 
place of a positive photograph. It is the custom for paper-makers 


to fix their names and the date on one leaf of the sheet of writing 
paper. It is wise to reject this leaf", or to select paper which is 
not so marked, as in many of the photographic processes which 
will be described, these marks are brought out in most annoying 
distinctness. From the vax'ious kinds of size which the manu- 
facturers use ui theu' papers, it wall be found that constantly 
varying effects wtII arise. A well-sized paper is by no means 
objectionable ; on the contrary, organic" combinations exalt the 
darkening property of the nitrate and chloride of silver. But 
unless we are careful always to use the same variety of paper 
for the same purpose, we shall be much perplexed by the con- 
stantly varying results which w^e shall obtain. No doubt, with 
the advancing importance of the art, the demand for paper for 
photographic pui-poses wdll increase ; manufactiu-ei-s will then 
find it worth the necessary care to prejDare paper agreeably to 
the directions of scientific men. Several of our paper-makers 
are now paying much attention to the preparation of photo- 
graphic jiaj^er, and are considerabl}' improA-ing it. I have been 
most obligingly furnished by Mr. Sandford, of Paternoster Row, 
with specimens of a great variety of Foreign and English papers, 
and from the care that gentleman is bestowing on this subject, 
the most important advantages may be expected. All who desire 
to make any progTess in photogi-aphy must take the necessary 
precautions, or be content to meet ^vith repeated failures. 

The photographic peculiarities of paper mainly depend upon 
the sizes employed. The English paper manufacturers very 
commonly employ gelatine, and this in very different conditions. 
The French, on the contrary, use starch, and this, from the strong 
aflinity existing between stai'ch and iodine, appears to be one 
reason why the French paper is superior for the calotype in some 
of its modifications. 

Resin soap is largely employed as a size. The soap is applied 
to the bibulous papei', and then decomposed by an acid w^ater, 
leaving a fine film of resia spread upon the sui'face, susceptible 
of the highest polish. 

The following tables wall exhibit the results of an extensive 
series of experiments, which were undertaken after the publica- 
tion of Sir J. Herschel's memoir, On the Chemical Action of tlve 
Rays of the Solar Spectrum, in which he has given a table of 
results, obtained Avith different preparations on various kinds of 
paper ; but as he has not established the influence of the paper, 
except in a few instances, independent of the preparation, it be- 
came desirable to do so ; and the residt of several years' ex- 
perience has proved the correctness of the conclusions then 
arrived at. 


In pursuing this inquiry, it was found that the same descrip- 
tion of paper, from different manufacturers, gave rise to widely 
different effects ; so that the most carefu.lly conducted experi- 
ments, several times repeated, have only given approximations 
to the truth. The foi"m of experiment was to select a number 
of specimens of paper, — prepare them with great care in precisely 
the same mannei', and expose them to the same solar influences. 
They were partly covered with a piece of coloiu-less glass,^the 
object of this being to determine whether under it the action 
was quicker or slower than when exposed uncovered. Sii- John 
Herschel has shown that there are some peculiar differences in 
this respect ; and this method offered a very correct mode of 
determining the relative effects. 

I. — Papers prepared v-ith Chloride of Sodium and Nitrate of 


a. Supei-fine satin post Considerable exalting effect. 

h. Thick wove post Depressing influence. 

c. Superfine demy Slight exalting effect. 

d. Bath di'awing card Changes slowly. 

e. Thick post Slight exalting effect. 

f. Common bank post Ditto. 

g. Thin post Very tardy. 

h. Tissue paper Considerable exalting effect. 

II. — Papers prepared loith Chloride of Barium and Nitrate of 


a. Superfine satin post Slight exalting influence. 

h. Thick wove post Ditto, but stronger. 

c. Superfine demy Similar to a. 

d. Bath tli-awing card Similar to a. 

e. Thick post Considerable exalting influence. 

f. Common bank post Similar to a. 

(/. Thin post Similar to e. 

h. Tissue paper Results uncertain. 

III. — Papers prepared with Muriate of Ammonia and Nitrate 
of Silver. 

a. Superfine satin post Strong exalting influence. 

h. Thick wove post Results uncertain — dependent on 

the size employed. 

c. Superfine demy Slight exalting effect. 

d. Bath di'awing card. Results uncertain. 


e. Thick post Results uncertain. 

f. Common bank post Very slow. 

g. Thin post Ditto. 

h. Tissue paper Strong exalting influence. 

IV. — Papers prepared with Iodide or Bromide of Potassium and 
Nitrate of Silver.. 

a. Superfine satin post Darkens slowly. 

h. Thick wove post Results uneei-tain. 

c. Superfine Demy Strong exalting influence. 

d. Bath Di-awing card Very slowly changes. 

e. Thick post Depressing influence. 

f Common bank post Slight exalting efiect. 

g. Thin post, Ditto. 

h. Tissue paper Results imcertain. 

Unsized paper has been recommended by some, but in no in- 
stance have I found it to answer so well as paper which has been 
sized. The principal thing to be attended to in preparing sensi- 
tive sheets — accoi'ding to my experience, extended over a period 
of ten years, although it is opposed to the views of some yoimg 
but able photogi'aphers — is to prevent, as far as it is possible, the 
absorption of the solutions into the body of the paper — the 
materials should be retained as mxich as possible vipon the very 
surface. Therefore the superficial roughness of unsized sheets, 
and the depth of the imbibitions, are serious objections to their 
use. It must not, however, be forgotten, that these objections 
apply in their force only to the silver preparations ; in some 
modifications of the processes, with the bichromate of potash, 
the common bibulous paper, used for filtering liquids, has been 
fovmd to answer remarkably well, on account of the facility with 
which it absorbs any size or varnish. 

Great annoyance often ai'ises fi-om the rapid discoloiiration of 
the more sensitive kinds of photographic cU'awing paper, inde- 
pendent of the action of light, which appears to arise from the 
action of the nitrate of silver on the organic matters of the size. 
Unsized paper is less liable to this change. If we spread a pm*e 
chloiide of silver over the papei*, it may be kept for any length 
of time without any change of its whiteness taking place in the 
dark. Wash it over with a solution of nitrate of silver, and, 
particularly if the paper is much sized, a very rapid change of 
colotu" will take place, however carefully we may screen it from 
the light. From this it is evident that the oraranic matter of 


the size is the principal cause of the spontaneous darkening of 
photographic papers prepared Math the salts of silver. 

The most curious part of the whole matter, is, that in many 
cases this change is earned on to such an extent that a revival 
of metallic silver takes place, to all appearance in opposition to 
the force of affinity. This is very difficult to deal with. I can 
only view it in this light — the nitric acid liberates a quantity of 
carbonaceous matter from the paper, which, acting by a function 
peculiarly its own, will at certain temperatures effect the revival 
of gold and silver, as proved by Count Rumford's experiments. 

Having been informed that the paper-makei-s are in the habit 
of bleaching their papers with svdphui- and suli^hites, I have sub- 
mitted a considerable quantity of the browned papers to carefid 
examination. lu all cases where the paper, covered with chloride 
of silver, has suddenly hlackened, I have detected the presence 
of suljihm-. Consequently, when the darkening goes on rapidly, 
and terminates in blackness, we may, I think, correctly attribute 
it to the fonnation of a sulphuret of silver. 

It is, however, certain that the slow action of organic matter 
is sufficient, under certain cu'cumstances, to set uji a chemical 
change, which, once started, piogresses slowly, but certainly, 
until the compound is reduced to its most simple form. 

China clay — kaolin — has of late years been much used by the 
paper manufactiu-ers, for the double piu-pose of giving weight to 
the paper, and of enabling them to produce a smooth surface 
upon all the finer varieties of paper ; such as the enamelled satin 
post. This compound of alumina and silica would not, if the 
finest varieties of clay were employed, be likely to do much mis- 
chief in the papers used for photography; but the less pure 
varieties of the Cornish gIaj are employed, and this commonly 
contains the oxides of iron and other metals in a state of very 
fine division; and these, where they come to the surface, form 
little centres of action, from which dark cu'cles spread in rather 
a curious manner. Thin papers have been tried, and many 
varieties would answer exceedingly well, but that nearly all 
kinds are found penetrated with small holes, which, though of 
minute dimensions, suffer light to pass freely, and consequently 
produce a spottiness on the resulting picture. Sir John Hei"schel 
found that this eAol could be remedied by fastening two pieces 
of such paper together; but this method is troublesome and un- 

Retiu-ning to the consideration of size in the paj^er, the above- 
named authority — who employed the lead salts in some of his 
photograpliic processes — has the follo^^-ing remarks : — 

■' The paper with a basis of lead turns yeUow by keeping in 


the dark, and the tint goes on gradually deepening to a dark 
brown. But what is very singular, this change is not equally 
rapid upon all kinds of paper — a difference depending, no doubt, 
on the size employed; wliich, it may be observed here once for 
all, is of the utmost influence in all photographic processes. In one 
sort of paper (knowTi by the name of blue tvove ]}ost) it is instan- 
taneous, taking place the moment the nitrate (if abundant) is 
applied. And yet I find this paper to resist discoloiu'ation, by 
keeping, better than any other, when the mordant base is silver 
instead of lead. On the other hand, a paper of that kind called 
smooth demy, rendered sensitive by a combination of lead and 
silver, was found to acquire, by long keeping, a lead or slate 
colour, which increases to such a degree as might be supposed to 
render it useless. Yet, in this state, when it is impressed with 
a photographic image, the process of fixing with hyposrdphite of 
soda destroys this colour completely, leaving the gi-ound as white 
as when fii'st prepared. This fortimate restoration, however, 
does not take place when the paper has been browned as above 
described. Some of the muriatic salts also are more apt to 
induce this discolouration than others, especially those with the 
earthy bases." 

It will be evident from these remarks that it is of the utmost 
importance to secure a paper which shall be as chemically piire 
as possible. Experience has proved that recently-manufactui-ed 
paper does not answer equally well with that which has been 
made for a year or two. It has been thought by many that this 
was an unfounded statement, but it is not so ; and the causes 
operating to the improvement of paper by age are evident. The 
organic matter of the size is liable to a spontaneous change : 
this goes on for a considerable time, but at length the process 
becomes so exceedingly slow that it may, for all pi-actical pur- 
poses, be said vii-tually to rest. Paper changes its colour by 
keeping from this cause, and I have found that such as I have 
selected from the shop-ivorn stocks of stationers has been generally 
superior to that which has been more recently manufactured. 

Select, therefore, paper of a uniform textiu-e, free from spots, 
and of equal transparency, choosing the oldest rather than the 
newest varieties. 

Where the process is highly sensitive for which the paper is 
desired, it is important to treat it in the following manner : — 
Ha\Tng a shallow dish sufficiently large to receive the sheets of 
paper without in any way ci-umpling them, it is to be filled with 
A-ery clear filtered water, to wliich a sufficient quantity of nitric 
acid has been added to make it slightly som- to the taste. Taking 
a sheet of paper, it should be laid on a porcelain slab, and sponged 


with clean water on both sides, after which it should l^e placed 
in the acidulated water, and allowed to remain in it for several 
hours. Too many sheets should not be placed in the vessel at 
the same time. After a time they should be removed in mass, 
placed on the slab, and left for half an hour under gently flowing 
water, — this removes all the acid, and all those metallic and 
earthy matters which it has removed fi-om the paper. After 
this it is to be dided, and it is then fit for photographic use. 

Tliis chapter has been deemed unnecessarily long; but, upon 
renewing many of the experiments, I have become so convinced 
of its importance in all particulars, that I could not induce my- 
self to curtail it. All who aim at excellence in photography 
should repeat the experiments and closely observe the results. 



The most simple method of obtaining sim-pictures, is that of 
placing the object to be coj^ied on a sheet of prepared paper, 
pressing it close by a piece of glass, and exposing the arrange- 
ment to sunshine; all the parts exposed darken, "while those 
covered are protected fi-om change, the resulting pietui-e being 
ivhite upon a darh ground. 

It sho\ild be here stated, once for aU, that such pictures, how- 
soever obtained, are called negative photograjplis ; and those 
which have their lights and shadows correct as in nature — dark 
upon a light ground, ?ccq jiositive photographs. 

The accompanying woodcut. Fig. 36, represents a negative 
copy of a cun-ant leaf, and Fig. 37, the positive copy obtained 
from it. 

If a cojiy is made by means of the camera, of any illuminated 
object, the picture being produced by the darkening of a white 



or yellow paper, it will be evident that the highest lights will be 
represented as dark portions, and the shadows as lights. Thus 
we obtain a negative image. The female figure in the adjoining 
woodcut, Fig. 38, is copied from a calotype negative portrait ; and 
this negative being used by superposition on another prepared 
piece of paper, produces a positive in which the lights and shades 
are natural, as in the second figure, Fig. 39. 

Let us commence by supposing the experimentalist to be sup- 
plied with paper prepared by some one acquainted with the 
manipulation, and that he is now to observe for the first time 
the effects produced. 

For the production of photographic drawings, it is necessary 
to be provided with a copying frame and glass, the most conve- 
nient size for which, is something larger than a single leaf of 
quarto post wi'iting paper. The glass must be of such a thick- 
ness as to resist some considerable pressure, and it should be 
selected as colourless as possible, great care being taken to avoid 


such glasses as have a tint of yellow or red, these colours pre- 
venting the permeation of a large proportion of the most effi- 
cient rays. Figures 40 and 41 represent such a frame in its most 
simple form ; the fii'st showing it in front, as it is employed in 
taking a copy of leaves, and the other the back, with its piece 
of stout tinned iron, or board, which presses on a cushion, secur- 
ing the close contact of the paper with every part of the ob- 
ject to be copied, and its bi"ass bar, which, when pressed into 
angular apertm-es in the sides of the frame, gives the required 
pressiu'e to the paper. To copy leaves we proceed thus : — 

Having placed the frame face downwards, carefully lay out on 
the glass, the object to be copied, on which place the photo- 
gi'aphic paper veiy smoothly. 
Then cover this with the cushion, 
which may be either of flannel 
or velvet, fix the metal back, 
and adjust it by the bar, until 
every part of the object and 
paper are in the closest contact. 
For all ordinary uses, this frame 
answers exceedingly well ; but a 
more convenient pressure frame 
is constructed in the manner 
represented by Fig. 42. This ^^ 

contains two bars, one of them 

movable, and both of them may be fixed in any required posi- 
tion by binding screws. 

In arranging botanical specimens, the imder sm-face of the 
leaves should be next the glass, their upper and smooth siu-face , 
in contact with the paper. Although very beautiful copies may 
be taken of di-ied specimens, they bear no comparison with those 
from fresh-gathered leaves or recently collected plants, of which, 
with the most delicate gradations of shades, the veins of the 


leaves, and the do-rni clothing the stems, are exhibited with in- 
comparable fidelity. In the event of the j^lant ha'V'ing any thick 
roots or buds, it vriH be best to divide them with a sharp knife, 
for the pui-pose of equalizing the thickness in all parts, and in- 
suring close contact. 

Eugl'a^■ings are to be placed with theii' faces to the prepared 
side of the photographic paper, laid veiy smoothly on the 
glass, and then ■s'sith the cushion aud back pressed into the 
closest contact possible : the least difference in the contact, by 
peiTuitting dispersion, occasions a cloudiness and want of sharp- 
ness in the photograph. 

Of coiu-se a co-pj of anything taken by means of the i-ays 
which have passed through it, must present all the defects as 
well as all the beauties of the article, whatever it may be. 
Thus, in copying a print, we have, besides the lines of the en- 
graving, all the imperfections of the paper : This renders it 
necessary that those engi'avings should be selected which are 
on tolerably perfect paper. If the preservation of the engi-aving 
is not a matter of much moment, by washing it over the back 
with a vaiTush of Canada balsam and spuits of turpentine, it is 
rendered highly transparent, and the residting impression is 
ranch improved. Cai-e must, however, be taken to use the var- 
nish very thin, that it may not impart any yellow tinge to the 
paper. An exposiu-e of a few minutes only is sufficient to 
produce strong aud faithful copies dui'ing sunshine ; but in dif- 
fused daylight a longer period is necessaiy. 

Some kind of copying fi-ame is an indispensable requisite to 
the photographer: it is used for copying all objects by trans- 
mission, and for multiplying the original pictures obtained by 
means of the camera obscura from nature : it is, indeed, the 
printing-press of the artist. Some prefer two plates of stout 
plate-glass pressed very closely together with clamps and screws ; 
but, as the intention is to bring the object to be copied and the 
sensitive paper into the closest jDossible contact, niimerous me- 
chanical contrivances will suggest themselves for this purpose to 
the ingenious. 

A great niunber of experiments should be made with the 
copying frame before there is any attempt at using the camera 

The Camera Obscm-a, or Dark Chamber, was the invention of 
Baptista Poiia, of Padua. Its piinciple will be best under- 
stood by the very simple experiment of darkening a room by 
closing the window-shutters and admitting a pencil of light 
thi'ough a small hole in them. If a piece of paper is held at a 
little distance from this hole, the figui-es of external objects will 


be seen delineated upon it ; and, by putting a small lens orer the 
bole, they are rendered much more evident, from the condenisa- 
tion of the rays by the spherical glass. 

If, instead of a darkened room, we substitute a darkened box 
(Fig. 43), the same effect will be seen. Suppose, in the first 
place, the box to be without the lens, the rays would pass from 
the external aiTOw in nearly right lines thi'ongh the opening, 
refracted only in passing the solid edges of the hole, and foiTu 
an image on the back of the dark box. The lens refracts the 
rays still more, and a smaller, but a more perfectly defined pic- 
tiu'e, is the result. 

As in the phenomena of ^-ision, so in the camera obscura, the 
image is produced by the radiations proceeding from the external 
object; and as these radiations progress from Tai'ious parts, more 
or less illuminated, so are the high lights, the middle tints and 
shadows, most beautifully preserved in the lenticular image. 
The colours, also, being in the fii"st instance the effect of some 
physical modification of the primary cause, are repeated under 
the same influence ; and the definition, the coloiu", and soft gra- 
dation of light and shadow, are so perfect, that few more beauti- 
ful optical effects can be exhibited than those of the camera obscvira. 

Now as every ray of light producing the coloured image is 
accompanied by the chemical principle actinism, and as this is 
regulated in action by the luminous intensity of the rays, the 
most luminous (j/ellow) producing the least chemical effect, while 
this increases with the diminishing illuminating power of the 
coloured rays of the radiating source, we have the impression 
often opposed, in its relations of light and shade, to the colom-s 
of the object we would copy. By referring to the fi-ontispiece 
to the present volume, the effects produced by copying a coloured 
image will be seen. The yellows, reds, and those colours usually 
regarded as lights, are copied as shadows : hence the importance 
of attention to the coloui-s of the di-ess, when a porti-ait is to be 
taken by any photographic process. 



In the ordinary cameras used by artists for sketching, a mir- 
ror is introduced, wliich throws the image on a semitransparent 

Fig. 44 is a section of one form of such an instimment : a a 
represents the box, in one end of which is fixed the lens b. 
The lenticular image falls on the mir ror c, placed at such an 
angle that it is reflected on the plate of ground-glass d. e is 
a screen to prevent the overpowering influence of daylight, 
which would render the picture almost invisible. This form of 
the apparatus, though very interesting as a philosophical toy, and 

extremely useful to 
the artist, is by no 
means fitted for pho- 
togi'ajihic purposes. 
The radiations from 
external obj ects sufier 
considerable diminu- 
tion of chemical power 
in penetrating the 
lens, and the reflec- 
tion from the mirror 


SO far reduces its in- 
tensity, that its action on photographic agents is slow. To obviate 
the objection of the reflected image, it is only necessary to place 
the photographic paper in the place of the mirror, but not in an 
angular position. 

A great variety of these instruments have been introduced to 
the notice of students of the art, many of them so unnecessarily 

expensive that they are beyond the reach of the humble amateur. 
It is conceived that a few examples of mechanical contrivances 
by which the instrument is rendered portable, and in all respects 
convenient will not be out of place. Fig. 4-5 represents one box 
sliding within the other for the purpose of adjusting the focus, 
the lens being fitted into a brass tube, which screws into the 
front of the camera. The woodcut (Fig. 46) is but one box. 


the lens being fitted into one brass tube sliding in anotber, like 
a telescope tube, the movable part being adjusted by a screw 
and rack. The mouth of the tube is contracted, 
bj which any adventitious radiations are ob- 
structed, and a brass shade is adjusted to close 
the opening if requii-ed ; the paper is placed 
in a case fitted with a glass fi-ont, as in Fig. 47, 
and a shutter, by which it is protected from 
the light until the moment it is required to 
throw the image upon it. 

In the fii'st edition of this work, a form of 
camera was described, which possesses the ad- 
vantages of extreme cheapness, and of being in 
most respects convenient. It is, therefore, here 
described in the language I employed in 1841 : — *7. 

A photographic lens should possess, according to Sir John 
Herschel, "the three qualities of a flat field, a sharp focus at great 
inclinations of the visual ray, and a perfect achromaticity." There 
can be no doubt but these qualifications are very essential, — 
the two fii-st particularly are indispensable, and there is but one 
objection to the latter. We can only produce perfect achroma- 
ticity by a combination of glasses, and experiments prove that 
by increasing the thickness of the object-glass, *and the number 
of reflecting and refracting surfaces, we intennipt a considerable 
portion of actinism, and consequently weaken the action on the 
photographic material, whatever it may be; but ovir opticians 
have succeeded to a great extent in overcoming this ditficulty. 
We may, to a considerable degree, get rid of the defects arising 
from chi-omatic dispersion, without having recourse to a combi- 
nation of glasses of difiereut refracting powers. I long used my- 


self, and constructed for others, a camera obscura which answered 
well, with a non-acliromatic lens. Fig. 48 a represents the aper- 

* The recent experiments of the Eev. Mr. Stokes most fully confirm this view. 



ture of tlie lens ; i i', a box sliding into an outer case, h h' ; k k, 
a third division, containing a ground glass at the back, and a 
door which caai be raised or lowered by the screw g, the whole 
fitting into the frame h h'. 

Figui-e 49 is a section of the camera, a is a lens of a perisco- 
pic form, whose radii of cui'vature are in the proportion of 2 to 1. 


This meniscus is placed with its convex surface towards the 
plane of representation, and with its concavity towards the 

The apertui-e of the lens itself is made large, but the pencil 
of rays admitted is limited by a diaphragm, or stop, constructed 
as in the figure at b, between it and the plane of representation, 
at about one-tenth of the focal length from the lens. By this 
arrangement objects are represented with considerable distinct- 
ness over every part of the field, but little 
difterence being observable between the 
edges and the centre, c is the plate of 
ground glass at the back, which serves to 
adjust the focus by, and also to lay the 
photographic paper on, when we desire to 
copy any object; d, a door to shut off the 
light from the paper or plate until the 
moment we desii-e to expose it to luminous 
agency. Fig. 50 represents this screen or 
jS door more perfectly, in the act of falling; 
e is a d,oor at the back, through which the 
picture formed on the opaque glass is examined ;y5 a pin, keeping 
the door, d, in its place. 

The following figures (Figs. 51, 52, 53) represent a more per- 
fect arrangement. Its conveniences are those of folding, and 
thus packing into a very small compass, for the convenience of 



travellers. It is, however, only adapted for views, and not for 

With the camera obsciu-a properly arranged, and the copying 
frame, the photogi'aphic student who confines his attention to 
the processes on paper 
has nearly all he re- 
quires. For the con- 
venience of adjusting 
the instrument to dif- 
ferent heights, and to 
different angles of ele- 
vation, tripod stands 
are convenient, but 
not altogether indis- 
pensable. They are 
made in several ways; 

the two figures, 54 and 55, representing those which appear 
best adapted to the use of the traveller. The arrangement of 
compound legs shown in Fig. 54 insxu-es greater steadiness than 
the other ; but the range of movement in Fig. 55 gives it some 

Beyond these things, a few dishes, such as are represented in 
Fig. 56, A A ; and a feme b, upon which a photograph can be 
placed for the jKirpose of being washed, are the only things 
required for the practice of photography, except those pieces of 
apparatus which, belonging to special processes, "wdll be found 
described in the chapters devoted to them. The object has been 
in this chapter to enumerate those only which are necessary for 
an amateiu" to make his rudimentary experiments. 

My object in describing tliis camera is to enable the yoimg 
photographer to pui^ue his earlier studies, without ha-viug to in- 
cur the cost of a perfect lens. An inferior, and consequently 



low-priced ackromatic lens, slioiild ever be avoided, tlie results 
with sucli being far less perfect than those obtained by means of 
a good periscopic lens. 



The only apparatus required by the pliotogi'aphic ai-tist for the 
prepai-ation of his papers, are — some veiy soft sponge brushes 
and Jarge camel haii' pencils (no metal should be employed in 
moimting the brushes, as it decomposes the silver salts), a wide 
shallow vessel capable of receiving the sheet without folds, a 
few smooth planed boards, sufficiently large to stretch the paper 
upon, and a porcelain or glass slab. He must supply himself 
with a quantity of good white blotting-paper, and several pieces 
of soft linen or cotton cloth ; a box of pins ; a glass rod or two ; 
some porcelain capsides; and some beaker glasses, graduated 
measui-es, scales, and weights. 

Section I. — Xitr.\te of Silver. 

The most simple kind of photographic paper which is pre- 
pared with the silver salts is that washed with the niti-ate of 
silver only; and for many purposes it answers well, particularly 
for copying lace or feathers ; and it has this advantage over 
every other kind, that it is perfectly fixed by well soaking in 
warm water, free from chloride of sodiiim. 

The best proportions in which this salt can be used are 60 grs. 
of it dissolved in a fluid ounce of distilled water. Care must be 
taken to apply it equally, with a quick but steady motion over 
every part, of the paper. It will be found the best practice to pin 
the sheet by its four cornel's to one of the flat boards above-men- 
tioned, and then, holding it with the left hand a little inclined, to 
sweep the bnish, from the upper outside corner, over the ■\^•hole of 
the sheet, remo^'ing it as seldom as possible. The lines in fig. 51 
will represent the manner in which the brash should be moved 
over the paper, commencing at a and ending at h. On no ac- 
count must the lines be brushed across, nor must we attempt to 




cover a spot wliicli has not been ■wetted, by the application of 
fresh solution to the place, as it "will, in darkening, become a 
well defined space of a different shade from 
the rest of the sheet. The only plan is, 
"when a space has escaped our attention in 
the fii'st washing, to go over the whole 
sheet "with a more dilute solution. It is, 
indeed, always the safest com'se to give the 
sheet two washings. 

The nitrated paper not being very sen- 
sitive to luminous agency, it is desu'able to 
increase its po"wer. This may be done to 
some extent by simple methods. 

By soaking the paper in a solution of 
isinglass or parchment size, or by rubbing it over with the white 
of egg, and diying it prior to the application of the sensitive 
"wash, it will be found to blacken much more readily, and assume 
different tones of colom*, "which may be varied at the taste of the 

By dissolving the nitrate of silver in rectified spii-its of "wine, 
instead of water, we produce a tolerably sensitive nitrated j^aper, 
"which darkens to a very beautiful chocolate brown; but this 
"wash must not be used on any sheets prepai'ed "with isinglass, 
parchment, or albiunen, as these substances are coagulated by 
alcohol, and "wash up forming streaks. 

The nitrate of silver is not sufliciently sensitive to change 
readily in difiused light ; consequently it is unfit for use in the 
camera obscura, and it is only in strong sunshine that a copy of 
an engraving can be taken in any moderate time. 

Ammonio-Nitrate of Silver,— This is an exceedingly useful 
preparation for many 23urposes. It is prepared by adding 
ammonia to a solution of nitrate of silver : a deep olive preci- 
pitate of oxide of silver takes place ; more ammonia should then 
be added, di*op by drop, untd this precipitate is redissolved, 
great care being taken that no more ammonia is added than 
is necessary to effect a perfect solution of the oxide of silver. 
This solution is more sensitive than the nitrate, and may be used 
"with advantage for copying by superposition; but it is not fitted 
for the camera obscm^a. 

Section II. — Chloride of Silver. 

This is one of the most important salts employed in photo- 
graphy ; it therefore demands especial attention. 

Muriated Papers, as they are termed, are formed by producing 



a chloride of silver on their surface, by washing the paper with 
the solution of chloride of sodium {muriate of soda), or any other 
chloride, and when the paper is dry, with a solution of nitrate 
of silver. 

It is a very instnictive practice to pi-epare small quantities of 
solutions of common salt and nitrate of silver of difierent strengths, 
to cover slips of paper mth them in various ways, and then to 
expose them altogether to the same radiations. A cui-ious variety 
in the degi-ees of sensibility, and in the intensity of coloui-, will 
be detected, showing the importance of a veiy close attention to 
proportions, and also to the mode of manipulating. 

A knowledge of these preliminary but important points having 
been obtained, the preparation of the paper should be proceeded 
with ; and the following method is recommended : — 

Taking some flat deal boards, perfectly clean, pin upon them, 
by theu' foui- corners, the paper to be prepared ; observing the 
two sides of the paper, and selecting that side to receive the pre- 
paration which presents the hardest and most uniform siu'face. 
Then, dipping one of the sponge brushes into the solution of 
chloride of sodium, a sufficient quantity is taken up by it to 
moisten the siuface of the paper without any hard rubbing; 
and this is to be applied with great regularity. The papers being 
" salted," are allowed to dxy. A great number of these may be 
prepared at a time, and kept in a portfoho for use. To render 
these sensitive, the pajiers being pinned on the boards, or care- 
fully laid upon folds of wliite blotting paper, are to be washed 
over with the nitrate of silvei', applied by means of a camel-haii" 
pencil, obsei-ving the instructions pre\'iously given as to the 
method of moving the brush upon the paper. After the first 
wash is applied, the paper is to be di'ied, and then subjected 
to a second application of the silver solution. Thus prejoared, 
it will be sufficiently sensitive for all piu-poses of copying by 
application. The second wash is applied for the purpose of 
insuring an excess of the nitrate of silver in combination, or, 
more properly speaking, 
mixed with the chloride. 
Mr. Cooper, with a view 
to the production of a uni- 
form paper, recommends 
that it be soaked for a con- 
siderable length of time in 
the saline wash, and, after "^ 
it is ch-ied, that the sheet ss 

should be dipped into the silver solution ; while the opei-ator 
moves over its siu'face a glass rod held in two bent pieces of glass. 




as in fig. 58 j the object of "^liicli is to remove the small air- 
bubbles forming on the sui-face of the paper, -n-hich protect it 
fix>m the action of the fluid. This process, however ■well it may 
answer in preparing p>aper for copying engravings, ■vrUl not yield 
paper sufficiently sensitive for camera purposes; and it is objec- 
tionable on the score of economy, as a larger quantity of the silver 
solution is required to decomjx)se the cominon salt than in the 
process previously described. 

The young photographer -svould find it interesting to study the 
more striking pectdiarities of a few of the preliminary washes, 
such, indeed, as those noticed in the scientific division. It will 
be found that nearly every variety of paper exj)Osed to the fiill 
action of the solar beams will pass through varioas shades of 
brown, and become at last of a deep olive colour : it must there- 
fore be tmderstood that the process of darkening is in all cases 
stopped short of this point. Remembering this, it will be found 
that very peculiar and often beautiful tints are produced by the 
chloride of barium, the hydro-chloride of ammonia, and some 
of the organic acids. 

Papei-s prepared with the chloride of sodium have, however, 
been more extensively used than any others for positive pic- 
tures, owing to the ease with which this material is always to be 
procured ; and for most purposes it answers as well as any other, 
but it does not produce the most sensitive photographic .siu-face. 

The proportions in which this salt has been used are exceed- 
ingly various ; in general, the solutions have been made too strong ; 
but several chemists have recommended washes that are as much 
too weak. For different uses, solutions of various qualities should 
be employed. It will be found well in practice to keep papers 
of three orders of sensitiveness prepared : the proportions of salt 
and silver for each being as f jllows : — 

A paper may be prepared vrith. the chloride as follows : — 

Chloride of sodium, thirty graius to an ounce of water. 

!Mitrate of silver, one hundred and twenty grains to an ounce 
of distilled water. 

The paper is first soaked in the saline solution, and after being 
carefully pressed between folds of blotting paper and dried, it is 
to be w^ashed twice with the solution of silver, drying it by a 
warm fire between each washing. This paper is very liable to 
become brown in the dark. Although images may be obtained 
in the camera on this paper by about half an hour's exposure, 
they are never very distinct., and may be regarded as rather 
curious than useftiL 

A less sensitive paper for copies of engravings — botanical or 
entomological sj^ecimens, should have the following proportion : — 


Cliloride of sodium, t'.venty-five gi-ains to an ounce of water. 

Nitrate of silver, ninty-nine grains to an ounce of distilled 

And a jet more common sensitive paper, for copying lace- 
work, feathers, patterns of watch-work, &c., may be thus pre- 
pared at less expense : — 

Chloride of .sodium, twenty grains to an ounce of water. 

Nitrate of .silver, sixty grains to an ounce of distilled water. 
Applied as above directed. 

This paper keeps tolerably well, and, if carefiilly prepared, 
may always be depended upon for darkening equally. 

Section III. — Iodide of Silver. 

This salt was employed very early by Talbot, Herschel, and 
others, and it enters as the principal agent into Mr. Talbot's 
calotype process. Paper is washed with a solution of the 
iodide of potassium, and then with nitrate of silver. By this 
means papers may be prepared which are very sensitive to 
himinous influence, provided the right proportions are hit ; 
but, at the same time, nothing can be more insensible to the 
same agency than the pure iodide of silver. A singular dif- 
ference in precipitates to all appearance the same, .led to the 
belief that more than one definite compound of iodine and silver 
existed ; but it is now proved that pure iodide of silver will not 
change colour in the sunshine, and that the quantity of nitrate 
of silver in excess regulates the degree of sensibility. Experi- 
ment has shown that the blackening of one variety of iodidated 
paper, and the preservation of another, depends on the simple 
admixture of a very minute exce.s.s of the nitrate of silver. The 
papers prepared with the iodide of silver have all the peculiari- 
ties of those prepared with the chloride, and although, in some 
in.stance.s, they seem to exhibit a much higher order of sensi- 
tiveness, they cannot be recommended for general purposes 
with that confidence which experience has given to the chloride. 
It may, however, be proper to state the best proportions in 
which the iodidated papers can be prepared, and the most 
approved method of applying the solutions. 

The fijiest kind of paper being chosen, it should be pinned by 
its four comers to a board, and carefully washed over with a 
solution of six grains of the nitrate of silver to half an oimce of 
water : when this is dry, it is to be wa.shed with a solution of 
iodide of potassium, five grains in the same quantity of water, 
and di'ied by, but at some little distance from, the fire j then, 


some short period before the paper is required for use, it must 
be again washed with the silver solution, and quickly dried, with 
the same precaution as before. If this paper is warmed too 
mvich in drying, it changes from its delicate primrose colour to 
a bright pink or a rosy brown, which, although still sensitive to 
solar influences, is not so readily changed as when in an unaltered 
state. The peculiar property of this salt to change thus readily 
by calorific influence, and some other very remarkable efiects 
produced on already darkened paper when washed with a 
salt of iodine, and exposed to artificial heat, or the pure calorific 
rays of the spectrum, appears to promise a process of drawing of 
a new and peculiar character. 

The few simple directions here given will be sufficient to 
guide the young experimentalist in his earliest essays ; and it 
is particidarly recommended that the first experiments shovdd 
be confined to the salts named in this chapter. The minute 
details requii'ed for the more highly sensitive processes are 
described in immediate connection with the process to which 
they refer. 

I woidd advise the amateur to start upon his studies with 
but three solutions — 1st, Chloride of sodium ; 2d, Nitrate of 
silver ; 3d, Hyposulphite of soda. With the first he carefully 
washes several sheets of good letter paper on one side only, and 
dries ; with the second he, by another washing of the paper, 
forms the required chloride of silver, on which he may obtain 
pictures by simple exposure in the copying frame ; with the 
third he gives permanency to the pictm-es which he produces. 



The power of destroying the susceptibility of a photographic 
ageut to the fiu-ther action of light, when the picture is com- 
pleted by its influence, is absokitely necessary for the perfection 
of the art. Various plans have been suggested for accomplishing 
this, which have been attended with very difierent results ; few, if 
any, of the materials used prodiicing the required effect, and, at the 
same time, leaving the pictiu-e unimpaired. The hyposulphite 
of soda is decidedly superior to every other fixing material ; but 
it will be interesting to name a few other preparations, which 
may be used with advantage in some instances. 

The pictiu'es formed on papei"s prepared with the nitrate of 
silver only, may be rendered permanent by washing them in 
very pui-e water. The water must be quite free from any 
chlorides, as these salts convert the nitrate of silver into a 
chloride, and attack the pictiu-e with considerable energy, and 
soon destroy it, by converting the darkened silver itself slowly 
into a chloride. Herschel remarks — " If the paper be prepared 
^vith the simple nitrate, the water must be distilled, since the 
smallest quantity of any muriatic salt present attacks the pictui-e 
impressed on such paper with singular energy, and speedily 
obliterates it, unless very dark. A solution containing only a 
thousandth part of its weight of common salt suffices to efiect 
this in a few minutes in a picture of considerable strength." 

The gi-eat point to be aimed at in fixing any of the sun- 
pictures is the removal of all that portion of the preparation, 
whatever it may be, which ha.s not undergone change, without 
distiu'bing those parts which have been altered in the slightest 
degi'ee by the chemical radiations. When a picture has been 
obtained upon paper prepared with the nitrate of silver, or the 
ammonio-nitrate of silver, the best mode of proceeding Ls to 
wash it first ^svith warm rain water, and then with a diluted 
solution of ammonia : if the ammonia is too strong it dissolves 
the oxide of silver, which in these processes is formed in the 
fainter parts of the pictm-e, and thus obliterates the more 
delicate portions. 

Photogi-aphs on the muriated papers are not, however, so 
easily fix:ed. Well soaking these in water dissolves out the 


excess of nitrate of silver, and tlius the sensibility is somewliat 
diniinislied ; indeed, they may be considered as half fixed, and 
may in this state be kept for any convenient opportunity of 
completing the operation. 

Chloride of sodium (common salt) was recommended by Mr. 
Talbot as a fixing material, but it seldom is perfectly successful : 
as a cheap and easy method, it may be occasionally adopted, when 
the pictiu'e to be preserved is not of any particidar consequence. 

It may appear strange to many that the same material which 
is used to give sensitiveness to the paper should be applied to 
destroy it. This is easily explained : In the first instance, it 
assists in the formation of the chloride of silver ; in the other, it 
dissolves out a large portion of that salt from the paper, the 
chloride of silver being soluble in a strong solution of chloride 
of sodium. The picture being first washed in water, is to be 
placed in the brine, and allowed to remain in it for some little 
time ; then, being taken out, is to be well washed in water, and 
slowly di'ied. After fixing by this process, the white parts of 
the photograph are often changed to a pale blue — a tint which 
is not, in some cases, at all unpleasant. 

I have in my possession some pictures which have been pre- 
pared more than eight years, which were then fixed with a 
strong solution of salt, and subsequently washed A\dtli warm 
water. They have become slightly blue in the white portions, 
but otherAvise they are very permanent ; and they have lost but 
little of their original character. 

The chloride of silver being soluble in a solution of ammonia, 
it has been recommended for fixing photographs. The ammonia, 
however, attacks the oxide, which forms the darkened parts 
in some preparations, so rapidly that there is great risk of its 
destroying the pictui-e, or, at least, of impairing it considerably. 
The only photographs on which I have used ammonia with com- 
plete success are those prepared with the phosphate of silver ; to 
many varieties it imparts a red tinge, which is fatal to their use 
for transfers. Still ammonia afibrds a ready means of 2:)artially 
fixing a photograph, and thus preserving it until a more con- 
venient period for giving it permanence. 

The ferrocyanide of potassium, or, as it is more commonly called, 
the 2Dru>ssiate of potash, converts the chloride into a cyanide of 
silver, which is not susceptible of change by light ; consequently 
this cheap salt has been employed as a fixing agent, but, most 
unfortimately, photographs which have been subjected to this 
preparation are slowly, but sm*ely, obliterated in the dark. 

The iodide of silver, which is readily formed by washing the 
photograph with a solution of the iodide of potassium, is scarcely 
sensitive to light ; and this salt, used in the proportions of five 


or six gi'ains to four or five ounces of water, ans-vrers tolerably 
■well "where transfers are not required. It tinges the Avhite lights 
of the pictui'e of a pale yello-w, — a colour which is extremely 
active in absorbing the chemical rays, and is therefore quite 
inapplicable where any copies of the original photograph are 
required. Bromide of potassium may be employed as a tempo- 
rary fixing agent, and for this purpose is strongly recommended 
by Mr. Talbot, and constantly employed by many of the con- 
tinental travelling photographers ; since it will insure the per- 
manence of an imjiression until an opportunity presents itself 
for giA*ing the final peraianence to the pictiire. 

Of all the fixing agents, the hyposulphite of soda is decidedly 
the best. This was first j^ointed out by Sir John Hei-schel, who 
also recommended that it should be used warm in some cases, 
which was the plan adopted by ]Mi\ Fox Talbot in the improve- 
ments of his calotype process. 

To use the hyposidj^hite of soda with efiect, there are several 
precautions necessary. In the fii'st place, all the free nitrate of 
silver must be dissolved out of the paper by well washing. The 
photograph being next spread on a plane sui'face, is to be washed 
over on both sides with a saturated solution of the hyposulphite 
of soda. The pictiire must then be washed, by allowing a small 
stream of water to flow over it, at the same time dabbing it vdih 
a piece of soft sponge, until the water passes ofi" perfectly taste- 
less. This opei'ation should be repeated twice, or, in particulai" 
cases, even thi'ee times. The hyposidphite of soda has the pro- 
perty of dissohdng a large quantity of several of the salts of 
silver, but paii;icul:Ti'ly of the chloride, with which it combines, 
forming a triple salt of an exceedingly sweet taste. This salt is 
liable to spontaneous decomposition, accompanied with separa- 
tion of silver in the state of sidphuret : hence the necessity of 
freeing the paper, by washing, of every trace of it, the sulphuret 
of silver being of a dirty bro'wn. It might appear that the use 
of warm water would more efiectually cleanse the paper ; but it 
often occasions the immediate formation of the sulphuret of silver. 

Some operators prefer leaviDg the picture in a bath of the 
hyposulphite of soda for some time, and then removing the salt 
by simple immersion in water, frequently changing it. The 
advantages of this appear to be, that the surface of the paper is 
not distiu'bed by any i-ubbing action, or by the mechanical ac- 
tion of water flowing over the siuiace. For fixing the calotype 
pictm-es, Mr. Cimdell, to whom we are miich indebted for im- 
provements in this particiilar process, recommends the following 
mode of manipulation : — 

The picture, or as many of them as there may be, is to be 
soaked in warm water, but not warmer than may be borne by 


the finger; this water is to be changed once or twice, and the 
pictures are then to be well drained, and either dried altogether, 
or pressed in clean and dry blotting-paper, to prepare them to 
imbibe a solution of the hyposulphite of soda, which may be 
made by dissolving an ounce of that salt in a quart of watei\ 
Having poured a little of the solution into a flat dish, the 
pictm^es are to be introduced one by one; daylight ^\dll not now 
injure them : let them soak for two or three minutes, or even 
longer, if strongly j^rinted, turning and mo^dng them occasion- 
ally. The remaining um-educed salts of silver are thus thoroughly 
removed by soaking in water and pressing in clean blotting- 
paper alternately ; but if time can be allowed, soaking in water 
alone will have the effect in twelve or twenty-four hours, ac- 
cording to the thickness of the paper. It is essential to the 
success of the fixing process, that the paper be in the first place 
thoroughly penetrated by the hyposulphite, and the sensitive 
matter dissolved; and next, that the hyposidphite compoimds 
be effectually i-emoved. Unless these salts are completely 
washed out, they induce a destructive change upon the pictm-e; 
they become opaque in the tissue of the paper, and unfit it for 
the operation of being copied. 

Mucli has been said and written about improving the tone of 
the pictiu'e by the use of old hyposulphite of soda, and of 
the hyposulphite in which chloride of silver has been dissolved. 
My own experience, which is corroborated by that of many of 
the most successfid photographic artists in England and on the 
continent, convinces me, that in aiming at pecuHarity of tint by 
these methods, the permanency of the photogi'aph is injured. 
I have pictm-es, produced by different ai-tists, fiied after this 
method, and scarcely one of them remains free from change. 

The object is to remove all the chloride or iodide of silver; 
and to secui-e this, as much hyposulphite of soda should be un- 
conibhied, with chloride or ioclide of silver, in the solution as 

The hyposulphite of silver being formed, it has to be dissolved 
out of the paper, the fibres of which hold it with a strong capil- 
lary force ; and it is only by very long continued soaking that 
all can be removed. The slight mechanical aid afforded by 
dapping the siu-face of the paper ^vith a soft sponge well filled 
with water, gTeatly accelerates the removal of the salt ; and 
when the paper ceases to taste sweet, we may depend ujjon the 
permanence of the photograph. 

The hy|50sidphite of soda has been used for almost every pho- 
tographic process, from the facility it affords for removing the 
silver salts. The following is the process of Gustave le Gray, 
of Paris, chiefly applicable to the calotype process on waxed 


paper, "wliicli is valuable as being the directions of one who has 
produced most beaxitiftil pictiu-es : but it does not differ, in any- 
important particulars, from the j^rocess already given : — 

" Make in a bottle the following solution : — Filtered Avater, 
about a pint and a half; hyposulphite of soda, about three 
ounces ; cover the bottom of a dish with this, and pkmge in 
your negative proof, taking care to avoid au--bubbles : this dis- 
solves the bromo-chloro-iodide of silver, but does not attack the 
gallo-nitrate of silver, which foinns the blacks. — [Le Gray is in 
eiTor here, and in a succeeding pai'agraph — the darkened por- 
tions of these photogi-aphs being metallic, silver in a state of 
extreme division.] 

" Never put more than one proof at a time in the bath ; but 
you may use it for several proofs one after the other. 

" If you examine the proof as a transparency after it has re- 
mained some time in the bath, you may be tempted to think it 
is lost, as in some places spots will appear from the iodide of 
sUver not being completely taken away ; but if you wait until 
it is removed, which you will know by the disappearance of the 
yellow tint, you will be astonished at the whiteness and trans- 
parency of the paper, as well as at the beauty of the blacks in 
the image. 

" It will require for this, to remain in the bath from half an 
hovu- to three quarters ; you will then wash it ia several waters, 
and leave it ia a basin of clear water for three quarters of an 
hour ; then let it dry spontaneously by hanging it up ; the proof 
is then quite unalterable by light, as thei'e remains nothing more 
in the paper than the gallo-nitrate of silver, which is black. 
(See above.) 

" Fixing by means of the bromide of potassium is not so 
dvu'able, because it does not remove any of the materials used 
in prepariug the pajier. It may, nevei-theless, be of great use 
in travelling, and when it is required to make several proofs one 
after the other; because then you avoid touching the hyposiil- 
phite in preparing the negative paper, which spots at the least 
contact -with it. 

" You may thus place the whole of yoiu' negative proofs 
together in this bath. 

"Water, a jiint and tlu-ee quarters; bromide of potassium, 
360 grains. 

" In taking the proof oiit of the bath, yovi must wash it in 
several waters, and dry it; it should be kept in the bath at 
least tlu-ee quarters of an houi-, but if you leave it in two or 
three hoiu"s, it will not injiu-e it." 

Such is M. le Gray's statement, and so it is rendex'ed by his 


English translator, Mr. Cousins; but I believe tlie quantity of 
the bromide of potassium to be by far too large, and that the 
pictures would sustain less injury by using a solution of one 
half the strength indicated. His process for fixing the positive 
pictures contains some important hints. 

"Dissolve in a bottle hyposulphite of soda, 1500 grains ; 
" Filtered water, nearly a quart. 
In another bottle dissolve 75 grains of nitrate of silver in a 
wine-glass or two of water; when well dissolved, you add to 
it a satiirated solution of chloride of sodium, until the white 
precipitate ceases to fall ; allow it to repose a shoi-t time, and 
then decant the clear liquor, and gather the precipitate of chlo- 
ride of silver, which you dissolve in the other bottle of hypo- 
sulphite of soda; by means of this solution you obtain directly 
black tints upon the picture. The older the hyposulphite of 
soda is, the better; when it gets thick, you must add a fresh 
solution of hyposulphite alone, without the chloride of silver, 
the old containing an excess, which it has taken from the proofs 
already immersed in it. You must not filter it to take away 
the deposit, but only let it repose in a large bottle, and decant 
the clear liquid for use, leaving the sediment to be re-dissolved 
by fresh solution. 

" By leaving the proofs a longer or shorter period in the bath, 
you can obtain all the tints from the red to the black, and clear 
yellow; with a little practice, you will be siu-e to get the tint 
you desire. You must not leave a proof less than an hour 
in the bath for it to be sufficiently fixed, and it can remain 
three or four days to obtain the sepia and yellow. By heating 
the hyposulphite of soda I accelerate the operation; but we 
must not then leave the proof for an instant to itself, as the 
rapidity of action is so great, that the picture might be com- 
pletely efiaced. 

" By adding to the preceding solution about one fluid ounce 
of liquid ammonia, I obtain pretty bister tints, and very pure 
whites. The English paper is exceedingly good for these tints. 

" I obtain also fine velvet-like tints by putting the photo- 
gi'aph (when taken out of the hyposulphite of soda) upon a bath 
of a salt of gold, using 15 grains of the chloride of gold to oiie 
pint and a half of distilled water. 

" Fine yellow tints are obtained by placing the proof (if too 
vigorous) first in a bath of hyposulphite, and then in a bath 
composed of one pint and a half of water, and one fiuid ounce 
and a half of hydrochloric acid ; washing it perfectly in water. 
Liquid ammonia, employed in the same quantity as last men- 
tioned, gives remarkably fine tints. 


" When the proof is the colour you desire, wash it in several 
waters, and leave it two or three hom"s in a basia of water, until, 
touching it v\'ith the tongue, you perceive no sweet taste, which 
indicates the presence of hyposulphite of silver; then diy it by 
hanging it up, and it is tinished. The bath may contain as 
many proofs as can be conveniently placed in it." 

Experience has shown, that however beautiful may be some 
of the tones given to a photograph by the methods recommended 
by M. Le Gray, these are obtained with some sacrifice of per- 
manency. Many choice productions prepared by this photo- 
grapher, which I have had for but a few months in my 
possession, are showing indications of decay : the change taking 
place first at the edges, and gradually creeping over the whole 

The following fixing processes are rather more cuiious than 
useful : they were fii'st indicated by Su- John Herschel, from 
whose memoir on the Chemical Agency of the Bays of the ^'olar 
^'jjectrum, I quote: — 

" By far the most remarkable fixing process vdth wliich I am 
acquainted, however, consists in wasliing over the pictui'e with 
a weak sokition of corrosive sublimate, and then laying it for 
a few moments in water. This at once and completely obliter- 
ates the picture, reducmg it to the state of perfectly white 
paper, on which the nicest examination (if the process be per- 
fectly executed) can detect no trace, and in which it may be 
used for any other purpose, as ch-a^dng, A\Titing, &g., being com- 
jjletely insensible to light. Nevertheless, the jDictui'e, though 
invisible, is only dormant, and may be instantly revived in all 
its force by merely brushing it over with a solution of a neutral 
hyposTilphite, after which, however, it remains as insensible as 
before to the action of light. And thus it may be successively 
obliterated and revived as often as we please. It hardly requires 
mention that the property in question furnishes a means of 
painting in mezzotinto (i.e., of commencing on black paper and 
working in the lights), as also a mode of secz'et writing, and a 
variety of similar applications." 

, There is a remark which ought not to be omitted in regard 
to this part of our subject, viz., that it makes a gi-eat difierence, 
in respect of the injuiy done to a photographic picture by 
the fixing process, whether that picture has been impressed by 
the long-continued action of a feeble light, or by the quick 
and vivid one of a bright sun. Even supposing the pictures 
originally of equal intensity, the half-tints are much less power- 
fully corroded or washed out in fixing in the latter case than in 
the former. 


Section I. — The Calotype as now Practised, and its 

In the historical section, the description of the calotype, as pub- 
lished by Mr. Fox Talbot, is given. Mr. Hemy Fox Talbot, 
duiing 1852, made the country a free gift of all his patents, 
reserving only the right of a patentee over that portion which 
includes the practice of taking portraits for sale. (See the 
letters in the Api:)endix.) 

The fii'st important published improvement on the calotype 
was due to ]Mi\ Cundell, whose process appeared in the Philo- 
sophical Magazine for May, 1844, from which we extract the 
following : — 

1. To produce a calotype picture, there are five distinct pro- 
cesses, all of wliich, except the third, must be performed by 
candle-light : they are all very simple, but, at the same time, 
they all requii*e care and caution. The first, and not the least 
important, is — 

3. The Iodizing of the Paper. — Much depends upon the 
paper selected for the purpose ; it must be of a compact and 
uniform texture, smooth and transparent, and of not less than 
mediiim thickness. The best I have met Avith is a fine satin post 
paper, made by " P. Tui-ner, ChafFord Mill." Having selected 
a half-sheet without flaw or water-mark, and free from even the 
minutest black specks, the object is to spread over its surface a 
perfectly uniform coating of the iodide of silvei-, by the mutual 
decomposition of two salts, nitrate of silver and iodide of potas- 
sium. There is a considerable latitude in the degree of dilu- 
tion in which these salts may be used, and also in the manner 
and order of their application ; but as the thickness and regu- 
lai'ity of the coating depend upon the solution of nitrate of 
silver, and upon the manner in which it is applied, I think it 
ought by all means to be applied first, before the surface of the 
paper is disturbed. I use a solution of the strength of seventeen 
grains to the ounce of distilled water. 

3. The paper may be pinned by its two upper comers to a 

jiE. cuxdell's calottpe process. 207 

clean thy board a little larger than itself; and, holding this nearly 
upright in the left hand, and commencing at the top, apply a 
wash of the nitrate of silver thoroughly, evenly, and smoothly, 
with a large soft binish, taking care that every part of the sui*- 
face be thoroughly wetted, and that nothing remain unabsorbed 
in the natiu'e of free or running solution. Let the paj:)er now 
hang loose from the board into the aii* to dry, and by using sevei-al 
boards time will be saved. 

4. The nitrate of silver spread upon the paper is now to be 
saturated with iodine, by bringing it in contact with a solution 
of the iodide of potassium : the iodine goes to the silver, and the 
nitric acid to the potash. 

5. Take a solution of the iodide of potassium of the strength 
of 400 grains to a pint of water, to which it is an improvement, 
analogous to that of M. Claudet in the daguerreotype, to add 
100 grains of common salt. He found that the chlorinated 
iodide of silver Ls infinitely more sensitive than the simple iodide; 
and by this addition of common salt, a similar, though a less re- 
markable, modification is obtained of the sensitive compound. 
Pom* the solution into a shallow flat-bottomed dish, sufficiently 
large to admit the paper, and let the bottom of the vessel be 
covered to the depth of an eighth of an inch. The prepared side 
of the paper, having been previously marked, is to be brought in 
contact with the surface of the solution, and, as it is desirable to 
keep the other side clean and diy, it ^vill be found convenient, 
before putting it in the iodine, to fold upwards a naiTow margin 
along the two opposite edges. Holding by the uptm-ned margin, 
the paper is to be gently di-awn along the surface of the liquid 
untn its lower face be thoroughly wetted on every part ; it will 
become plastic, and in that state may be sufiered to repose for a 
few moments in contact with the liquid : it ought not, however, 
to be exposed in the iodine dish for more than a minute 
altogether, as the new compound, just fonned upon the paj)er, 
upon farther exposure, would gTadually be rechssolved. The 
paper is therefore to be removed, and, after diipping, it may be 
placed upon any clean surface with the wet side uppeiTaost imtil 
about half dry, by which time the iodine solution "wtJI have 
thoroughly penetrated the paper, and have found out and 
saturated every particle of the silver, wliich it is quite indis- 
pensable it should do, as the smallest portion of undecomposed 
nitrate of sdver would become a black stain in a subsequent part 
of the process. 

6, The paper is now covered with a coating of the iodide of 
silver ; but it is also covered, and indeed satm-ated, with saltjjetre 
and the iodide of potassium, both of which it is indispensable 


should be completely removed. To effect the removal of these 
salts, it is by no means sufficient to " dip the paper in water ; " 
neither is it a good plan to wash the paper with any considei'able 
motion, as the iodide of silver, having but little adhesion to it, is 
apt to be washed off. But the margin of the paper being still 
upturned, and the unprepared side of it kept dry, it will be found 
that by setting it afloat on a dish of clean water, and allowing it 
to remain for five or ten minutes, dra^\dng it gently now and 
then along the surface to assist in remo\"ing the soluble salts, 
these will separate by their own gravity, and (the iodide of silver 
being insoluble in water) nothing will remain upon the paper 
but a beautifully perfect coating of the kind required. 

7. The paper is now to be dried ; but, while wet, do not on 
any account touch or disturb the prepared surface with blotting 
paper, or with anything else. Let it merely be suspended in the 
air ; and, in the absence of a better expedient, it may be planed 
across a string by one of its corners. When dry, it may be 
smoothed by pressure. It is now " iodized" and ready for use, 
and in this state it will keep for any length of time if protected 
from the light. The second process is that of exciting or 

8. Preparing the Paper for the Camera.— For tliis purpose 
are i-equiied the two solutions described by j\Ir. Talbot ; namely, 
a satui-ated solution of ciystallized gallic acid in cold distilled 
water, and a solution of the nitrate of silver of the sirengih of 
50 grains to the ounce of distilled water, to which is added one- 
sixth part of its volimie of glacial acetic acid. For many 
]:)ui'poses these solutions are unnecessarily strong, and, unless 
skilfully handled, they are apt to stain or embroA\Ti the paper : 
where extreme sensitiveness, therefore, is not required, they may 
with advantage be diluted to half the strength, in which state 
they are more manageable and nearly as effective. The gallic 
acid solution will not keep for more than a few days, and only a 
small quantity, therefore, shoidd be prepared at a time. When 
these solutions are about to be applied to the iodized paper, they 
are to be mixed together, in equal volumes, by means of a gra- 
duated di-achm tube. This mixtm-e is called "the gallo-nitrate of 
sUver." As it speedily changes, and ■wdll not keep for more than 
a few minutes, it must be used without delay, and it ought not 
to be prepared untU the operator is quite- ready to apply it. 

9. The application of this "gallo-nitrate" to the paper is a 
matter of some nicety. It ^v'ill be found best to apply it in the 
following manner : — Poiu* out the solution upon a clean slab of 
plate-glass, diffusing it over the sm-face to a size corresponding 
to that of the paper. Holding the paper by a narrow upturned 
margin, the seuaitive side is to be applied to the liquid upon the 

MK. cundell's process. 209 

slab, and brought in contact with it by passing the fingers gently- 
over the back of the paper, which mvist not be touched with the 

10. As soon as the paper is ivetted with the gallo-nitrate, it 
ought instantly to be removed into a dish of water ; five or ten 
seconds at the most is as long as it is safe at this stage to leave 
the paper to be acted upon by the gallo-nitrate ; in that space 
of time it absorbs sufficient to render it exquisitely sensitive. 
The excess of gallo-nitrate must immediately be washed off by 
di"a^ving the paper gently several times under the surface of 
water, which mvist be perfectly clean ; and being thus washed, 
it is finished by di-a-wTng it through fresh water, two or thi-ee 
times, once more. It is now to be diied in the dark, in the 
manner described in § 7 ; and, when siu*face-diy, it may either be 
placed, while .still damp, in the camera, or in a portfolio, among 
blotting-paper, for use. If properly prepared, it will keej) per- 
fectly well for four-and-twenty hoiu-s at least, preserving aU its 
whiteness and sensibility. 

11. The light of a single candle will not injure the paper at a 
moderate distance ; but the less the paper, or the exciting solu- 
tion, is unnecessarily exposed, even to a feeble candle-light, the 
better. Common river or spring water answers perfectly to 
wash the paper, distilled water being requii'ed for the silver solu- 
tions only. 

Stains of "gallo-nitrate," while recent, may be removed from 
the fingers by a little strong ammonia, or by the cyanide of 

The tliu'd process is that of 

12. The Exposure in the Camera, for which, as the operator 
must be guided by his ovn\ judgment, few directions can be 
given, and few are requii-ed. He must choose or design his ovm 
subject ; he must detex-mine upon the aperture to be used, and 
judge of the time requii-ed, which will vary from a few seconds 
to three or four minutes. The subject ought, if possible, to have 
a strong and decided efiect ; but extreme lights, or light-coloiu-ed 
bodies, in masses, are by all means to be avoided. When the 
paper is taken from the camei'a, very little, or more commonly 
no trace whatever, of a picture is visible until it has been sub- 
jected to the fourth process, which is 

13. The Bringing-out of the Picture, which is effected by 
again applying the " gallo-nitrate " in the mamier directed in 
§ 9. As soon as the paper is wetted all over, unless the pictvu-e 
appear immediately, it is to be exposed to the radiant heat from 
an iron, or any similar body, held within an inch or two by an 
assistant. It ought to be held vertically, as well as the paper ; 


and the latter ouglit to be movecl, so as to prevent any one part 
of it becoming diy before the rest. 

As soon as the pictiire is snffieiently brought out, wash it 
inxmecliatelj in clean "water to remove the gallo-nitrate, as 
directed in § 10 ; it may then be placed in a dish, by itself, ii.nder 
water, until yon are ready to fix it. Tha most perfect pictures 
ai*e those which '•' come out " before any part of the paper 
becomes dry, which they will do if sufficiently impressed in the 
camera. If the paper be allowed to diy before washing off the 
gallo-nitrate, the lights sink and become opaque ; and if exposed 
in the dry state to heat, the paper will embrown ; the diying, 
therefore, ought to be retarded, by wetting the back of the 
paper, or the picture may be brought out by the vapoiu' from 
hot water, or, what is better, a horizontal jet of steam. The 
fifth and last process is 

14. The Fixing of the Picture, which is accomplished by 
removing the sensitive matter from the paper. The picture, or 
as many of them as there may be, is to be soaked in warm water, 
but not wamier than may be borne by the fiuger ; this water is 
to be changed once or twice, and the pictiu-es ai-e then to be well 
di-ained, and either diied altogether, or pressed in clean and diy 
blotting-paper, to prepare them to imbibe a solution of the 
hyposulphite of soda, which may be made by dissolving an ounce 
of that salt in a qiiart (forty ounces) of water. Having poiu-ed 
a little of the solution into a flat dish, the pictures are to be 
introduced into it one by one ; daylight wiU not now injure them; 
let them soak for two or three minutes, or even longer if strongly 
printed, tm-ning and mo^-ing them occasionally. The remaining 
uni'educed salts of silver are thus thoroughly dissolved, and may 
now, with the hyposulphite, be entirely removed by soaking in 
water and 2)ressrn(/ in clean white blotting-paper alternately; 
but if time can be allowed, soaking in water alone vriR have the 
effect in twelve or twenty-four hoiu-s, according to the thickness 
of the paper. It is essential to the success of the fixing process 
that the paper be in the fii-st place thoroughly penetrated by the 
hyposulphite, and the sensitive matter dissolved ; and next, that 
the hyposulphite compounds be eftectually removed. Unless 
these salts are completely removed, they inditce a destiiictive 
change upon the pietiu-e ; they become opaque in the tissue of 
the paper, and entirely imfit it for the next, which is 

15. The Printing Process. — The pictm-e being thus fixed, it 
has merely to lie dried and smoothed, when it will undergo no 
further change. It is, however, a negative pictm-e, and if it have 
cost some trouble to produce it, that trouble ought not to be 
gi'udged, considering that you are now possessed of a matrix 

ME. cumdell's process. 211 

which is capable of yielding a vast niunber of beautiful im- 
jDressions. I have had as many as fifty piinted ii*om one, and I 
have no doubt that as many more might be obtained from it. 

1 6. The manner of obtaining these impressions have been so 
often described, and there are so many different modes of 
jDroceeding, that it may be siifficient to notice veiy briefly the 
best process with which I am acquainted. Photography is 
indebted for it to Dr. Alfi-erl Taylor. His solution is made by 
dissolving one part of nitrate of silver in twelve of distilled 
water, and gradually adding strong Hquid ammonia until the 
precipitate at fii-st produced is at length just redissolved. 

17. Some paper is to be met with, containing traces of bleach- 
ing chlorides, which does not require any previous preparation ; 
but in general it will be foimd necessary to prepare the paper 
by slightly impregnating it with a minute quantity of common 
salt. This may be done by dipping it in a solution in which the 
salt can barely be tasted, or of the strength of from thirty to 
forty grains to a j)int of water. The paper, after being pressed 
in clean blotting-paper, has merely to be cfried and smoothed, 
when it will be fit for use. 

1 8. The ammonia-nitrate of silver is applied to the paper in 
the manner described in § 3 ; and, when perfectly dry, the 
negative pictm-e to be coj^ied is to be applied to it, with its face 
in contact with the sensitive side. The back of the negative 
picture being upj^ermost, they are to be pressed into close 
contact by means of a plate of glass ; and, thus seciired, they are 
to be exposed to the fight of the sun and sky. The exposed 
parts of the sensitive paper will speedily change to lilac, slate- 
blue, deepening towards black ; and the light, gradually pene- 
trating through the semi-transparent negative picture, will 
impiint upon the sensitive paper beneath a positive impression. 
The negative picture, or matrix, being, slightly tacked to the 
sensitive paper by two mere particles of wafer, the progress of 
the operation may from time to time be observed, and stopped 
at the moment when the pictvire is finished. 

19. It ought then, as soon as possible, to be soaked in warm 
water, and fixed in the manner described in § 1 4. 

20. In theses pictiu-es there is a cmious and beautifrxl variety 
in the tints of colour they M-iU occasionally assimie, varying from 
a rich golden orange to pm-ple and black. This effect depends 
in a great degree upon the paper itself ; but it is modified con- 
siderably by the strength of the hyposulphite, the length of the 
time exposed to it, by the capacity of the paper to imbibe it, 
and partly, perhaps, by the nature of the light. "Warm sepia- 
coloured pictures may generally be obtained by cfrying the 


paper, by pressure, and maldng it imbibe tbe liyposulpliite 
supplied iu liberal quantity. 

The paper of " I. Whatman, Tm-key Mill," seems to give 
pictures of the finest colour, and, upon the whole, to answer best 
for the purpose. 

If the chemical agents employed be piu'e, the operator, who 
keeps in view the intention of each separate process, and either 
adopting the manipulation recommended, or improving upon it 
fi-om his own resom-ces, may rely with confidence upon a satis- 
factory result. 

This calotype paper is so exceedingly sensitive to the influence 
of light, that very beautiful photographic copies of lace, feathers, 
leaves, and such like articles, may be made by the light of a 
common coal-gas flame, or an Argand lamp. The mode of pro- 
ceeding is precisely that described for obtaining the ordinary 
photographic drawings by daylight, only substituting the calotype 
paper, which shoidd be damp, for the common photographic. 

When exposing the prepared paper to the light, it should be 
held about four or five inches from the flame, and the time 
required will be about three minutes. 

Bvit little remains to be added to this very clear and satisfac- 
tory description of the calotype process, — to which, indeed, is 
mainly due the perfection to which it has arrived both at home 
and abi'oad. 

There are, however, a few modifications which must be noticed, 
as tending to simplify the details in some cases, and to improve 
the general effects in others. In the main, however, it will be 
foimd that Mr. Cimdell's process of manipulation is almost as 
good as any that can be adopted : and that gentleman certainly 
merits the thanks of the patentee, and of all photographic artists. 

Many modifications of Mr. Talbot's mode of manipulating 
have been introduced with very variable advantages. I have, 
however, found that nearly every variety of paj^er requires some 
peculiar method to excite it to its maximiun degree of sensi- 
bility. A few of the published methods may be noticed, as, 
mider dilferent circumstances, they may prove useful. 

Mr. Robert Bingham, who has operated with such success, 
adopts the following process : — 

Apply to the paper a solution of nitrate of silver, containing 
100 grains of that salt to 1 ounce of distilled water. When 
nearly, but not quite diy, dip it into a solution of iodide of 
potassium, of the strength of 2o grains of the salt to 1 ounce of 
distilled water, ckain it, wash it, and then allow it to dry. Now 


Lnish it over with aceto-niti-ate of si]\^er, made hj dissolving 
50 grains of nitrate of silver in 1 ounce of distilled water, to 
Avhich is added one-sixth its volnme of strong acetic acid. Dry- 
it with bibulous paper, and it is now ready for receiving the 
image. When the impression has been received, it must be 
washed with a satiu-ated solution of gallic acid, and exposed to 
a steam heat, a jet of steam from the spout of a tea-kettle, or 
any convenient vessel. The image will be gradually brought 
out, and may be fixed with hyposulphite of soda. It will be 
observed that in this process the solutions of nitrate of silver 
and of gallic acid are not mixed before application to the paper, 
as in Mr. Talbot's process. 

Mr. Chaiming, of Boston, very much simplified the calotype 
process. He dii-ects that the paper should be first washed over 
with 60 grains of crystallized nitrate of silver, dissolved in 1 ounce 
of distilled water, and when dry, with a solution of 10 grains 
of the iodide of potassium in 1 ounce of water : it is then to 
be washed with watei-, and dried between folds of blotting paper : 
the sensibility of the paper is correctly said to be much im- 
proved by combining a little chloride of sodium with the iodide 
of potassium : 5 grains of the latter salt, and rather less than 
this of the former, in an oimce of water, may be employed 

To vise this paper of Mr. Channing's, where time is an object, 
it is necessary to wash it immediately before it is placed in the 
camera obscura, with a weak solution of nitrate of silver, to 
which a drop or two only of gallic acid has been added. The 
picture is subsequently developed by the gaUo-nitrate of silver, 
as already described. 

Blanquart Everard, Sagnez, and some others, have recom- 
mended that in the preparation of the highly sensitive photo- 
gTaphic papers no brushes should be employed. They pursue 
the following plan : the solutions are pom-ed upon a perfectly 
flat piece "of glass, and the paper carefully drawn over it, and, if 
necessary, jjressed closer by another plate of glass. 

A plan of iodizing paper has been proposed by , Mr. Jordan, 
which offers many advantages. Iodide of silver is pi-ecipitated 
from the solution of the nitrate by iodide of potassium, and this 
precipitate being lightly washed, is redissolved in a strong 
solution of the latter salt. This solution is applied to the paper, 
and the paper allowed to chy ; after this it is placed face down- 
wards upon some clean water ; the iodide of potassium is 
removed by this, and a pure iodide of silver left on the paper. 

If the paper carefully and properly iodized is washed with a 
very dilute solution of the aceto-nitrate of silver, that is to say, 


with a solution composed of 10 grains of nitrate of silver to 
1 fluid ounce of distilled water, and 10 drops of a concentrated 
solution of gallic acid be added to anotlier ounce of distilled 
water and the two mixed, it will keep for three weeks or a 
month. It may be used dry in the camera, and afterwards 
developed with the gallo-nitrate in the usual manner. It will, 
however, require an exposure in the camei'a of from ten to 
twenty minutes, and is, therefore, only usefid for still objects ; 
but for buildings, landscapes, foKage, and the like, nothing can 
be more beautifrd. 

Le Gray recommends as a highly sensitive paper for portraits 
the following : — 

Distilled water 6200 grains. 

Iodide of potassium .... 300 „ 

Cyanide of potassium ... 30 „ 

Fluoride of potassium ... 1 j> 

Papers are washed with this, and then ^dth his strong solution 
of aceto-nitrate of silver, which is described in the section 
devoted to the wax paper j^rocess. 

M. A. Martin, who is aided by the Imperial Academy of 
Sciences of Vienna in his endeavours to improve the jihoto- 
graphic processes, and render them available to the pm*poses of 
art, has published the following as the best proportions in which 
the solutions should be made, and the order of their apjjlication. 

For the negative pictiu'e — 

First. Iodide of potassium g oz. 

Distilled water 10 fluid oz. 

Concentrated solution of cvanide ) „ -, 
n . ■ - - 7 droiis. 

oi potassium j '■ 

Second. Nitrate of silver 7 di'achms. 

Distilled water 10 fluid oz. 

Strong acetic acid 2 drachms. 

Third. A concentrated solution of gallic acid. 

Fourth. Good spirits of wine. 

Fifih. Hyposulphite of soda . . . . 1 oz. 

DistUled water 10 fluid oz. 


For the positive pictures — 

First. Chloride of sodium .... 168 grains. 
Distilled water 10 oz. 

Second. Nitrate of silver . . . . 1 oz. 

Distilled water 10 oz. 

Third. Hjrposulphite of soda .... 1 oz. 

Distilled water 40 oz. 

Nitrate of silver 30 grains, dissolved in ^ oz. of distilled 
water, to be pouied into the solution, in a small stream, while 
it is constantly stnred with a glass rod. 

Martia particularly recommends the application of the iodine 
salt fii'st to the paper, drying this, then applying the argentine 
solution, and drying rapidly. I have m-ged the necessity of 
this on several occasions : the advantages are, that the iodide of 
silver is left on the very sm-face of the paper ready for the 
influence of the sHghtest chemical radiation. 

The prodiictions of M. Flacheron, which were seen in the 
Great Exhibition, excited much interest, and the process by 
which these were obtained in the Eternal City was eagerly 
sought for by photogi-aphic amateiu-s. In the Art Journal for 
May, Mr. Thomas has communicated the process by which the 
photographers of Rome pi'oduce their best eflects ; and as this is 
important, as being useful in hot climates, a sufficient portion 
of that communication is transfen-ed to these pages. 

"\st. Select old and thiu Euglish paper — I prefer "Whatman's: 
cut it in such a maimer that the sheet shall be the sixteenth of 
an inch smaller than the glass of the paper-holder on every side, 
and leave two ends at diagonal comers to the sheet by which to 
handle it. 

" 2dly. Prepare the following solution : — 

"Saturated solution of iodide of potassiiun 2| fluid di-achms: 
pure iodide 9 grains: dissolve. 

"Then add, distilled water 11^ ounces, iodide of potassiimi 4 
drachms, bromide of potassium 1 gi'ains, and mix. Now, filter 
this solution into a shallow porcelain vessel somewhat lai'ger 
than the sheet of paper to be prepared. Take a piece by the two 
diagonal ends, and gently place the end of the marked side 
nearest to you, upon the surface of the bath ; then carefully 
incline the surface of the sheet to the liquid, and allow it to rest 
two minutes ; if French paper, one minute, or until the back of 


tlie paper (not \rettecl) becomes tiiited iinifomily by the action 
of tbe dark-coloiu'ed solution. Raise it up by means of the two 
ends occasionally, in order to cliase away any au*-bubbles, which 
would be indicated by white spots on the back, showing that the 
solution in these parts has not been absorbed. Hold the paper 
by one of the ends for a minute or so, in order that the siiper- 
fluous moistui"e may run off, then hang up to diy, by pinning 
the one end to a string run across a room, and let the excess di'op 
off at the diagonal corner. When dry the paper is ready for 
use, and quite tinted with iodine on both sides. It will keep 
any length of time, and is much improved by age. 

" 2idly. I T\T.ll presume that four sheets are to be excited for 
the camera, and that the operator has two double paper-holders, 
made without a wooden partition, the interior capacity of which 
is sufficiently large to admit of three glasses, all movable. The 
third, as will be seen, is to prevent the two pieces of excited 
paper coming in contact with each other. 

" Prepare the following solution : — 

'• Take nitrate of silver 2^ di-achms ; acetic-acid 4| drachms ; 
distilled water 3^ omices : mix and dissolve. 

" Now take four of the glasses of the liaper-holders perfectly 
clean, and place each upon a piece of common blotting-paper to 
absorb any little excess of liquid. Pom" about 1^ drachms, or 
rather more of the solution just prepared, into a small glass 
funnel, into which a filter of white bibulous paper has been 
placed, and let the solution filter drop by di-op upon glass No. 1, 
imtil about 1| drachms have been filtered in detached drops, 
regularly placed upon its siu'fice : then, with a sHp of jDaper, 
cause the liquid to be diffused over the whole siu-face of the 
glass. Take a piece of prepared paper, and place it marked, side 
downwards, uj)on a glass just prepared, beginning at the end 
nearest you, and thus chasing out the air. Draw it up once or 
twice by its two diagonal corners ; allow it to rest, and jirepare 
glass No. 2 in a similar manner. Now look at glass No. 1, and 
it will be pez'ceived that the \-iolet tint of the paper has become 
mottled ^vith patches of white, which gradually spread, and in a 
few seconds the paper resumes its original whiteness, which is an 
indication that it is ready for the camera. It ^vill be found to 
adhere firmly to the glass. Do not remove it ; but hold the 
glass np to allow the excess of fiuid to iim off at one comer. It 
must not be touched with blotting-paper, but replaced flat on 
the table. Sex-ve Nos. 2, 3, and 4, in like manner. Take foiir 
pieces of common white paper, not too much sized, free from ii'on 
spots, and cut a trifle smaller than the prepared sheet ; soak 
them in distilled water ; draw out one piece, hold it up by the 

ME. muller's process. 217 

fingers to drain off suiierfluous moistiire, and place it gently upon 
the back of the prepared paper. AVith another piece of glass 
kept for the purpose, having the edge rounded, and large enoixgh 
to act uniformly upon the paper, scrape off gently the excess of 
liquid, beginning at the top of the sheet, and removing viith the 
rounded edge of the scraper the liquid to one of the corners. 
Repeat this operation t^^-ice. Both the excited and superim- 
posed paper are thus fixed to the glass. • Two glasses and papers 
being thus prepared, take the clean glass Ko. 5, and place upon 
No. 1 : press gently : the moist paper will cause it to adhere. 
Take up the two glasses thus afiixed and place them upon glass 
'No. 2, in such a manner that the supernumeraiy glass No. 5 
shall be in the centre. The whole will form a compact body, 
and having polished the sm-faces, and wiped the edges, may at 
once be put in the paper-holders. * * * 

" ithly. With a Ross's, ChevaKer's, or Lerebours' single lens, 
three inches diameter, and half an inch diaphi-agm, the object 
to be copied, well lighted by the sun, the paper will require from 
four to six minutes' exposure. 

" 5thly. Take out the three glasses, which will still firmly 
adhere, sepai-ate them gently, and remove the piece of moistened 
paper, which must not be vised again. Now lift up the prepared 
paper by one comer to the extent of half the glass, and pour 
into the centre about one drachm of a satiu-ated solution of 
gaUic acid, which will immediately difluse itself Raise also the 
other corner to facilitate its extension ; and sei-ve the othei-s in 
like manner. The image takes generally from ten to twenty 
minutes to develope. Hold iip the glass to a candle to watch 
its intensity. When sufficiently developed remove the negative 
from the glass. Wash it in two or thi-ee waters for a few hours, 
(by with blotting-paper, and immerse each separately for ten 
minutes in a bath of bromide of potassium in solution : then 
wash and dry. , 

" The iodide may be removed by means of hyposulphite of soda 
in the usual way, twelve months afterwards, or when convenient. 
If," says Mr. Thomas, " the process has been carefidly conducted, 
four beautiful negatives must be the result. I was ten days 
working incessantly at Pompeii, and scarcely ever knew what a 
failure was." 

IVIr. MuUer, a gentleman who has been practising photography 
with great success at Patna, in the East Indies, has communi- 
cated his process to me, which is as follows : — 

A solution of hydi'iodate of iron is made in the proportions 
of 8 or 10 grains of iodide of iron to 1 ounce of water; this 


solution is prepared in the ordinary way, with iodine, iron turn- 
ings, and water. The ordinary paper employed in photogpraphy 
is washed on one side with a solution of nitrate of lead (15 grains 
of the salt to 1 ounce of water) ; when dry, this paper is iodized 
either by immersing it completely in the solution of the hydi-io- 
date of iron, or by floating the leaded sm-face on the solution. 
It is removed after a minute or two, and lightly di-ied with 
blotting-paper. The paper now contains iodide of lead and j)roto- 
nitrate of iron : while still moist it is rendered sensitive by a 
solution of nitrate of silver (100 grains to the ounce of water) 
and j^laced in the camera. After the ordinaiy exposui'e it may 
be removed to a dark room ; if the image is not ah-eady deve- 
loped, it will be found speedily to appear in great sharpness 
without any further application. It may then be fixed with the 
hyposulphite of soda in the usual manner. 

In December 1852 Sir John Herschel communicated to the 
pages of the AthencEum a letter from his brother-in-law, Mr. 
Stewart, a resident at Pau, in the Pyrenees. In this he states, 
that, at the stiggestion of Professor Regnault, he was induced to 
adopt a process of manipulation which gave some charming re- 
sults, and which he thus describes : — 

" The following observations are confined to negative paper 
processes divisible into two — the toet and the dry. The solu- 
tions I employ for both these processes are identical, and are as 
follows : — 

Solution of iodide of jjotassium, of the strength of 5 parts of 
iodide to 100 of piu-e water. 

Solution of aceto-nitrate of silver, in the following proportions : 
— 15 parts of nitrate of silver, 20 of glacial acetic acid, 150 of 
distilled water. 

Solution of gallic acid for developing — a satiu'ated solution. 

Solution of hyposulphite of soda, of the strength of 1 part of 
the salt to from 6 to 8 parts of water. 

For both the wet and dry process I iodize my paper as fol- 
lows : — In a tray containing the above solution I plimge, one by 
one, as many sheets of pajier (twenty, thirty, fifty, &c.) as are 
likely to be required for some time. This is done in two or 
three minutes. I then roll up loosely the whole bimdle of sheets 
while in the bath ; and picking up the roll by the ends, ch'op it 
into a cylindrical glass vessel with a foot to it ; and pour the 
solution therein (enough to cover the roU completely) ; in case it 
should float up above the surface of the solution, a little piece 
of glass may be pushed down to rest across the roll of paper and 

MR. Stewart's process. 219 

prevent its rising. The vessel with the roll of paper is placed 
under the receiver of an air-pump and the air exhausted ; this is 
accomplished in a very few minutes, and the paper may be left 
five or six minutes in the vacuum. Should the glass be too 
high (the paper being in large sheets) to be inserted under the 
pneumatic pump-receiver, a stiff lid lined with India-rubber, 
with a valve in the centre communicating by a tube with a 
common dii'ect-action air-pump may be employed with equal 
success. After the paper is thus soaked in vacuo it is removed, 
and the roll dropped back into the tray with the solution, and 
thus sheet by sheet picked off and hung up to dry, when, as "svith 
all other iodized paper, it will keep for an indefinite time. 

"I cannot say that I fidly imderstand the rationale of the action 
of the air-pump, but several valuable advantages are obtained by 
its use : — 1st, The paper is thoroughly iodized, and with an equa- 
lity throughout that no amount of soaking procures, for no 
two sheets of paper are alike, or even one perfect thi'oughout in 
texture, and air-bulbs are impossible. 2d, The operation is 
accomplished in a qtiarter of an hoiu", which generally occupies 
one, two, or more hoxu'S. 3d, To this do I chiefly attribute the 
fact that my paper is never solarized even in the brightest sun ; 
and that it will bear whatever amoiuit of exposure is necessary 
for the deepest and most impenetrable shadows in the view 
without injuiy to the bright light." 

" Wet Process. — To begin with the %vet process. Having pre- 
pared the above solution of aceto-nitrate of sdver, float a sheet of 
the iodized paper upon the sm-face of this sensitive bath, leaving 
it there for about ten minutes. During this interval, having 
placed the glass or slate of your slider quite level, dip a sheet of 
thick clean white printing (imsized) paj^er in water, and lay it 
on the glass or slate as a wet lining to receive the sensitive 
sheet. An expert manipulator may then, removing the sensi- 
tive sheet from the bath, extend its sensitive side uppei-most on 
this wet paper lining, without allo-\ving any air-bubbles to inter- 
vene ; but it is difficult ; and a very simple and most effectual 
mode of avoiding au'-globules, particulai-ly in handhng very large 
sheets, is as foUows: — Pom' a thin layer of water (just sufficient 
not to flow over the sides) upon the lining paper after you have 
extended it on your glass or slate, and then lay down youi* sen- 
sitive paper gently, and by degrees, and floating, as it were, on 
this layer of water, and when extended take the glass and 
papers between the finger and thumb by an upper corner, to 
prevent their slipping : tilt it gently to allow the interjjosed 
water to flow off by the bottom, which will leave the two sheets 
adhering closely and perfectly, without the slightest chance of 


air-bubbles ; it may then be left for a minute or two standing 
ixpright in tbe same position, to allow every drop of water to 
escape ; so that when laid flat again, or placed in the slider, none 
may return back again and stain tbe paper. Of course tbe 
sensitire side of tbe sheet is thus left exposed to the uninter- 
rupted action of the lens, no protecting plate of glass being 
interposed ; and even in this dry and warm climate, I find the 
humidity and the attendant sensitiveness preserved for a couple 
of hours. 

'• Dry Process, — In preparing sheets for use when cZri/ for tra- 
velling, &c., I have discarded the use of previously waxed paper, 
thus getting rid of a troublesome operation, and proceed as fol- 
lows : — Taking a sheet of my iodized paper, in place of floatiag 
it (as for the wet process) on the sensitive bath, I plunge it faMy 
into the bath, where it is left to soak for five or six minutes ; 
then removing it, wash it for about twenty minutes in a bath, 
or even two of distilled water, to remove the excess of niti-ate of 
silver, and then hang it up to dry (in lieu of drying it Avith 
blotting-paper.) Paper thus prepared possesses a greater degree 
of sensitiveness than waxed paper, and preserves its sensitive- 
ness, not so long as waxed paper, but sufficiently long for all 
practical pui'poses, say tliirty hour.s, and even more. The Eng- 
lish manufactiu'ed paper is far superior for this purjDose to the 
French. To develope these views a few drops of nitrate of silver 
ai"e requii-ed in the gallic acid bath, and they are finely fixed and 
waxed as usual." 

It will be apparent to the carefid reader, that all the processes 
given, are in all essential particulars the same. To a few simple 
alterations in the manipiilatory details are due all the variations 
in sensibility, and in the general eifect of the residting pictiu-e. 

The main principles ai-e : — 

1st. To iodize the paper — that is, to secure a uniform coating 
of iodide of silver over every part of the surface of the paper, 
and an entii-e absence of either the alkaline or the metallic 

2nd. To have an excess of nitrate of silver spread over the 
iodide a short time previously to using the paper ; and if a high 
degree of sensibility is requu-ed, the combination of such an 
organic decomposing agent as gallic acid. 

In all the photographs obtained by this process, the impres- 
sions from gi-een leaves are very imperfect. Tliis is only to be 
obviated by adopting the advice of Herschel, and substituting 
the bromide for the iodide of silver. The following remarks are 
so much to the point, that I have transferred them from the 
Journal of the Photographic Society : — 

ME. Stewart's process. 221 

" I hare read, " says Sir J. F. W. Herschel," with considerable 
interest the remarks of Sir W. J. Newton, On Photography in, 
its Artistic view, d-c, conimnnicated to the Photographic Society, 
and by them printed in the Journal of their Society (Xo. 1). 
These remai'ks are in perfect consonance with my own impres- 
sions as to the absence, in the veiy best photographic landscape 
I have seen, of a true artistic representation of the relative in- 
tensities of light and shade, the consequence of which is usually 
a most painfid want of keeping ; — a straggle to come forward of 
parts which natiu'e s\;ppresses, and a want of working ov.t, in 
features which, to the eye, are palpably distinct. 

" Sii' W. J. Newton strikes with the true eye of the painter 
on the more prominent evil of the whole case ; he sa}^ (p. 6), 
' Wondei-fid as the powei-s of the camera are, we have not yet 
attained that degree of perfection as to represent faithfully the 
effect of colours, and consequently of light and shade. For in- 
stance, a bright red or yellow, which woidd act as a light in 
natirre, is always represented as a dark in the camera, and the 
same with green. Blue, on the contrary, is always lighter. 
Hence the impossibdity of representing the true efiect of nature, 
or of a pictui-e, by means of photography.' 

" No one can have viewed the exquisite pictures of M. Eeg- 
naidt or Mr. Stewart, ^\-ithout feeliug that vegetation is unduly 
black and wanting in artistic production. No one who has 
studied colours, not as an artist, but as a photologist, can for a 
moment be ignorant of its cause. The red and yellow rays, and 
especially the former, xchich form so large a portion of vegetable 
greens, are suppressed. They affect not the materials at present 
used in the photogi^aphic art in its highest development. 

" One word suffices for the key of the difficulty — Iodint:. It is 
to the practically exclusive use of this element that the whole 
evil complained of (most justly) is attributable. T have shown 
(see my papers, Phil. Trans. 1840, 1842, Articles 129, 217, and 
' On the Action of the Rays of the Solar Spectrum on the Da- 
guerreotype plate,' Load. Ed. and Dv.hl. Phil. Journal, 184.3, 
Art. xix.) that iodized silver is insensible, or nearly so, to the 
red and orange rays — that its range of sensibility begins, with 
astonishing abruptness, beyond the medium yellow and within 
the blue region — is powerful at the indigo, and extends fai- into 
rays which have absolutely no effect in producing vision. No 
wonder then that iodine produces pictm-es imsatisfactory to the 
artistic eye. Iodine then mxist be thl■o^^^l overboard or Hmited 
in its use, coute qui coute (and the sacrifice is a formidable one), 
if photogi-aphy shaU ever satisfy the desires of the artists. 

" What then are we to have recom-se to ? Bromixe. A new 


photograpliy has to be created, of wliicli bromine is tlie basis. 
This I have proved in. my experiments on this substance {Phil. 
Trans. 1840, Art. 77 ; also Art. xix. Lond. Ed. d-c. Journal, 
above cited). The action of every luminous ray, so far as can 
be traced, is equable throughout the spectiiim ; but the I'ays 
beyond the luminous ones act powerfully, and these must be eli- 
minated. A glass screen, with a very slight yellow tinge applied 
close to the focal picture, oi-, still better, a glass cell, with opti- 
cally true surfaces, containing a weak sokition of sulphate of qui- 
nine, according to the recent results of Prof. Stokes, will effec- 
tually cut oif these, and reduce the action of the rays within the 
limits which ai"t recognizes. I believe M. Becquerel has used 
the latter liquid with a similar view. I will only add, that it 
were much to be wished that artists would study the siJectrum 
and its habitudes in relation to theii* pigments." 

Section II. — Calotype Process on Gelatine or Albumen. 

The use of organic matter in facilitating the change of the 
silver salts very early engaged the attention of Sir John Herschel ; 
and from time to time, following his sxiggestions, others have 
employed various organic mattei-s, albumen and gelatine being 
the favouiite substances. These have been principally used for 
the pm-j)Ose of spreading photogra^ihic preparations on glass, 
which we shall have particularly to describe : at the same time, 
they are stated to have been employed with much advantage 
on paper by some photographists. For the negative pictm-es, 
Gustave Le Gray gives us the following directions and parti- 
cular information : — 

First Operation. — Dissolve three hundred grains of isinglass 
in one pint and three quarters of distilled water (for this purpose 
use a water bath). 

Take one-half of this preparation while warm, and add to it 
as under : — 

Iodide of potassium 200 grains. 

Bromide of ditto 60 „ 

Chloride of sodium 34 „ 

Let these salts be well dissolved, then filter the solution through 
a piece of linen, put it, still warm, in a large dish, and plunge 
in your paper completely, leaf by leaf, one on the other, taking 
care to prevent the air-bubbles fi-om adhering to the paper. 

Put about twenty leaves at a time into the dish, then turn 
the whole, those at the top to the bottom, then take them out 


one by one, and Lang them by one comer vrixh a jiin bent like 
the letter S, to dry spontaneously. 

When hung up, attach to the opposite comer a piece of 
bibulous paper, which vnR facilitate the drying. 

WTien the piper is dry cut it the .size required, and preserve 
it in a folio for use ; this paper may be made in the day-time, as 
it is not sensitive to light in this state. 

The bromide does not, in this case, act as an accelerator, as it 
does on the silver plates of the daguerreotype, because, instead 
of quickening, it retards the operation a little ; its action is to 
preserve from the gallic acid the white of the paper, which 
would blacken more rapidly if you employed the iodide of 
potassium alone. 

Second Operation. — Prepare, by the light of a taper, the fol- 
lowing solution in a stoppered bottle : — Distilled water, 6 fluid 
oiinces; ciystallized nitrate of silver, 250 grains. 

When the nitrate is dissolved, add 1 ounce of crystallizable 
acetic acid : be careful to exclude this bottle from the light, by 
covering it with bhick paper. This solution will keep good until 
the whole is used. 

When you wish to operate, pour the solution upon a porcelain 
or glass slab, sun-ounded with a glass or paper border to keep 
the liqidd fr-om running off. I usually take the solution out 
of the bottle by means of a pipette, so as to prevent the distri- 
bution of any pellicle of dust or other impuiity over the glass 

Take a sheet of the iodized paper by two of the comers, 
holding them perpendicularly, and gently lower the middle of 
the paper upon the centre of the slab ; gradually depress until 
the sheet is equally spread j repeat this operation several times 
tmtil the air-bubbles disappear ; take also the precaution to keep 
the upper side of the paper dry. 

In order to prevent the fingers from spotting the paper, pass 
a bone paper knife under the comer of the sheet, to lift it from 
the slab between that and the thumb. 

Let the sheet remain upon ths slab until the fomiation of the 
chloro-bromo-iodide of silver is perfect. 

This may be known by the disappeai-ance of the violet colour 
which the back of the paper at fii^st presented ; it must not be 
left longer, otherwise it would lose its sensitiveness. 

The time required to effect this chemical change is from one 
to five mi nutes, depending upon the quahty of the paper. 

Spread upon a glass, fitted to the fi-ame of the camera, a piece 
of white paper well soaked in water ; upon this place the pre- 
pared sheet, the .sensitive side upwards. 


Tlie paper wliich you place imdei'neath must be free from 
spots of ii'on and otlier impm-ities. 

It is also necessary to mark tlie side of the glass "syhicli ouglit 
to be at the bottom of the camera, and to keep it ahyays in- 
clined in that dii'ection when the papers are applied ; if this 
precaution is neglected, the liquid collected at the bottom, in 
falling oyer the prepared paper, would not fail to produce spots. 
The paper thus applied to the glass "vnll remain there for an 
hour -without falling off, and can be placed within that time in 
the camera. 

When I am going to take a proof at a distance, I moisten the 
sheet of lining paper with a thick solution of gum ai-abic, and 
can thus preserye for a longer time its humidity and adhesion. I 
can also in this case make use of two glasses between which the 
paper is placed, according to the dii-ection of M. Blanquai-t Eyer- 
ard ; but it is necessaiy to take great care that the plates of glass 
are perfectly clean, and to haye them re-polished if scratched. 

I employ for this pui'pose blotting-paper to clean them, as 
well as my plates : it is much superior to linen, and absorbs 
liquids and impm-ities that adhere to it. I neyer spare the 
blotting-paper, for I would rather use a leaf too much than be 
uncertain about the cleanness of my glass. 

When fhe sheet of lining paper adheres well to the glass, it 
should not be remoyed, but only moistened afresh with water, 
after which you may apply another sheet of the sensitiye paper. 

In preparing seyeral sheets of the sensitiye paper at a time, it 
is not necessary to wash the slab for each sheet ; you need only 
draw oyer it a piece of white paper to i-emoye any dust or pellicle 

When yom- operations are finished, you may pom- back the 
aceto-nitrate of silyer into a bottle, and reserye it for another 

The necessity of employing M. Le Gray's papers in a wet state 
is their most objectionable quality, but certainly the results ob- 
tained by strict attention to his directions are often exceedingly 
beautiful. For deyeloping the image the following is recom- 
mended, which does not, howeyer, differ essentially fi*om the 
deyeloping processes afready described. 

Make about a pint bottle of satimited solution of g-allic acid, 
haying acid in excess, and using distilled water ; decant a por- 
tion into a smaller bottle for general iLse, and fill up the other 
bottle ; you will thus always haye a clear satiu-ated solution. 

Pour upon a slab of glass, kept horizontal, a Little of this 
liquid, spreading it equally with a slip of paper, then apply the 
paper which has been exposed in the same manner as described 


for the negative paper, being careful to keep the back cliy. 
Watch its development, which is easily observed thi-ough the 
back of the paper ; you may leave it thus as long as the back of 
the image does not begin to spot. 

When it is rendered veiy \igorous, remove it quickly to 
another clean slab, and well wash it in several waters, occa- 
sionally turning it, and gently passing the finger over the back; 
by this means you remove any ciystals of gallic acid which 
might spot the picture. 

The appeai-ance of the image at the end of this process will 
enable you to judge if it was exposed in the camera the proper 

If it becomes z, blueish grey all over, the paper has been ex- 
posed too long ; if the strongest lights in the object, which 
should be very black in the negative, are not deeper than the 
half-tints, it has stiU been too long exposed; if, on the contrary, 
it has been exposed too short a time, the lights ai'e but slightly 
marked in black. 

If the time has been just right, you will obtain a proof 
which will exliibit well-defined contrasts of black and white, and 
the Kght pai-ts will be very ti-anspai-ent. The operation is 
sometimes accelerated by heating the galHc acid, and by this 
process the dark parts of the picture are rendered very black. 

To fix these negative proofe, a very strong solution of hypo- 
sulphite of soda, — about 1 ounce of the hyposulphite of soda to 8 
fluid ounces of water, — is employed, and the picture is allowed to 
remain in it untU every trace of yellowness is removed from the 

The VLse of albumen on paper has not been extensive, nor do 
I conceive that it offers any peculiar advantages. The best 
mode of proceeding is to beat the white of eggs into a froth ; 
then set the fluid aside, at rest, and, when perfectly cleai', make 
with it the following solution : — 

White of Eggs, 2 fluid ounces and a half. 
Iodide of Potassium . . .56 grains. 
Bromide of Potassium . . .15^ „ 
Chloride of Sodium ... 4 „ 

Pour the solution into a dish placed horizontally, taking care 
that the froth has entirely disappeared ; then take the paper 
that you have chosen, and wet it on one side only, beginning at 
the edge of the dish which is nearest to you, and the largest side 
of the sheet, placing the right angle on the liquid, and inclining 
it towards you ; advance it in such a manner as to exercise a 
pressm-e which will remove the au-bubbles. Place before you a 


liglit, SO as to be able to perceive tbe bubbles, and to push 
tliem out if tliey remain. 

Let tlie leaf imbibe for a minute at most, without touching it ; 
then take it up gently, but at once, with a very regular move- 
ment, and hang it up by the corner to diy. 

You prepare thus as many leaves as you wish in the same 
bath, taking care that there is always about a qxiarter of an inch 
in depth of the solution in the dish; then place your sheets 
(thus prepared and dried) one on the other between two leaves 
of white paper, and pass over them several times a very hot iron, 
taking out a leaf each time ; you will thus render the albumen 

The iron should be as hot as it can be without scorching the 

Then use this negative paper exactly like the first paper 
named ; only great attention must be obsei-ved that the im- 
mersion in the aceto-nitrate bath is instantaneous, and that 
the air-bubbles are immediately di'iven out ; for every time you 
stop you will make stains on the paper. It is also necessary to 
warm moderately the gallic acid. 

One of the best services rendered by the albumen to photo- 
graphy is, without doubt, its application to the preparation of the 
positive paper, to which it gives a brilliancy and vigom- difficidt 
to obtain by any other method. It is prepared thus : — 

Take white of eggs, to which add the fifth part by volume of 
saturated solution of chloride of sodium ; then beat it into a 
frotli, and decant the clear liquid after it has settled for one 

With this the paper is first washed, and then a strong solution 
of nitrate of silver applied. 

The following is the process adopted by M. Blanquart 
Everard : — 

Method of i^reparing i^aper with albumen, so that it may he 
employed dry. — The paper prepared by means of albumen pos- 
sesses properties analogous to those prepared by means of serum, 
but in a much less degree ; the former, like the latter, may be 
kept for an indefinite time after its preparation with the iodide 
of potassium, but after having been submitted to the action of 
the aceto-nitrate of silver, it "wt.11 not keep good beyond the next 
day. The imi^ressions obtained by means of the following pre- 
pax-ation are adnm-able : though not so well-defined as those on 
glass, yet they are more beautiful, as the outline is less harsh, 
and they possess more harmony and softness. It must not be 
forgotten that the preparations "with albumen change with 
comparative slowness. 


Beat into a froth the whites of eggs, to which a satm-ated 
sohition of iodide of potassium and bromide of potassiiun Las 
been added in the j^roportion of thii-ty di'ops of the former and 
two drops of the latter for the white of each egg ; let the mix- 
ture stand until the froth returns to a liquid state, filter thi'ough 
clear muslin, and collect the albtimen in a large flat vessel. On 
this lay the paper to be prepared, and allow it to remain there 
some miniites. When it has imbibed the albumen, lift it up by 
one of its coniers ; let it it di-ain, and lastly dry, by suspending 
it with pins to a hne or cord across the room. The subsequent 
}3reparation with the aceto-nitrate of silver is in eveiy i-espect 
similar to that for the ordinaiy Calot}q;je paper; care being 
taken not to dry it between the two folds of blotting-paper 
until it has become perfectly transparent. The exposure of the 
pre^iared paper to the light in the camera is done in the same 
way, and the same treatment with gallic acid is followed: it 
will, however, be foimd that the time required for exposure 
"will generally be four or five minutes. 

Preparation of albuminous paper for receiving a positive image. 
— The positive paper prepai'ed with albumen gives impressions 
somewhat shining, but of a very rich tone, well defined, and of 
perfect transparency ; it is prepared in the following manner : — 
To any quantity of white of eggs add 25 per cent, by weight of 
water, saturated with cliloride of sodium ; beat into a froth, and 
filter as in the previous operation — only in this case leave the 
paper in contact with the albumen for half a minute ; hang it 
ujj to dry, which it usually does in six to eight minutes; then 
lay it on a vessel containing a solution of lb parts of nitrate of 
silver in 100 parts of water. Leave the paper on the solution 
for at least six minutes, then place it on a plate to dry. 

The serum of milk has also been employed on paper as a 
quickening agent, and some of the French authorities speak 
highly of it ; but I am not enabled, from my own experience, to 
speak of its advantages. 

Section III. — Calotype Process on Waxed Paper. 

The most successful operators with waxed paper have been 
M. Le Gray on the Continent, and Mr. Fenton in England. In 
a work lately published by Le Gray, he has entered into the 
question of the physical agencies which are active in producing 
the chemical changes on the various preparations employed. 
Throughout the essay, he evidently labours imder an entii'e 


misconception of tlie wliole of the phenomena, curiously enough 
giving a false interpretation to every fact His manipulatory 
details are very pei-fect, but his scientific explanations are only 
so many soiirces of error. 

First Process : To Wax the Paper,— This process divides itself 
into several parts, waxing the jxiper being the first. For this pur- 
pose he takes the paper prepared by Lacroix d'Angouleme, or 
that of Canson brothers of Annouay. A large plate of silvered 
copper, such as is employed for the daguerreotype, is obtained 
and placed upon a tripod, with a lamp underneath it, or upon a 
water-bath. The sheet of paper is spread upon the silver plate, 
and a piece of pui-e white wax is passed to and 6'o upon it until, 
being melted by the heat, it is seen that the paper has unifonnly 
absorbed the melted wax. When this has thoroughly taken 
place, the paper is to be placed between some folds of blotting- 
paper, and then an iron, moderately hot, being passed over it, 
the bibulous paper removes any excess of wax, and we obtain a 
paper of perfect transparency. 

Second Process; To Prepare the Negative Paper. — In a 
vessel of porcelain or earthenware capable of holding 5 pints and 
a quarter of distilled water, put about 4000 gTains of rice, and 
allow them to steep until the gi'ains are but slightly broken, so 
that the water contains only the glutinous portion. In a little 
less than a quart of the rice solution thus obtained, dissolve : — 

Sugar of Milk 620 grains. 

Iodide of Potassium .... 225 „ 

Cyanide of Potassium ... 12 „ 

Fluoride of Potassium ... 7 „ 

The liquid, when filtered, will keep for a long time without 

When you would prepare the paper, some of tliis solution is 
put into a large dish, and the waxed paper, sheet by sheet, is 
plunged into it, one over the other, removing any aii'-bubbles 
which may form. Fifteen or twenty sheets being placed in the 
bath, they are allowed to soak for half an hour, or an hour, ac- 
cording to the thickness of the paper. Tm^ning over the whole 
mass, commence by removing the first sheet immersed, and 
hooking it up by one corner with a pin bent in the shape of the 
letter S, fix it on a line to dry, and remove the drop from the 
lower angle by a little bundle of blotting-paper. M. Le Gray 
then remarks that French and English paper slioidd never be 
mixed in the same bath, but prepared separately, as the "English 
paper contains a free acid, which immediately precipitates an 
iodide of starch in the French papers, and gives to them a violet 


tint." The paper being diy is to be preserved for use in a 

Third Process : To render the Waxed Paper Sensitive. — 
Make a solution of 

Distilled water 2325 gi-ains. 

Ciystallized niti-ate of sUver . . 77^ „ 
and when this is dissolved, add of 

Ciystallized acetic acid -. . . 186 grains. 

Papers prepared with this solution will keep well for a few 
days. M. Le Gray, however, recommends for his waxed paper, 
and for portraits, that the quantity of nitrate of silver be in- 
creased to 15-5 gi'ains, and that it should be used moist. 

The method of preparing these papers is to float upon an 
horizontal plate of glass either of the above solutions, and taking 
a piece of the iodized j^aper, to carefully place it upon the fluid, 
taking gi'eat care that no air-bubbles interpose. The paper must 
remain a short time in contact with this sensitive fluid until 
chemical combination is effected. Four or five minutes are 
requii'ed for some papei-s, and eight or ten seconds are sufficient 
for other kinds. When a violet tint appears the paper should 
be removed. 

For those papers which it is desirable to keep for some time, 
as during a journey, it is recommended that into one vessel of 
porcelain you put about five or six miUiHtres of the strong aceto- 
nitrate above described, and into another some distilled water; 
you plunge completely both sides of the waxed and iodized paper 
in the fii'st fluid, and allow it to remain about foiu- or five 
minutes ; withdi-aw it, and plunge it immediately into the bath 
of distilled water, in which let it soak for not less than four 
minutes. When these papers are carefully di-ied they may be 
l)resei"ved for some time for use, and by lessening the dose of 
nitrate of silver this period may be considerably prolonged. It 
viill of coui-se be understood by all who have followed the pro- 
cesses described up to this point, that the jDapei-s which are pre- 
j)ared for keeping are not those which are the most sensitive ; 
hence it is necessary to expose such a much longer time in the 
camera than those prepared by the stronger solution of silver. 
The more sensitive variety, imder ordinary cii'cumstances of 
light, vnR require an exposiu'e in the camera of about 20 seconds, 
the less sensitive demanding about 10 or 15 minutes, according 
to the cii'cumstances of light. 

Fourth Process : The Development of the Image. — The pic- 
tiu'e is developed by the aid of gallic acid dissolved in distilled 


water. Le Gray finds the folloAving to be tlie best propor- 
tions : — 

Distilled water 40 fluid ozs. 

Gallic acid 60 grains. 

The paper is to be plunged into this solution, and allowed to 
remain until it is fidly developed. The time "svoll vaiy from ten 
minutes to two hoiu's or more, according to the intensity of the 
rays incident on the paper when in the camei'a. The develop- 
ment of the image is much accelerated by the addition of 15 or 
20 ch'ops of the aceto-nitrate of sUver. 

Fifth. Process : Fixing. — It is fomid convenient often, when 
on a journey, to give a temporary fixedness to the pictui-es 
obtained, and to complete the process "with the hyposulphite at 
any time on youi* return home. A wash of 360 grains of bromide 
of potassiiun to two quarts of water is the strength which should 
be employed. The process of fixing with hy]50sulj)hite consists, 
as in other pi'eparations, simply in soaking the paper imtil the 
yellow tint of the iodide has disappeared ; the details are parti- 
cularly given in the chapter on Fixing Photographs. 



In the first di'S'ision of this work, all the details of the original 
processes are given with considerable minuteness, and the vig- 
nette heading to that section exhibits all the ajipai-atvis required 
for even the improved modern practice. 

Section T. — Daguerre's Improved Manipulation. 

The following remarks bj ]\I. Daguerre on polishing and pre- 
paring the plates, from the Comptes Eendus of March 13, 1843, 
shoidd be carefully attended to, as the preliminary process upon 
which the success of every subsequent state depends. 

" Since the publication of my process, I have not been able 
to occupy myself much with it. The investigations to which I 
devoted myself have been in an entirely new dii-ection, and the 
experiments which they reqinred were analogous with the pre- 
ceding ones, only inasmuch as they were made on a metallic 
plate. However, I have lately been so much stmick with the 
\mequal resxdts which the impressions generally present — even 
those of persons who are especially occupied with them — that I 
determined to seek some means of remedying this serious incon- 
venience, which I attribute to two principal causes. 

" The fii'st relates to the operation of polishing, which it is 
physically impossible to effect without leaving on the siu-face 
of the plate traces of the liquid and of the other substances 
used in this operation : the cotton alone which is employed, 
however clean it may be, is sufficient to leave a film of dirt on 
the silver. This first cause constitutes a very gi-eat obstacle to "^ 
the success of the impression, becaxise it retards the photogenic I 
action by preventing the iodine from coming in direct contact / 
with the silver. 

"The second consists in the altemtions of the temperatiu'e of 
the air with wliich the plate is in contact, fr'om the tu-st opera- 
tions to the mercurial operations. It is kno"\\Ti that when a cold 
body is sm'rounded with warmer air it condenses its moistiu'e. 
To this effect must be attributed the difficidty which is expe- 


rienced in operating in a humid medium, especially when we 
come to the mercurial operation, wliich requires, to raise a suit- 
able vapour, a temperatvxre of 122° F. 

" This vapour, which first heats the air contained in the 
apparatus, produces on the metal a dew which weakens the 
image. It is very evident that this humid layer is very injui-ious ; 
since if, for example, the plate, on leaving the camex-a obscui-a, 
be breathed on two or tliree times, the mercurial vapour can no 
longer cause the impression to apj)ear. 

" The water which is condensed, even at the slightest difference 
of temperature between the surface of a body and the surrounding 
air, contains in solution, or in susjoension, a non-volatUe sub- 
stance, which might be called atmospheric dust ; and as soon as 
the equilibrium of temperatui-e is estal Wished between the air 
and the surface of the body, the humid vapour wliich was con- 
densed on it is volatilized, and depositing on it the dust which 
it contains, goes on to be re-saturated in the air with a fresh 
quantity of this impure substance. 

" In order as much as possible to neutralize this efiect, the 
temperature of the plate may be kept higher than that of the 
surrounding air, during each of the operations. But it is im- 
possible to cause tliis hea,t to reach to 122° F., in order for it to 
be of the same temperature as the vapour of mercury, since, if 
the plate be exj^osed to that degree of heat after the operation 
of light in the camera obscura, the image will be altered. 

" I fij'st tried to absorb the humidity of the ail' in the mercu- 
rial box by the usual means, such as lime, &c. ; but these means 
are insufficient, and only complicate the process, without giving 
a good result. Another means which has been proposed con- 
sists in vapourizing the mercury under the pneumatic machine ; 
by this process, truly, the dew on the plate is avoided, but the 
pressiu'e of the air, which is indispensable to the impression, 
is suppressed. The results thus obtained, also, are always 
wanting in purity. 

" The following is the process at which I have stopped, 
because it is very simple, and because it obviates the two incon- 
veniences above mentioned ; that is to say, it frees the silver as 
much as possible from all dirt or dust, and neutralizes the 
humidity produced by the elevation of temperatiu-e in the mer- 
curial box. By the first of these two eflfects it increases the 
joromptitude, and by the second it renders the lights much 
whiter (especially by the application of ]\I. Fizeau's chloride of 
gold) : these two eficcts are always certain. The 2:)romptitude 
given by this process is to that hitherto obtained as 3 to 8 : this 
proportion is accurate. 

daguerre's improved manipulation. 233 

" This process consists in covering the plate, after having 
polished it, with a layer of very pure water, and heating it very 
strongly with a spirit-lamp, and in aftersvards pouring off this 
layer of water in such a manner that its upper part, where the 
dust which it has raised floats, does not touch the plate. 

" It is necessary to have a fi'ame of iron wire of the size of 
the plate, having at one of its angles a handle,- and in the mid- 
dle, on the two opposite sides, two small cramp-irons, to retain 
the plate when it is inclined. After ha\TJig placed this frame 
on a hoi-izontal plane, the plate is placed on it, which is covered 
with a layer of very piu'e water, and putting as much water as 
the surface can retain. The bottom of the plate is afterwards 
veiy strongly heated, and veiy small bubbles are formed at the 
sui'face. By degrees these biibbles become larger, and finally 
disappear ; the heat must be continvied to ebvJlition, and then 
the water must be poiu'ed ofi". The operator should commence 
by placing the lamp under the angle of the fi-ame where the 
handle is ; but, before removing the frame, this angle must be 
very powerftilly heated, and then, by gradually remo\Tng it by 
means of the handle, the water immediately begins to run off. 
It must be done in such a way that the lamp shall follow, under 
the plate, the sheet of water in its progress, and it must be 
only gradually inclined, and just suflicient for the layer of water, 
in retiring, not to lose in thickness ; for, if the water were 
dried up, there would remain small isolated di'ops, which, not 
being able to flow off, would leave on the silver the dust which 
they contain. After that, the plate must not be rubbed : very 
pui-e water does not destroy its polish. — - ,^ 

" This operation should be performed only just before iodizing 
the plate. Whilst it is yet warm, it is placed in the iodizing 
box, and, without allo-sving it to cool, it is submitted to the 
vapour of the accelerating substances. Plates thus prepared 
may be kept one or two days (although the sensibility diminishes 
a little), provided that several plates be placed opposite to one 
another, at a very short distance apart, and careftdly enveloped 
to prevent change of aii- between the plates. 

" The plates cannot be too well polished. It is one of the 
most important points to obtain a fine polish ; but the purity 
often disappears when substances which adhere to the siu'fage 
of the silver are used, — such as the peroxide of iron, which has 
been very generally made use of for giving the last polish. 
This substance, indeed, seems to biu-nish the silver, and to give 
it a more perfect polish ; but this polish is factitious, since it 
does not really exist on the silver, but in fact on a very fine 
layer of oxide of iron. It is for this reason that there is re- 


quired for polishing tliem a substance wliich. does not adliere to 
tlie silver ; pumice, which I recommended at the commencement, 
leaves less residue. 

" As regards the liquid to be employed : in the first operations 
nitric acid of five degrees must be employed, as I stated in the 
first instance ; bvit for the last operations it must be reduced to 
one degree. 

" The polishing with oil and the heating may be suppressed. 

" I take the opportunity afibrded by this communication to 
lay before the Academy the following observations, which I owe 
to experience : — 

" The layer produced by the descending vapoiu's of the iodine 
and of the accelerating substances forms Avith silver a more sen- 
sible compound than is obtained with the ascending vapours. 
I make this observation only to lay down a fact, for it would be 
difficult to employ descending vapours, on account of the dust 
which might fall dm-ing the operation, and from stains. 

" The resistance which light experiences in passing through a 
white glass is well known. This resistance is even greater 
than it appears, and may be attributed not only to the dust 
which is left on the glazing in cleaning it, but also to that 
which is natxu'ally deposited on it. The object-glass of the 
camera obscui'a is certainly in the same case. To ascertain this, 
I put the object-glass in cold water, which I boiled ; I knew 
that it was impossible to remove it without the sides. This 
operation had, therefore, no other object than to raise the tem- 
perature of the glass to 212° F. C, and I then immediately 
poiu-ed on the two sides of the object-glass very piu-e boiling 
water to remove the dust. By operating dii'ectly Avith the 
object-glass, thus cleansed, I still further increased the prompti- 
tude. This means presents too many difficulties to be j)ut in 
practice ; only care should be taken to clean the object-glass 
every day.* 

" The atmospheric dust, which is the scoiu-ge of the photo- 
genic images, is, on the contrary, favourable to images wliich are 
obtained by contact or at a very short distance. To be con- 
vinced of this, we have only to clean the two bodies which we 
wish to put in contact with the boiling water, as T have just in- 
dicated, and to keep them both at the same temperature as the 
air ; there will then be no impression, which evidently proves 
that these images have no relation with the radiation which gives 
photographic images." 

* Professor Stokes has recently confirmed the truth of this by some very 
conclusive experiments. 


Section II. — Polishing the Plate. 

Upon this subject but Httle remains to be added to what is 
stated in DagueiTe's earliest form of manipulation, and the few 
remarks just quoted. 

It is of the utmost importance that a very perfect mirror sur- 
face should be produced, and to ensure the utmost freedom from 
all organic matter during the polishing; the plate-holder repre- 
sented in two positions by e e, in Fig. 63, has been devised. 
The plate-holder is secured to a table by a clamp, and the plate 
to be polished is fixed upon the horizontal svu-face of the plate- 
holder by means of four binding-screws placed at its comers. 
The plate having undergone the preliminaiy rubbing, which, as 
being a comjjaratively coai'se operation, need not be fui-ther de- 
tailed than it is in the earlier section, and having been fixed on 
the holder, the last poHsh is to be given to it. The hand- 
buff, i, in Fig. 63, is to be dusted over with animal charcoal, 
and moistened with a little spirits of ^vine : some opeiutors em- 
ploy tripoli in a state of impalpable powder mixed -vv-ith essential 
oil of lavender. If, however, any essential oil is used, it must 
be ascertained to be quite free from castor oil, — with which it is 
very commonly adulterated, — ^by placing a di'op on a piece of 
paper: if it is a piu-e essential oil, it ■s\-ill, when wai-med, entirely 
evaporate, but if not, a greasy spot will remain. 

In jNI. Claudet's establishment, where, from long experience, 
the best modes of manipulation are introduced, the last b uffin g 
is efi"ected in a somewhat different manner. 

In a box on a roller, to which there is a handle, Fig. 59, is 


placed a long piece of drab-coloured velvet, which can be di"awn 
out and extended, by means of a second roller, upon the per- 
fectly flat table. The fii'st foot or two, for example, is di-a^vn out : 
the plate, which has already received its preliminaiy polishing, is 
placed face downwards, and being pressed close with the fingers, 
a rapid cii-cidar motion is given to it, and in a few minutes it 


receives its highest kistre. As the velvet becomes blackened 
by use it is rolled off, the portion remaining in the box being 
always perfectly clean, and ready for use. The plate is now 
ready for receiving its sensitive coating, and, to avoid the chance 
of the surface touching any other object, M. Claudet adopts 
the simple but most effective mode of pushing it from the buff 
into a spherical wooden bowl, in which the plate rests by its 
four corners in perfect security. 

As the edges of the metallic plates are generally sharp, they 
would often cut the buffs, were that accident not jjrevented by 
a suitable precaution. Fig. 60 re- 
^^=^^>— — presents an apparatus called a plate- 

hender. The surface a is perfectly 
horizontal, and has a steel border near 
the bar h : upon the bar h runs a press 
that carries a steel knife edge so rounded as to be able to bend a 
plate but not to cut it. The silver plate that is to be buffed is 
placed on this appai'atus with an edge close to the back bar, and 
the press is then run along it from end to end, by which means 
the edge of the silver plate is bent downwards in a very slight 
degTee, but sufficient to prevent any cutting action on the buffs. 
All the four edges of each plate are bent in the same manner. 

Section TII. — To Give the Sensitive Surface to the Plate. 

Various compounds, called accelerating liquors, have been in- 
troduced, in all of which we have combinations in various pro- 
portions of either bromine and iodine, or chlorine and iodine, 
and sometimes of the three. These are known by the names of 
Eau Bromee, or Bromine Water, Bromide of Iodine, Redman's 
Sensitive Solution, Himgarian Liquid, and Woolcott's Accelerat- 
ing American Fluid. These accelerating compounds are em- 
ployed after the plate has been subjected to the vapoui- of iodine. 
They all require to be diluted with water until about the colour of 
pale sheriy. The plate is exposed to the influence of the vapour 
which is escaping from the solution used in the same manner as 
■with the iodine, but the colom- to be attained differs according to 
the solution employed. An iodizing box is shown at c. Fig. 63 : 
at the bottom of this some iodine is strewed, and in general it is 
covered with a little sand or a card; — the object of this is to 
avoid an irregular action on any part of the plate : the box being 
adjusted with a cover, the iodine is preserved from evaporation 
and lasts a long time. When the plate has assumed its fine 


straw yellow in the iodine box, it is removed to the action of the 
accelerating agents, liquid or otherwise, as the case may be. The 
following rules will guide the experimenter in using the different 
preparations. If bromide of iodine be used as the accelerating 
agent, the plate should remain over the iodine until it is of a 
pure yellow tint, and over the bi-omine till of a deep rose colour. 
By observing the time of exposure necessary to render a plate 
sensitive, any number of plates may be prepared exactly alike, 
provided that the same quantity of th'e solution, always of an 
uniform strength, be put into the pan. By using a much weaker 
solution a longer exposure is then necessary, but the plate be- 
comes more evenly covered, and there is less danger of having it 
too much or too little acted upon by the accelerator. The same 
remark will apply to other accelerating solutions. If Redman's 
solution, or the Hungarian liquid, a pale yellow and light rose 
will be found most sensitive. As a general rvile, if the yellow 
colour produced by the iodine be pale, the red should be pale 
also; if deep, the red must incline to violet. When several 
plates are to be prepared at one time, the same solution will 
serve for all ; but it seldom answers to preserve the mixtvire for 
any long time ; and its use, after keeping, is one great cause of 
the failures which so annoy amateiu's. The bromine contained 
in these solutions is veiy subtile, and escapes, leaving little else 
but iodine remaining, which Avill, after some time, give a red 
colour to the plate, without rendering it sensitive, entirely dis- 
appointing the expectations of the operator. Eau bromee, or 
bromine water, which is very easily prepared, is extensively used 
on the Continent, and is simple in its use. If a certain quantity 
of an uniform solution be placed in the pan, for each plate pre- 
pared, one observation will suffice to determine the time of ex- 
posui'e; if not, the coloTir must guide the operator, varying 
according to the degree of colour obtained over the iodine : thus, 
if the fii'st colour obtained be a light yellow, the plate should 
attain a full golden tint over the iodine, and may then be retained 
over the bromine until it acquires a rose colour. If iodized of a 
golden yellow, then, in the second operation, it is taken to a pale 
rose, and in the third to a deep rose. If in the first of a full red, 
in the second to a deep red, and lastly to a grey ; if the first to 
a deep red, in the second to a light blue, and in the third, to a 
white, or nearly the absence of all colour. 

Experience, however, must invariably guide the operator, as 
scarcely any two solutions, though professedly the same in cha- 
racter, possess the same properties. 

In a pamphlet published by M. Fizeau, bromine-water is 
recommended to be prepared as follows: — "To prepare a solution 


of bromine, of a fixed proportion and convenient strength to 
operate "witli, I, iu the fii'st place, make a satiu-ated solution of 
bromine in water; this is prepared by putting into a bottle of 
piu-e w-ater a great excess of bromine, agitating strongly for 
some minutes, and before using allo'wing the bromine to sepa- 
rate. Now, a definite quantity of this f:atm-ated water ls to be 
mixed with a definite quantity of plain water, which will give a 
solution of bromine always of the same strength : this mixtui'e 
is conveniently made in the following manner : — The apj)aratus 
necessary is a dropping tube, which is also requii'ed for another 
part of the process, cajDable of holding a small definite quantity, 
and a bottle having a mark to indicate a capacity equal to thii'ty 
times that of the di-opping tube : fill the bottle with pvu-e water 
to the mark, then add, by means of the di'opping tube, the pro- 
per quantity of the satiu'ated solution of bromine. 

" The pui'ity of the water is of some impoi-tance : the foregoing 
proportions refer to the pure distilled water, and it is well known 
that the water of rivers and springs is not pui'e ; but these 
different varieties can be used as if they were absolutely pure 
water by adding a few di-ops of nitric acid till they taste slightly 
acid ; two,or thi-ee drops to the pint is generally sufficient. 

"The liquid produced, which is of a bright yellow coloiir, 
ought to be kept in a well-stopped bottle ; it is the noi'mal 
sokition, and I shall call it simply bromine water, to distinguish 
it from the satiu-ated solution. 

'•' Bromine Box. — The box I employ for subjecting the plate 
to the vapoui' of the bromine water is constructed in the follow- 
ing manner : — It consists of a box lined with a varnish, which is 
not acted on by bromine ; its height is about foui- inches ; the 
other dimensions ai"e regvdated by the size of the plate, which 
ought to be at least half an inch all round, short of the sides of 
the box; it is composed of three separate portions — the cover, 
which is the £i"ame holding the plate, the body of the box, and 
the bottom, upon which is placed the vessel for the bromine; 
this moveable bottom is slightly hollowed, so that the bromine 
vessel may always be placed in exactly the same position." 

Few men have done more for photography than M. Fizeau, and 
in nearly all his siiggestions he has been exceedingly happy : the 
bromine water thus prepared is used with the best effect by our 
most eminent daguerreotype artists. 

Bromide of iodine is best prepared by the method of "SI. de 
Valicoui-s, which is as follows : — " Into a bottle of the capacity 
of about two oimces, pour thu-ty or forty di'ops of bromine, the 
precise quantity not being of importance. Then add, gi-ain by 
grain, as much iodine as the bromine will dissolve till quite 


saturated. Tliis point is ascertained wlien some gi-ains of the 
iodine remain undissolved. Tliey may remain in the bottle, as 
they ■will not interfere with the success of the preparation. 

" The bromide of iodine thus prepared, fi'om its occujiying so 
small a space, can very easily be carried, but in this state it is 
much too concenti-ated to be iLsed. When it is to be employed, 
pour a small quantity, say fifteen di-ops, by means of a th-op- 
piug-tube, into a bottle containing about half an ounce of filtered 
river water. It will easily be understood that the bromide of 
iodine can be iised with a greater or less quantity of water, with- 
out altering the proportion which exists between the bromine 
and iodine." 

Mr. Goddard, on December 12, 1840, published a letter in the 
Literary Gazette on the use of bromide of iodine as an acceler- 
ating agent, but chloride of iodine was fii-st employed by M. Clau- 
det in 18-41, and is prepared by merely placing iodine in an 
atmosphere of chloiine. Chloride of bromine is made by mixing 
two drachms of a sattu'ated solution of bromine with fifteen 
di'ops of strong mm'iatic acid and about nine or ten ovmces of 
water. The Himgarian mixtui'e appears to be a similar com- 
pound to this. 

For the following exceedingly convenient preparations we are 
indebted to Mr. R. J. Bingham, who has for some time, with 
much siTccess, devoted his attention to the improvement of 
photographic processes. The following extracts are fi'om the 
Philosopltical Jfagazine for Octobei", 1846 : — 

"An Improvement in the Dacjuerreotype Process hy the appli- 
cation of soTne new compounds of bromine, cldorine, and iodine, 
vjith lime. — All pei-sons who have practised the dagueiTeotype 
must have remarked that in warm weather a con.siderable depo- 
sition of moistiu'e takes place upon the glass or slate cover used 
to confine the vapoui' in the bromine or accelerating pan. This 
moisture must also necessaiily condense upon the cold metallic 
siirface of the plate dm-ing the time it is exposed to the bromine 
vapour. In fact, I have been informed by a number of profes- 
sional daguerreotypists (and I have experienced the difficulty 
myself), that they were unable to obtain perfect pictures during 
the excessive heat of the late season ; and a veiy clever and 
enterprising operator, who last year made a tour on the Con- 
tinent, and brought home some of the finest proofs I have ever 
seen, entii-ely failed this season in obtaining clear and perfect pic- 
tiu'es, fi'om the constant appearance of a mist or cloud over the 
prepared surfoce. This appeai-s to be caused by the deposition 
of moistm-e u^^on the plate, arising from the water in which the 
bromine is dissolved. To obviate this, some have recommended 


the pan to be kept at a low temperature in a freezing mixture ; 
and M. Daguerre, in a communication to tlie French Academy 
of Sciences, recommends the plate to be heated : but in practice 
both these are found to be unsuccessful. (See Lerebours' Traite 
de Photographie?) 

" It appeared to me, that if we could avoid the use of water 
altogether in the accelerating mixtiire, not only would the diffi- 
culty I have mentioned be avoided, but a much more sensitive 
sui'face would be obtained on the plate. With this view T 
endeavoured to combine bromine with lime, so as to form a 
compound analogous to bleaching powder. In this I was suc- 
cessful, and find that bromine, chloride of iodine, and iodine, 
may be united with lime, forming compounds having properties 
similar to the so-called chloride of lime. 

" The bromide of lime* may be produced by allowing bromine 
vapour to act upon hych-ate of lime for some hours : the most 
convenient method of doing this is to place some of the hydrate 
at the bottom of a flask, and then put some bromine into a glass 
capsule supported a little above the lime. As heat is developed 
dimng the combination, it is better to place the lower jiart of 
the flask in water at the temperature of about 50° Fah. : the 
lime gradually assumes a beautiful scarlet coloiu", and acquires 
an appearance very similar to that of the red iodide of mercury. 
The chloro-iodide of lime may be formed in the same manner : 
it has a deep brown colour. Both these compoimds, when the 
vapour arising from them is not too intense, have an odour 
analogous to that of bleaching powder, and quite distinguishable 
from chlorine, bromine, or iodine alone. 

" Those daguerreotypists who use chlorine in combination 
with bromine, as in Woolcott's American mixtui^e, or M. 
Guerin's Hungarian solution, which is a compound of bromine, 
chlorine, and iodine, may obtain similar substances in the solid 
state, which may be used with great advantage. By passing- 
chlorine over bromine, and condensing the vapours into a liquid, 
and then allowing the vapour of this to act upon lime, a sohd 
may be obtained having all the j^roperties of the American 
accelerator ; or by combining the chloro-iodide of lime with a 
little of the bromide, a mixture similar to that of M. Guerin's 
may be produced : but I greatly prefer, and would recommend, 

* " I call this substance bromide of lime, although there is a diificulty as to 
the composition of bleacliing powder, and which would also apply to the com- 
pounds I describe. Some chemists regard the chloride of lime to be a compound 
of lime, water, and chlorine. Balard thinks it is a mixture of hypochlorite of 
lime and chloride of calcium ; and the view of Millou and Prof. Graham is, that 
it is a peroxide of lime, in which one equivalent of oxygen is replaced by one 
of chlorine." 


tlie piire bromide of lime, it being, as I believe, tlie quickest 
accelerating substance at present kno-vru. Ey slightly colouring 
the plate with the chloro-iodide, and then exposing it for a pro- 
per time over the liromide, proofs may be obtained in a fraction 
of a second, even late in the afternoon. A yellow coloiu- should 
be given by the use of the fii-st substance; and the proper time 
over the bromide is readily obtained by one or two trials.* 
With about a drachm of the substance in a shallow pan, I give 
the plate ten seconds the whole of the first day of using the pre- 
paration, and add about thi-ee seconds for eveiy succeeding one. 
The compomid shoidd be evenly strewed over the bottom of the 
pan, and will last, with care, about a fortnight. 

" The gi'eat advantage of this compound is, that it may be 
used continuously for a fortnight without renewal ; and, unlike 
bromine water, its action is unafiected by the ordinary changes 
of temperatm-e." 

The advantages of a dry material are so great, that the bro- 
mide of lime is now commonly used. 

By the emplo}Tnent of these agents a sensitive coating is pro- 
duced, upon which actinic changes are almost instantaneously 
made. The modes of proceeding to prepare the plates are 
similar to those already named. 

The time necessary for the jilate to be exposed to the action 
of the bromine water, if it be used, must be determined by expe- 
riment, for it will vaiy according to the size of the box and the 
quantity of liquid used. It is ordinarily between thii-ty and 
sixty seconds, the time varying with the temperatui'e of the 
atmosphere: when once determined, it will be constant with 
the same box, the same strength of solution, and the same 

The method of coating the plate with bromine from the water 
which is most approved is as follows : — Place a pan in a properly 
prepared box, fill a pipette with bromine water, and pour it 
careftilly from this into the pan, then close the vessel with a glass 
plate : the liquid must cover evenly the bottom of the pan ; 
if not level, it must be adjusted: the level will be easily seen 
through the glass slide. When everything is thus aiTanged, the 
plate, previously iodized, is to be placed in its fi-ame over the 
pan, the slide withdi-awn, and the necessary time counted ; after 

* " It is better to count time both over the iodine and the bromide of lime : 
the exposure of the plate to the iodine, after it has received its proportion of 
bromine, should be one-third of the time it took to give it the first coating of 
iodine. We have found that if less iodine than this be allowed to the plate it 
will not take up so much mercury, neither will the picture produced be so bold 
and distinct." 


this has elapsed, the slide should be shut, and the plate imme- 
diately placed in the dark box of the camera. 

For a second operation, this bromine water must be thrown 
away, and a fresh quantity used. The bottle containing the 
bromine water should be kept away from the direct light of the 
sun, and care should be taken that no organic matter fall into 
the bottle, such as grease, chips of cork, &c. These enter into 
new combinations with the bromine, and lead to error as to the 
amount in solution. 

Daguerre himself introduced some very considerable improve- 
ments in the process of iodizing. He avoided the use of metal 
strips, and gave some curious experiments on the action of 
edges, grooves, &c., in determining the deposition of vapouj'. 
M. Daguerre stated that, but for the difficulty of fixing them, 
the bands might be very much reduced in size ; for it is suffi- 
cient for them to produce their effect that there be a solution 
of continuity between them ; and this is proved by the fact that 
nearly the same result is obtained by engraving at the -gth of an 
inch from the edge of the plate a line deep enoiigh to reach the 
copper. The objections to this are, that during the polishing 
process the engraved line is filled witli dust, and it retains water, 
which sometimes occasions stains. He then proposed, as a very 
great simplification of this process, that the plate should be laid 
flat in a shallow box containing two gTOoves, one to receive the 
plate, and the other a board saturated with iodine. Around the 
plate he places a border of either powdered starch or lime, and 
the iodine descends from the board to the tablet. The starch 
or lime absorbs the iodine with avidity, and thus prevents its 
attacking the edges of the silver, and the vapour is diffused with 
perfect evenness over it. Another advantage is, that the satu- 
rated board may be used for several days in succession, "without 
being renovated. 

M. Seguier somewhat modified even this process. A box of 
hardwood, varnished internally with giim lac, contains a lump 
of soft wood, furnished with a card of cotton sprinkled with 
iodine. Upon this is placed a plate covered with card-board on 
each of its faces. One of these card-boards furnishes, by radia- 
tion, to the metal the vapour of iodine, while the other returns 
to the cotton that which it had lost. It suffices to turn the 
plate from time to time, in order that the operation may go on 
with equal rapidity. A plate of glass is placed upon the upper 
card-board, where it is not operated on. The plate is sustained 
a little above the charged cotton by frames of hardwood var- 
nished with gum lac. By increasing the distance between the 
cotton and the plate, or the contrary, we are enabled to suit the 


arrangement to the tempei-ature of the season, and thus always 
operate with facihty and promptituda M. Seguier also states, 
that a single scouring with tripoli, moistened with acidulated 
water, is sufficient to cleanse the plates thoroughly, thus doing 
away with the tedious process of scoui'ing with oil, and after- 
wards the operation of heating the tablet over a spiiit lamp. 
M. Soliel has proposed the use of the chloride of silver to de- 
termine the time required to produce a good impression on the 
iodized plate in the cameiu. His method is to fix at the bottom 
of a tube, blackened within, a piece of cai"d, on which cliloride 
of silver, mixed with gum or dextrine, is spread. The tube thus 
disposed is tiu-ned towards the object of which we wish to take 
the image, and the time that the chloride of silver takes to be- 
come of a grayish slate colour, Avill be the time required for the 
radiations in the camera to produce a good eflect on the iodated 

These remarks have been introduced as supplementary to the 
generally approved modes, as they are suggestive in themselves 
of still frnther improvements. 

Section IY. — To Develope the Image formed on the Plate. 

The plate, prepared by one of the methods directed, has been 
placed in the camera, and the image impressed upon it — atten- 
tion being given to the points especially alluded to in the chap- 
ter " General Remarks on the iise of the Camera Obscura." 

The image is developed on the daguerreotype plate, as has been 
already described, by the use of mercimal vapour. In the ori- 
ginal process (Fig. 10), one form of a mercurial vapour-box is 
given ; and Fig. 63, d, represents another. 

It matters little in what manner the plate is placed in the 
mercurial bath ; the mercmy should be volatilized very slowly, 
and the image allowed to have its fiill development before it is 
removed from the box. Cai-e should be taken that the operator 
avoids as much as possible contact with the mercurial vapour, 
since continued exposure to its influence might lead to serious 

M. Claudet has adopted a most admirable arrangement in this 
respect, as is shown in the woodcut on the following page. 

Fig. GO represents a small dark chamber fixed outside the 
apartment in which the operations are carried on, but opening 
iuto it by means of sliding glass doors. On either side of the 
chamber are placed pieces of yellow glass, through which, on 



opening the shutters bj which thej are covered, a sufficient 
quantity of light is admitted to serve any useful pm^pose, with- 
out in any way interfering with the sensitive suifaces of the 
plates. Within this chamber are placed two mercuiy boxes, each 

containing a small quantity of that metal. One of these is shown 
in section. Each box is placed over a water bath, .supplied by 
means of a pipe with water from a cistern above, and a small 
sand bath is placed between the mercmy box and the water 
bath. By means of the gas-bui'ner beneath the box, the water 
is heated, the mercury volatilized slowly and deposited on the 
plates, which are fixed on the grooves shown on the sides of 
the box in section. The windows being closed, any mercurial 
vapoui's which may escape fi-om the box may pass out into the 
air through proper ventilators, and the operator is thus protected 
from the injui'ious efiects of the merciu'j'. 

fixing the daguerreotype image. 245 

Section Y. — Fixing the Daguerreotype Image. 

It has already been stated that the solution of hyposulphite 
of soda is the most effective agent for removing all the unchanged 
iodide of silver, after the application of, and the development 
of the image by, the mercurial vapour. 

This being effected, greater permanence is given by the appli- 
cation of a solution of gold. 

The process as described by JM. Fizea'u, to whom we are in- 
debted for its introduction, is as follows : — 

" Dissolve eight gi^ains of chloride of gold in sixteen ounces 
of water, and thii-ty-two grains of hyposulphite of soda in foiu' 
ounces of water : pour the solution of gold into that of the soda, 
a little by Kttle, agitating between each addition. The mixture, 
at first slightly yellow, becomes afterwards perfectly limpid. 
This liquid now contains a double hyposulphite of soda and gold. 
'' To use this salt of gold, the sxuface of the plate should be per- 
fectly free from any foreign substance, especially dust ; conse- 
quently it ought to he washed with some precautions which might 
be neglected if it was to be finished l)y the ordinaiy mode of washing. 
" The following manner generally succeeds the best : the plate 
being yet iodized, and perfectly free from grease on its two sur- 
faces and sides, should have some drops of alcohol poured on the 
iodized siu-face ; when the alcohol has wetted all the siu-face, 
plunge the plate into a basin of water, and after that into a solu- 
tion of hy^Dosulj^hite of soda. 

" This solution ought to be changed for each experiment, and 
to consist of about one part of the salt to fifteen of* the water : 
the rest of the vrashing/'is done in the ordinaiy way, only taking 
care that the water should be as free as possible from dust. 

"The use of the alcohol is simply to make the 
water adhere perfectly aU over the sm-face of the 
plate, and prevent it from quitting the sides at 
each separate immersion, which would infallibly 
produce stains. 

When a pictm-e has been washed, with these 

precautions, the treatment -ndth the salt of gold is 

very simple. It is sufiicient to place the plate on 

Qj^ ■ ' 2^^ a support, fig. 61, or fig. 63, g, and pour upon its 

'^'J^Iinsil^"' sm-face a sufficient quantity of the salt of gold 

61. that it may be entirely covered, and heat it with 

a strong spirit-lamp ; the pictm-e will be seen to 

brighten, and become in a minute or two of great force. When 

this effect is produced, the liquid should be pom-ed off and the 

plate washed and chied. 



" In tliis operation the silver is dissolved, and the gold pre- 
cipitated upon the silver and merciuy, but wdtli very different 
results : in effect, the sUver, which, by its reflection, forms the 
shades of the picture, is in some way darkened by the thin film 
of gold which covers it, from which results a strengthening of 
all the dark jDarts. The mercury, on the contrary, wliich, in the 
state of an infinite number of small globules, forms the lights, is 
augTnented in its solidity and brightness by its union with the 
gold, from which results a great degree of permanency, and a 
remarkable inci-ease in the lights of the picture." 

The plates are then washed by means of an arrangement of 
this order. The apparatus represented in fig. 62 may be employed, 
a is a vessel sufl3.ciently large to take the 
plate, and not more than half an inch 
Avide : this is filled with distilled water, 
which is heated by means of a spirit-lamp ; 
6 is a stand supporting the trough, and c 
a holder for the plate. After the plate 
has been immersed for a few minutes, 
it is to be dra^Ti out slowly, and by 
blowing on it the water is I'emoved, and 
the warm metal rapidly dried. Such are 
the principal processes which have been 
go adopted in the daguerreotype manipu- 

lation. Other modes for giving perma- 
nency to the dagueiTean image have been adoj^ted, but none of 
them have been so thoroughly successful as those. 

It appears advantageous to quote a few of the modified forms 
of proceeding for fixing these pictures, when obtained, which 
have from time to time been recommended. 

M. Preschot, in a letter to M. Arago, remarks — 
" In one of the sittings of last month you mentioned a process 
for fixing photogenic images on metal. Knomng, as I do, the 
interest you take in the beautiful discoveiy of the daguerreotype, 
I hope you will excuse the liberty I take in troulaling you with 
results which I obtained in experiments made a few months ago. 
" Photogenic images, obtained by M. Daguerre's process, may 
be fixed by treating them with a solution of hydi-osLdphite of 
ammonia. For this purpose, a concentrated solution of this 
fluid is mixed yvith three or fom* volumes of pui*e water, wliich 
is poiu-ed into a flat vessel, in sufiicient qviantity that the jjlate 
may be steeped in it horizontally, and just covered with the 
fluid. When, by the action of the fluid, the tints of the di'awing 
are sufiiciently changed, which occurs in less than a minute, the 
plate is to be withch-awn, and put into a flat vessel containing 


water : it is afterwards taken out and di'ied. By this process 
the polished parts of the metal are tinged gray by the sulphui-et, 
and the amalgamated parts are not attacked, or, at least, but 
very little. The tints may be varied by the concentration of 
the fluid or the duration of the immersion ; however, too long 
an action turns the lights yellow. PhotogTaphic images, treated 
in this manner, bear iiibbing with the finger wdthout losing any 
of their details. " 

M. Choiselat proposed a plan which "has been rarely acted 
upon, but which is well deser\Tng of attention. 

Chloride, and particularly iodide of silver, dissolved in hypo- 
suljihite of soda, may be advantageously employed for fixing the 
images of the daguerreotyj)e. Steeped in these solutions, they 
are, imder the electro- chemical influence exerted by the copper 
on the dissolved silver, coated with a film of silver, and thus 
become ineflfaceable. 

Instead of the hyposulphite, a mixture of iodide or bromide 
of potassium, holding the silver salt in solution, may be em- 

The iodide of silver best adapted for this operation is said to 
be that which is obtained by treating, "\vith the aid of heat, a 
plate of this metal by the iodide precipitated from alcohol by 
water, aftei'wards dissolving the iodide formed and adhering to 
the plate in the hyposulphite. 

Dr. Berres, of Vienna, assisted by Mr. F. Kratochwila, has 
succeeded by another process, beai-ing some analogy to that of 
M. Fizeau, in fixing the daguerreotype designs. He takes the 
photograph produced in the usual manner by the process of 
Daguerre, holds it for a few minutes over a moderately warmed 
nitric acid vapom-, and then lays it in nitric acid of 13" or 14" 
Reaumur (61^" or 63^^ Falu-enheit), in which a considerable 
quantity of copper or silver, or both together, has been j^treviously 
dissolved. Shortly after having been placed therein, a precipi- 
tate of metal is formed, and can be changed to any degree of 
intensity. The photogTaphic picture coated with metal is now 
removed, washed in. water, cleaned, and dried ; it is then polished 
with chalk or magnesia, and a dry soft cloth or leather, after 
which the coating will become clean, clear, and transpai-ent, so 
that the pictiu-e, with all its details, can again be seen. 

This proceeding is of a most imcertain character — since, with 
every precaution, the acid solution frequently " bites" into the 
plate, producing an etching. 


Section VI. — Simplification of the Daguerreotype. 

The following experiments for tlie simplification of the daguer- 
reotype processes, were made by me many years since ; I have 
therefore retained such portions of the original paper as do 
not appear to be entirely uninstructive. 

Procure a well-plenished copper plate of the required size, 
and polish it, first with pumice-stone and water, than with snake- 
stone, and bring it up to a mirror surface with either rotten- 
stone or jewellers' rouge. Plates can be piu-chased in a high 
state of preparation from the engravers. Having prepared the 
copjDer plate well, rub it mth salt and water, and then with 
some silvering powder. No kiud answers better than that used by 
clock-makers to silver dial-plates. It is composed of one part 
of well-washed chloride of silver, five parts of cream of tartar, 
and four parts of table salt. This powder must be kept in a 
dai'k vessel, and in a diy 'place. For a plate six inches by five 
as much of this comjrtosition as can be taken up on a shilling is 
sufiicient. It is to be laid in the centre of the copper, and the 
fingers being wetted, to be quickly rubbed over every part of 
the plate, adding occasionally a little damp salt. The copper 
being covered with the silvering, it is to be speedily well washed 
in water, in which a little soda is dissolved, and as soon as the 
surface is of a fine silvery whiteness it is to be di-ied with a very 
clean warm cloth. In this state the plates may be kept for use. 
The fii'st process is to expose the jjlate to the heat of a spirit 
flame, until the silvered sm-face becomes of a well-defined golden- 
yellow colour : then when the lAate is cold, take a piece of 
cotton, dipped in veiy dilute nitric acid, and rub lightly over 
it until the white hue is restored, and diy it with very soft clean 
cloths. The plate is then immersed in a weak solution of the 
iodide of potassiiun, in which a small portion of iodine is dissolved. 
The silver is thus converted, over its sm-face, into an iodide of 
silver ; and in this state it is exposed to the solar rays, which 
blacken it. When diy it is to be again polished, either with 
dilute acid or a solution of carbonate of soda, and afterwards with 
diy cotton, and the smallest possible portion of prepared chalk ; 
by this means a sm-face of the highest polish is produced. The 
rationale of this process is, in the first 23lace, the heat applied 
di'ives ofi" any adhering acid, and efiects more perfect union 
between the copper and silver, so as to enable it to bear the 
subsequent processes. The fii'st yellow sui-face appears to be an 
oxide of silver, with, possibly, a minute qviantity of copper in 
combination, which being removed leaves a surface chemically 
pure. Copper plates may also be yqyj beautifully silvered by 


galvanic agency, by which we are enabled to increase the thick- 
ness of the silver to any extent, and the necessity for the heating 
process is removed, the silver being absolutely pure. The best 
and simplest mode is to divide an earthenware vessel with a 
diaphragm of membrane or paper : one side should be filled with 
a very dilute solution of sulphuric acid, and the other with either 
a solution of ferroprussiate of potash, or chloride of sodium, 
saturated with chloride of silver. The copper plate, varnished 
on one side, is united, by means of a copper wire, with a plate of 
zinc. The zinc plate being immersed in the acid, and the copper 
in the salt, a weak electric current is generated, which precipi- 
tates the silver in a very uniform manner over the entire sm'face. 

At a very early stage of my inquiries I foimd that the influence 
of all the rays, exceptiug the yellow, was to loosen the adhesion 
of the iodized surface, with the imder layer of unaffected sUver. 
When this changed film was removed by rubbing, the silver be- 
neath always exhibited the most perfect lustre, and I have hence 
invai'iably adopted this mode of polishing my dagiierreotype 
plates. The requii^ed surface is tlius produced with one-third the 
labour, and a very great savdng of time ; besides which, the silver 
is in a much more susceptible state for receiving the vapour of 
the iodine. The plate being thus prepared, we proceed in the 
manner before directed. 

It is somewhat singular, that on the first notice of Daguerre's 
pictm-es, long before the publication of his process, when I 
learnt that they were on " hard polished tablets," I entertained 
the idea that plates of copper thus silvered were oxidized, and 
then acted on by iodine. I applied the iodine both in solution 
and vapoiu- ; but, of coui-se, as the mercury was not used, I failed 
to efiect any perfect pictures. Tt is, however, worthy of i-emark, 
that on one occasion, having placed a piece of silvered copper in 
a trough containing a weak solution of iodine, with some leaves 
of hemlock superimposed, these being kept close by means of a 
piece of glass over all the exposed portions, the silver was 
completely removed, and the copper abraded to a considerable 
extent, while beneath the leaves the silver was scarcely affected. 
I thus procured a very beautiful etching, the figm-es being in 
high relief This was frequently repeated with success ; but 
other inqrdi'ies having di-a\\Ti off my attention, the process has 
been long neglected, although I am convinced it is capable of 
being turned to much useful account. 

In November, 1839, I pursued a series of experiments with 
bromine, but no veiy definite advantage was obtained. Some 
cui"ious effects which I noticed at that time are worthy of notice. 
I copy the remarks made in my memox'andum-book at the time. 


4. Exposed a plate to the vapour of bromine : it assumed a 
leaden-gray colovir, which, blackened by light veiy readily. Ex- 
posed this to mercury without much impro-sdng the effect or 
altering the lights. Upon immersing this plate in a solution of 
the mimate of soda, the parts unacted on by Kght became a jet 
black, whilst the paints on which light had acted were dissolved 
off, lea\'ing a clean coating of silver. The effect was most 
decisive — a black picture on a white ground. 

8. Allowed three plates to assume — the first a straw-yellow, 
the second a steel-blue, and the third a dull blue, and examined 
their sensitiveness ; the plate which had arrived at the dull blue 
colour appeared to be the most sensitive. 

These experiments, which were then pursued with a view to 
produce more permanent pictm-es — to fix the mercuiy, or to 
engrave the plate — were, however, abandoned, and have not yet 
been resumed, although it is desii-able that some one should 
tm-n his attention to this point. On one occasion, after ha\dng 
prepared a picture according to the process prescribed by 
Daguerre, T placed it, without removing the iodine, in a vessel of 
chlorine ; the pictvire was obliterated, and very speedily blackened. 
On expo.sing tliis black plate to light, it almost in.stantaneously 
whitened. This is mentioned to show the extent of ciu'ious 
subjects which jDhotography opens out for examination. 

The apparatus for the daguerreotype sho-wTi in the vignette 
may be enumerated with advantage. 

a. Is the camera obscura, T\^th the screen upon which the 
image is seen, and by which the focus is adjusted, partly raised ; 
and when this is accui-ately determined a screw is shown by 
which it is secured. 

b. Silver plate and edges for the same. 

c c. Are bromide and iodine boxes of walnut, enclosing each 
a stout porcelain pan : each pan is furnished with an air-tight 
glass cover. On the upper edge of each box is a groove for 
holding the plate. On withdrawing the glass cover of the iodine 
pan, the plate is exposed to its action, and the coloiu' produced 
is observed by holding a sheet of white paper in such a position 
that its reflection may be seen on the plate, which enables the 
operator to judge of the progi'ess of the operation. When the 
plate has obtained the requii"ed colour, the glass cover is pushed 
in, so as to cover the iodine pan, and the cover over the bi'omine 
pan is withdi-awn. The plate is now removed from the iodine 
box and placed over the bromine box, and the colour observed as 
before. When the plate has received the proper amount of 
bromine, which is perceptible by the colour, the cover of the 
bromine pan is pushed in, and the plate is again jjlaced over the 



iodine pan for a few seconds, until the ultimate colour required 
is produced, and it is then ready for removal to the camera. 

d. Improved mercuiy box, of walnut, with sliding legs, ii-on 
cistern, glass windows for ins]:)ecting the development of the 

picture, mounted with thermometer for ascertaining the tempera- 
ture of the mercuiy. 

e e. Are plate holdei-s, with clamp for securing the same. 

f. Is a box for holding the daguerreotype plates. 

(J. A levelling stand, used in the fixing process, see page 245. 

h. A flat peculiar dish for washing, see fig. 1, page 13. 

i. Is a hand-biiff. 

The pictures being completed, they are mounted in morocco 
or ornamented cases, such as are shown below. 



"With the advance of this beautiful art, there appears to be a 
progressively increasing desire to produce more artistic results ; 
and improvements are constantly being introduced. 

Collodion, as the film upon which to spread the photographic 
agents, beyond all other preparations, offers, in its exceeding 
sensibility, beavity of details in the finished pictures, and ease of 
operating, so many decided advantages, that a separate chapter 
has been devoted to its consideration. 

' Collodion is a peculiar preparation, formed by dissolving gun- 
cotton in ether containing a little alcohol. It is a very mucila- 
ginous solution of a volatile character, the ether evaporating and 
leaving a film of the utmost transparency behind. It is not all 
kinds of gun-cotton which dissolve equally well in ether.v Ac- 
cording to my experience the most easily soluble is prepared by 
soaking good cotton in a saturated solution of nitrate of potash 
for some time ; it is then, in a moist state, plimged into sulphiu'ic 
acid with which but a small quantity of nitric acid has been 
mixed : after remaining in the acid for about a minute, it is well 
washed with water until no trace of an acid taste is discovered, 
and then dried at a temperatui'e but very slightly elevated above 
that of the apartment. ^^ 

Mr. Archer, to whom, with Mr. Fry, we are mainly indebted 
for the introduction of this preparation as a photographic agent, 
gives the following as his processes for j^reparing gun-cotton : — 

" There jire two receipts for making g-un-cotton, from either of 
which a good dissolving cotton may be obtained. Several others 
have been described, but I should only be confusing the subject 
to attempt to give the whole ; and it would be foreign to the 
limited piu'pose of this work to do so. The results, however, 
vary so much with the strength and proportion of the acids 
used, as to render it extremely difficult to name any one in 
particular which would entirely succeed under all circumstances. 
In all cases it is more easy to prepare a cotton which will 
explode readily, and yet not he at all soluble, than one which will 
entii'ely dissolve in rectified sulphuric ether. 


Take of cliy niti-ate of potash in powder, 40 parts 

Sulphm'ic acid 60 ,, 

Cotton 2 „ 

" The nitre, sulphuric acid, and cotton, are weighed in the 
above proportions, and placed near at hand within reach of the 
operator, to prevent delay in mixing when the operator has 
commenced. Then pom* the propoi-tion of sulphiiric acid into 
the powdered nitre, stii'iing them well together for a few 
seconds with a strong glass rod. Immediately the two ai-e 
mixed add the cotton, having previously pulled out the fibres, 
and mix them well together with two glass rods, in order that 
the whole of the cotton may come in contact with the nitric 
acid vapour, which is being i-apidly generated from the mixture. 
This action mtist be continued for about two minutes ; then 
quickly remove the cotton mth the adhering nitre and sulphuric 
acid from the basin, with the glass rods, and plunge it into a 
large quantity of water ; it is to be well washed in repeated 
changes of water until all the acid and nitre are washed away. 
The cotton is then collected togethei-, and first pressed between 
the hands to ch'ain ofi" the water, and then still fui-ther dried by 
pressui'e in a cloth ; the fibres of cotton can now be carefully 
separated, and himg up wdth pins to the edge of a shelf, or any 
other convenient place, to diy. There is no necessity to use 
artificial heat, as the small quantity requisite for a few oiinces 
of solution can easily be di'ied without it. 

'' The next receipt is by certain proportions of nitric and 
sulphuric acids : — 

Take 1 oz. by measure of nitric acid, specific gi-avity 1-450 
1 oz. „ sulphuric ditto ordinary 

80 gi's. by weight of cotton. 

" The fibres of cotton must be well separated, as in the pre- 
ceding mode. The two acids are first mixed, and the requisite 
proportion of cotton added as quickly as possible, and weU 
stii-red with two glass rods for not more than fifteen seconds : 
the gun-cotton is removed from the acids, and plunged into 
water to vmdergo the same washings, &c., as in the former 

" It will be seen that the cotton is not exposed to the action 
of the mixed acids, in this last mode, longer than is necessary to 
satvirate the cotton ; should the action be continued further, the 
solubiUty of the cotton is entirely lost. 

" Water must not be spared in washing the cotton, for not a 
trace of acid should be left ; the collodion would be injiu'ed by 
any remaining." 


The substance lignine — wliicli is tlie tiiie wood of every variety 
of plantj and has the composition C 38, H 24, O 20 — is capable 
of being converted into a material having an analogous constitu- 
tion to true gun-cotton. With strong nitric acid lignine com- 
bines directly, and forms a substance called xyloidine. This may 
be prepared by immersing a piece of paper in strong nitric acid, 
and then washing it well in piu'e water ; it thus assumes the 
feel and toughness of parchment, and is so combustible as to 
serve for tinder. The composition of xyloidine is expressed by 
C 12, K 2, H 8, O 18. Starch dissolves by digestion in strong 
nitric acid, and on adding water xyloidine is precipitated. There 
are several other materials of which it may be prepared, and 
nearly all these substances are soluble in ether, forming collodion. 

Gun cotton is a compound of lignine with nitric acid — 100 
parts of cottou producing 170 parts of gun-cotton. 

To Prepare the Collodion. — Thirty grains of g-im-cotton pre- 
pared as described should be taken and placed in 18 fluid ounces 
of rectified sulphiu-ic ether, and then 2 ounces of alcohol should 
be added ; making thus an imperial pint of the solution. The 
cotton, if properly made, will dissolve almost entirely ; any small 
fibres which may be floating about should be allowed to deposit, 
and the clear sokition poured oflf previously to the process of 
iodizing it. Mr. Delamotte adds a few drops of ammonia to the 
collodion, which may possibly prevent an acid reaction, which 
sometimes takes place. 

To Iodize the Collodion. — Mr. Ai-cher's method is as follows ; 
and I believe no better course can be piu'sued. 

Prepare a saturated solution of iodide of potassium in alcohol, 
say 1 oz., and add to it as much iodide of silver as it will take 
up. Or to 1 oz. of alcohol add an excess both of iodide of po- 
tassium and iodide of silver ; after a day or two, and with repeated 
shaking at intervals to facilitate the operation, a satui-ated solu- 
tion of the two salts will be obtained, and if this is filtered ofi" 
into another bottle, it will always be found ready for use. The 
first bottle can be kept as a stock bottle, to obtain a still further 
supply by replenishing it with alcohol, and adding now and then 
small additional quantities of the two salts. The iodide of sil- 
ver can be readily obtained by precipitation. For instance, take 
1 oz. of solution of nitrate of silver used in the process, 30 grs. 
of nitrate of silver to 1 oz. of water, and add to it sufiicieut of a 
solution of iodide of potassium in water as wiU throw down the 
whole of the nitrate of silver as an iodide. When this precipi- 
tated iodide of silver has settled, which it very readily does, the 
liquid above must be poured off", and fresh water added, repeat- 
ing this washing several times. The iodide of silver after this 


is dried, and then put into a bottle with a small quantity of 
alcohol, just sufficient to keep it moistened. The quantity of 
the solution of iodide of silver which can be added to 1 oz. of 
collodion, must depend upon the quantity of alcohol in the col- 
lodion. Iodized collodion is liable to decomposition, and iodine 
is liberated. This is prevented by putting a little piece of pure 
metallic silver in the collodion, which preserves it colovu'less and 
of a constant strength. The collodion process now resolves itself 

1st. Cleaning the Glass Plate, — One of the most successful 
general manipulators in the oixlinary forms of the collodion pro- 
cess is Mr. Home, to whom I am indebted for much important 
information on this process. A variety of substances, such as 
tripoli, nitric acid, spiiits of wine, (fee, have been recommended 
for cleaning the glass : but all these Mr. Home thinks are quite 
superfluous; the only articles actually necessaiy being a clean 
cloth or two, and a wash leather that has been well and tho- 
roughly rinsed tlii'ough several changes of clean water, to deprive 
it as much as pos.sible of the di'essing which a new one contains, 
and a httle liquid ammonia, not strong, but the ordinary liquor 
ammonue of the shops. If this is not at hand, a little caustic 
potash or soda will answer as well, the pm-poi-t of it being to 
remove any greasy matter attached to the sui-face, as glass is 
frequently mai-ked \nih. soap; and although it might appear at 
first sight that clean water must thoroughly remove this article, 
the operator will be certain of spoiling many of his pictui-es if he 
depend upon water alone. 

The plan ]Mr. Home recommends is as follows : — Poui- upon 
the plate a few drops of ammonia, rub it well over both surfaces, 
and thoroughly rinse through two waters, allowing the water to 
flow over the plate either by poiu-iug from a vessel or holding 
under a tap; now, with a clean cloth wipe perfectly diy, and 
finally well mb Avith a leather. Simple as this may appear, 
there is much more in it than will be at first imagined, for un- 
less the glass is free fr-om stains it is quite impossible to l)e suc- 
cessful. The plate may be washed perfectly clean, but the sur- 
face not thoroughly di-ied. Then, again, some hands are very 
warm, and if the plate is allowed to rest too much upon any one 
part, or held too long in the fingers at any one particular spot, 
that will become warmer than the siuTounding part, from the 
glass being a bad conductor of heat. The cloth and leather 
should therefore be sufficiently large, that the plate ma\' be as 
it were insulated as much as possible from the hands, that no 
unnecessary lieat shall be applied. At the same time the em- 
ployment of a waim cloth is very useful, for the heat is then 


equally diffused over the plate, and, is very essential, tlie 
surface perfectly and quickly di-ied. 

Coating the Plate. — It lias ali-eady been pointed out liow 
necessaiy it is to handle the plate as little as possible in cleaning ; 
we therefore suppose the operator to have the plate in a clean dry 
leather, from which it is taken to receive the collodio-iodide of 
silver. The plate must be held hj the left hand perfectly hori- 
zontal, and then with the right a sufficient quantity of iodized 
collodio should be poiu*ed into the centre, so as to diffuse itself 
equally over the su.rface. This should be done coolly and steadily, 
allowing it to flow to each corner in succession, taking cai-e that 
the edges are all well covered. Then gently tilt the plate, that 
the superfluous fluid may return to the bottle fi'om the opposite 
corner to that by which the plate is held. At this moment the 
plate should be brought into a vertical position, when the 
diagonal lines caused by the fluid runniug to the corner vnll fall 
one into the other and give a clear flat surface. To do this neatly 
and effectually, some little practice is necessaiy, as in most tilings, 
but the operator shoidd by no means huny the operation, but do 
it systematically and quietly, at the same time not being longer 
over it than is actually necessary, for collodion being an ethereal 
compound evaporates very rapidly. Many operators waste their 
collodion by imagining it is necessary to perform this operation 
in great haste ; but such is not the case, for an even coating can 
seldom be obtained if the fluid is poured on and off again too 
i-apidly ; it is better to do it steadily, and submit to a small loss 
from evaporation. If the collodion becomes too thick, thin it 
with the addition of a little fresh and good ether. 

Exciting the Plate. — Previous to the last operation it is neces- 
sary to have the liath ready, which is made as follows : — 

Nitrate of silver 30 grains. 

Distilled water 1 ounce. 

Dissolve and filter. 

The quantity of this fluid necessary to be made must depend 
upon the form of trough to be used, whether horizontal or verti- 
cal, and also upon the size of j^late. The kind used by Mr. Home 
is the vertical, though many stdl jirefer the former, and attach 
a piece of Indian rubber to the back of the plate as a handle 
whilst applying the collodion, and to keep the fingers from the 
solution whilst dipping in the bath. "With the vertical troughs 
a glass dipper is provided, upon wluch the plate rests, preventing 
the necessity of any handle or the fingers going into the hquid. 
If, however, the glass used is a Little larger than is required, this 


is not necessary. Having then obtained one or other of these 
two, and filtered the liquid, previously fi-ee fi'oni any particles 
of dust, (fee, the plate is to be immersed steadily and icithout 
hesitation, for if a paivse shoiild be made at any paii, a line is 
sure to be formed, which will print in a subsequent part of the 

The plate being immei'sed in the solution, must be kept there 
a sufficient time for the liquid to act freely upon the surface, 
particularly if a negative picture is to be obtained. As a. general 
rule, it vAll take about two minutes, hut this will vary imth the 
temperature of the air at the time of operating, and the condition 
of the collodion. In cold weather, or indeed anything below SO'* 
Fakrenheit, the bach should be placed in a warm sittiation, or 
a proper decomposition is not obtained under a veiy long time. 
Above 60' the plate will be certain to have obtained its maxi- 
mum of sensibility by two mintites' immersion, but below this 
temperature it is better to give it a little extra time. 

To facilitate the action, let the temperature be what it may, 
the plate mtist be lifted out of the liquid two or three times, 
which also assists in getting rid of the ether from the surface, 
for without this is thoroughly done a uniform coating cannot 
be obtained; but on no account should it be removed until the 
plate lias been immersed about half a minute, as marks are apt to 
be produced if removed sooner. 

Having obtained the desired coating, the plate is then ex- 
tremely sensitive, and, therefore, we presume the operator has 
taken eveiy precaution to exclude ordinary day-light. 

The room must be closed against any portion of day -light, and 
candle alone employed, placed at a distance from the operator to 
give the requisite light. Yellow glass, which has been recom- 
mended for glazing the operating room, does not furnish suffi- 
cient protection from the chemically active rays. 

The plate thus rendered sensitive must then be lifted from 
the solution and held over the trough, that as much liquid as 
possible may drain off previous to its being placed in the frame 
of the camera, and the more efiectually this is done the better ; 
at the same time it must not be allowed to dry. 

The question is often asked, how soon after coating the plate 
with iodized collodion should it be immersed in the nitrate 
bath? Now, this is a difficult question to answer. We have 
said the time of immersion is dependent upon the tempera- 
ture and quality of the collodion ; so likeA\"ise must we be 
governed as to time before immersion. To make collodio-iodide 
or xylo-iodide, for, chemically speaking, there is no difierence 


in the two, it is necessary that the ether should contain a 
certain quantity of alcohol, or the cliiFerent ai"ticles are not 
soluble : therefore, if we take a fresh bottle, and coat the plate 
from this, it contains its full dose of ether, and wdth the 
thermometer ranging between 60° and 70° the evaporation will 
be very rapid, and consequently a tough film soon formed. If, 
on the other hand, we are using a solution which has been in use 
some time, and many plates, perhaps, coated, the proportion of 
alcohol is much greater, and not being of so volatile a natiu'e, it 
will necessarily take a longer time to acquii-e the requisite fii'm- 
ness for immersion. If, for instance, after coating a plate, we 
find on immersion it does not colour freely, we have then reason 
to suppose the plate has not been immersed sufliciently quick ; 
but if, on the other hand, we find the film very tender, and upon 
(hying it cracks, then we have reason to know that plates pre- 
pai-ed fr-om that bottle must not be immersed qmte so soon. 
The larger the proportion oj' alcohol tlie more sensitive ivill be the 
2)lates, and the quicker and inore even ivill he the action of the 
bath; but a longer period may be allowed for the sensitive film 
to hai'den before immersion. 

The next question also often asked is, how long must be the 
exposiu'e in camera? a question more difficult to answer than 
the last, without knowing something of the character of the lens 
and the intensity of sunshine. Practice alone can determine, 
combined with close obsei-vation of those parts which shotJd be 
the shadows of a pictiu-e. If, for instance, in developing we find 
those parts less exposed to the light than others developing im- 
mediately the solution is applied, then we have reason to suppose 
the exposui-e has been too long ; but if, on the contraiy, they 
develope veiy slowly, we have proof the time allowed has not 
been sufficient to produce the necessaiy action. In a good pic- 
tui'e we should see first the whites of a di'ess appear, then the 
forehead, after which we shall find, if the light has been pretty 
equally diffused, the whole of the face, and then the dress. 

The following remarks, by the Count de MontLzon, are of 
value — 

To Iodize Collodion. — I have tried many methods of iodizing 
collodion. Those which have given the most successful results 
are the following : — 

1st. In 1 oz. of collodion put a little iodide of sUver and about 
3 or 4 graius of iodide of potassium, and then shake it well up. 
The collodion becomes veiy tiu-bid, but on being left for some 
hoiu's it gradually clears up, begiuuing at the bottom. When it 
is quite clear, pour off the liquid into another bottle. 


2d. To 1 oz. of collodion add 2 grains of iodide of ammonium. 
This ■will give veiy beautiful gradation in the half-tones, but not 
so vigorous a picture as the first. 

3d. In 8 di-achms of pure alcohol dissolve perfectly 8 grains of 
iodide of ammonium or iodide of potassium, and i grain of iodide 
of silver; then add 24 drachms of collodion. The iodide of silver 
ought to be fi'eshly made, or the residting negative vrill be of 
inferior quality. The iodide of ammonium too ought to be 
newly made. This collodion is one of the most sensitive, but 
the half-tones produced by it are inferior. 

4th. In 8 drachms of alcohol dissolve 8 grains of iodide of 
potassium, 4 of iodide of ammoniiun, and ^ grain of iodide of 
silver; then add 24 drachms of collodion. This forms a very 
sensitive medium. 

5th. In 2^ oz. of coUodion, 5 drachms of alcohol and 5 minims 
of liquid ammonia, dissolve 14 gi-ains of iodide of ammonium. 
This forms a very good collodion, veiy sensitive and coloiu'less. 

6th. In 2 di-achms of alcohol dissolve 6 grains of iodide of 
potassium, and add 6 drachms of coUodion. 

We now come to the 

Method of Operating. — I employ nothing but water to clean 
the glass plate with, using plenty of it, and iiibbing the glass 
with the hand till the water flows freely over the surface. It 
must be well chied and nibbed clean with a linen cloth wliich 
has been well washed without the use of soap. When the col- 
lodion comes away from the glass, it is almost always in conse- 
quence of the existence of grease or dirt, or of a little moisture 
upon the siu-face. 

Pour the coUodion upon the glass in the usual way, and 
almost immediately immerse it in the bath of nitrate of sUver, 
30 grains to the ounce of water, lifting it in and out of the solu- 
tion to allow the ether to escape. When it assumes a bluish 
opal hue, it is ready for use. By adding a Uttle alcohol to the 
solution, one part of alcohol to ten parts of water, and one part 
of nitrate of silver, the collodion is more speedily rendered sen- 
sitive, and the image produced is more vigorous. 

It seems of some importance to immerse the glass in the 
nitrate bath, and to place it in the slide in the same direction as 
that in which the coUocHon was poured off the glass plate. 

After the appearance of the opal hue, if the bath be an old 
one, the plate may be left in it for some time without injmy ; 
but if the bath be new, it must not be left longer than is neces- 
sary to excite, or the rdtrate would attack the iodide of silver. 

To obviate this, it is weU in making a new bath to add 1 
grain of iodide of sUver to each ounce of the nitnite solution. 


It is unnecessary to filter the bath, as it is often altered in its 
nature by passing thi-ough paper containing injimous chemical 
constituents. A little blotting-paper di'awn over the surface 
will remove any particles of dust that may be floating upon it. 

If the bath contain alcohol, it should, when not in use, be 
kept in a stoppered bottle. 

The Development of Image. — To effect this the plate must 
be taken again into the room, and with care removed from the 
slide to the levelling stand. 

It wiU be well also to caution the operator respecting the re-' 
moval of the plate. Glass, as before observed, is a bad conductor 
of heat ; therefore, if in taking it out we allow it to rest on the 
fingers at any one spot too long, that portion will be warmed 
through to the face, and as this is not done until the developing 
solution is ready to go over, the action will be more energetic 
at those parts than at others, and consequently destroy the 
evenness of the picture. We should, therefore, handle the jjlate 
with cai'e, as if it already possessed too much heat to be com- 
fortable to the fingers, and that we must therefore get it on the 
stand as soon as j)ossible. 

Having then got it there, we must next cover the face with 
the developing solution. 

This should be made as follows : — 

Pyrogallic acid 5 grains. 

Distilled water 10 oz. 

Glacial acetic acid . . . . 40 minims. 
Dissolve and filter. 

Ml'. Delamotte employs 

Pyrogallic acid 9 grains. 

Glacial acetic acid .... 2 drachms. 
Distilled water 3 ounces. 

Now, in developing a plate, the quantity of liquid taken mvist 
be in proportion to its size. A plate measuring 5 inches by 4 
will require half an ounce ; less may be used, but it is at the risk 
of stains ; therefore we would recommend that half an ounce of 
the above be measured out into a per/ectli/ clean measure, and 
to tliis from 8 to 12 drops of a 50 grain solution of nitrate of 
silver added. 

Pour this quickly over the surface, taking care not to hold the 
measure too high, and not to pom- all at one spot, but having 
taken the measure properly in the fingers, begin at one end, and 
carry the hand forward ; immediately blow ujdou the face of the 
plate, which has the efi'ect not only of difiusing it over the sur- 


face, but causes the solution to combine more equally witli the 
clamp surface of the plate : it also has the effect of keeping any 
deposit that may form in motion, which, if allowed to settle, 
causes the picture to come out mottled. A piece of white paper 
may now be held under the plate, to observe the development of 
the pictiu'e; if the light of the room is adapted for viewing it in 
this manner, well; if not, a light must be held below, but in either 
case arrangements should be made to view the plate easily whilst 
under this operation, a successfid result depending so much upon 
obtaining sufficient development ■without caiTying it too far. 

As soon as the necessary development has been obtained, the 
liquor must be poured off, and the siu'face washed with a little 
water, which is easily done by holding the plate over a dish and 
pouring water on it, taking cai-e, both in this and a subseqixent 
pai't of the process, to hold the plate horizontally, and not ver- 
tically, so as to prevent the coatmg being torn by the force and 
weight of the water. , 

Protosulphate of iron, which I first introduced as a photogra- 
phic agent in 1840, may be employed instead of the pyi-ogallic 
acid with much advantage. The beautifid collodion portraits 
obtained by Mr. Tunny of Edinbui'gh, are all developed by the 
ii'on salt. The following are the best proportions : — 

Protosulphate of iron .... 1 oz. 

Acetic acid 12 minims. 

Distilled water 1 pint. 

This is to be used in the same manner as the former solutions. 

Fixings of Image. — This is simply the removal of iodine 
from the siu'face of the plate, and is effected by pouring over it, 
after the water, a solution of hyposulphite of soda, made of the 
strength of 4 oz. to a pint of water. At this point daylight may 
be admitted into the room; and, indeed, we cannot judge well 
of its removal without it. We then see, by tilting the plate to 
and fro, the iodide gradually dissolve away, and the different 
parts left more or less transparent, according to the action of 
light upon them. 

It then only remains to thorovighly wash away every trace of 
the hyposulphite of soda, for, should any of the salt be left, 
it gradually destroys the picture. The plate should, therefore, 
either be immersed with great care in a vessel of clean water, 
or, what is better, water poiu'ed gently and carefully over the 

After this it must be placed upright to dry, or held before afire. 

We have now carried the operator carefully thi-ough every 
stage of the process, from the cleaning of plate to the fixing of 


image ; but our remarks have reference to collodio-iodide alone ; 
that is gun-cotton dissolved in ether, charged wdth an iodide of 
sUver. "We cannot, however, consider our task finished ^\^thout 
mentioning the addition of gutta-percha to the collodion. This 
valuable discovery was made by Mr. P. W. Fry, to which gentle- 
man belongs some of the most iinporcant steps made in the 

The sensibility of the plates appears to be more materially in- 
creased by the addition of the gutta-percha ; indeed, pictures by 
superposition may be obtained with absolute instantaneity, and 
in the camera oljscvira in less than a second of time. 

The plan of proceeding to obtain this extreme sensibility, as 
recommended by Mr. Fry, is to obtain a thick and strongly 
charged collodio-iodide, and to two parts of this add one of a 
saturated ethereal solution of gutta-percha, allowing it to stand 
a day or two to clear itself, previous to being used. 

The plate is ihen coated iu the usual manner. As the ether 
evaporates a peculiar white film comes over, at which time it is 
ready for immei*sion in the bath. This must be conducted as 
previously described, and, from its extreme sensibility, with, if 
possible, greater precaution than before. 

For the development of negative pictures, Mr. Fry recom- 
mends the pyi'Ogallic solution, rather stronger than that pre- 
viously given, about one gi-aiu to the ounce, "s\dth the addition 
of an extra portion of acetic acid, and the plate re-dipped in the 
nitrate hath, in preference to adding silver solution to the pp'o- 
gallic acid. 

In fixing the image after development, it is necessary to keep 
the hyposidphite on longer than "ndth the ordinary collodion, as 
the iodide is held -svdth greater tenacity. In other respects the 
method of jwoceeding is precisely the same. 

Mr. Thomas has modified the collodion process as follows : — 

1 st. To prepare the glass. — Roughen the s\u*face of the edge about 
one-sixteenth of an inch all roimd A^ith coarse emery paper ; tliis 
prevents contraction of the film, and enables you to pump upon 
it, if necessary, Avithoiit any fear of coming off. 

2d. To clean the glass if nev/. — Make a mixtiu'e of spirits of 
wine and liquor ammonia equal parts, render it as thick as cream 
with tripoli ; with a piece of cotton wool, kept for this purpose, 
rub a small quantity over that side scratched as described, wash 
well under a tap of water, and wipe diy with a piece of old 
linen washed A\dthout soap, and kept scrupulously clean for this 

N.B. To clean a glass after having tised it, when not var- 
nished, wash off the collodion film with water, and chy as above. 


Always Avipe tlie glass jiist before use, and breathe upon it ; if 
clean, the moisture evaporates evenly. 

3d. Pour into the centre as much collodion as the glass will 
hold, and poiu' off at that corner diagonal to the one by which 
the glass is held : prevent the formation of lines, by altering 
quickly the position of the glass before the film dries ; with 
observation and practice dexterity is easily acquii-ed. 

l:th. As soon as the collodion ceases to nm, plimge the pre- 
pai'ed glass, without stopping, into the following bath : — 

Into a 20-oz. stoppered bottle put 

Nitrate of silver 1 ounce. 

DistHled water IG ounces. 


Iodide of potassium .... 5 grains. 

Distilled water 1 di-achm. 


On mixing these two solutions a precipitate of iodide of sUver 
is formed. Place the bottle containing this mixture in a sauce- 
pan of hot water, keep it on the hob for about twelve hoiu"s. 
shake it occasionally, now and then remo^-ing the stopper. The 
bath is now perfectly satm-ated ■n-ith iodide of silver ; when 
cold, filter through white filtering paper, and add. 

Alcohol 2 drachms. 

Sulphui-ic aether ... 1 di-achm. 

A convenient way of satiu'ating the nitrate of silver bath 
Avith iodide of silver, is to di&solve the 1 oz. of nitrate of sil- 
ver in 2 oz. of the water, add the solution of iodide of potas- 
sium to this strong solution ; the precipitate thus foiTiied is by 
shaking entii-ely dissolved; now add the remaining 14 oz. of 
water, when the iodide of silver is again thi'own down, but in 
such a finely divided state as to render the complete saturation 
of the bath more perfect, obviating the necessity of frequent 
shaking. After half an hour, add the alcohol and ether, and filter. 

oth. Allow the pi-ej^ared glass to remain in this bath eight or 
ten minutes : just before taking it out move it up and down 
three or four times; drain it, but not too closely; when in the 
frame place upon the back a piece of common blotting-paper to 
absorb moisture ; the sooner it is placed in the camei-a the better. 

6th. The time of exposure can only be ascertained by pi'actice, 
no rules can be laid down, and I am unacquainted with any 
royal road but that of experience, leading to constant success in 
this most important section of photogi"aphy. 

7th. The plate being taken from the camera and placed upon 


a levelled stand, develope immediately the latent image with the 
following solution : — 

Pyrogallic acid 3 grains. 

Distilled water 1 ounce. 

Acetic acid (glacial) ... 1 drachm. 

Take one part of this solution and two parts of distilled water 
for use. The pyrogallic solution made with proper acetic acid 
and of the above strength, may be kept for a month or more in 
a cool place away 6'om the light. 

8th. When the image is sufficiently intense, wash freely with 
common filtered water; then pour on a saturated solution of 
hyposulphite of soda, which should immediately remove the 
iodide of silver, wash again well with water ; allow as miich as 
the plate will hold to soak in for at least half an hour, to re- 
move aU ti-aces of hyposidphite of soda ; lastly, stand up to dry, 
and if required, varnish with amber varnish. 

Having, by the foregoing means, obtained and fixed a negative 
photographic image on glass, and which is capable of producing 
positives upon paper by the ordinary photographic means, it is 
as well, previous to obtaining these, to render the tender film of 
collodion less liable to injury. 

This can be accomplished by means of a varnish, of which 
there are different kinds that may be used. 

By far the best kind of varnish which can be employed is one 
for which we are indebted to Dr. Diamond. This is made by 
powdering some amber and putting it into clxloroform ; by the 
application of a gentle heat under pressure, with care, a perfect 
solution takes place. This varnish flows readily over the plate, 
and dries in a few minutes, leaving a beautifully transparent 
hard glaze upon the picture. 

It was shown by Mr. Home in the early days of coUodion, 
that the negative images could be converted into positive ones 
by mixing with the pyrogallic solution a very small quantity of 
nitric acid ; but it has since been sho^vn by Mr. Fry, and others, 
that a better result may be obtained by the use of proto-sulphate 
and proto-nitrate of iron. 

The former salt is readily obtained, and in a very pure form. 
It should be used as follows : — 

Proto-sulphate of iron . . . . 10 grains.- 

DistiUed water 1 oz. 

Nitric acid ....... 2 drops. 

To develope the image pour the above over the plate, taking care 
not to caiTy the development too far. 



The proto-nitrate may be obtained by double decomposition, 
as recommended by Dr. Diamond : 600 gi-ains of proto-sulphate 
of iron are dissolved in one ounce of water, and tbe same quantity 
of nitrate of baryta in six ounces of water ; tliese being mixed 
together, proto-nitrate of iron and sulphate of baiyta are formed 
by double decomposition ; also by dissolving sulphuret of iron 
in dilute nitric acid, as recommended by jNIr. Ellis, who proceeds 
as follows : — 

To one ounce of nitric acid and seven of water, add a small 
quantity of sulphuret of iron broken into fragments. Place the 
vessel aside, that the sulphnretted hydi-ogen may escape, and the 
acid become saturated with ii'on. Pom- oif the liquid, and filter. 
Then boil ux a florence flask, to get rid of the sulphm-, and again 
filter, when a dark green liquid will be obtained, which is the 
proto-nitrate of iron. This should be kept in well-stopped 
bottles, and protected from the aii- as much as possible, to prevent 
its changing into a pernitrate, in which state it is quite useless 
as a photogi-aphic agent. 

To develope the picture mix one part of the above proto- 
nitrate with three of water, and apply it to the plate in the 
ordinary way, when a most beautiful clear image can be obtained. 

The negative image being developed, a mixtui'e of pyi-o-gallic 
and hypo-sulphite of soda, which has imdergone partial decom- 
position, is potired over the plate, and then it is gently warmed. 
Upon this the darkened parts are rendered brilliantly white by 
the formation of metallic silver. This picture being backed 
up with black velvet assumes the air of a fine daguerreotype, 
without any of the disadvantages arising from the reflection of 
light from the polished silver siu-face. For this beautiful residt 
photogi-aphy is indebted to Dr. Diamond, who is still pm-suing 
the subject with much zeal. We have also seen similar efiects 
produced by Mr. Fry and Mr. Berger, by the use of the proto- 
sulphate of iron solution and pyi-ogallic acid. The image is first 
developed by the iron and the solution poured ofi"; immediately 
another of pyrogallic acid is poured on, and the efiect is produced. 

The pictm-es are fixed with the hyposulphite in the usual 

A peculiar whitening process was introduced by Mr. Archer, 
which is as follows : — 

The pictiu'e being thoroughly washed in plenty of water, after 
fixing with hypo-sidphite of soda, is treated in the following 
manner : — 

Prepare a saturated solution of bi-chloride of mercury in mu- 
riatic acid. Add one part of this solution to six of water. Pour 
a small qiiantity of it over the pictiu'e at one corner, and allow 


it to inin evenly over tlie glass. It will be found immediately to 
deepen the tones of the pictm-e considerably, and the positive 
image will almost disappear ; presently, a peculiar whitening will 
come over it, and in a short time a beautifully delicate white 
picture will be brought out. 

The negative character of the drawing will be entirely de- 
stroyed, the white positive alone remaining. This picture, after 
being well washed and dried, can be varnished and preserved as 
a positive ; but nevertheless, even after this bleaching, it can be 
changed into a deep-toned negative, many shades darker than it 
was oi'iginally, by immersing it, after a thorough wasliing, in a 
weak solution of hyjjo-sulphite of soda, or a weak solution of 
ammonia. The white pictm^e will vanish, and a black negative 
will be the result. 

It is very singular that the pictiu"e can be alternately changed 
from a white positive to a black negative many times in succes- 
sion, and very often with improvement. 

Thus, by the above process, a most perfect white positive 
or a deep black negative is produced, quite distinct from each 

In the first part of this after-process, it will be observed that 
the effect of this bi-chloride of merciuy solution is to deepen the 
shades of the picture, and this peculiarity can be made available 
to strengthen a faint image, by taking the precaution of using 
the sokition weaker, in order that the first change may be com- 
pleted before the whitening effect comes on. 

The progress of the change can be stopped at this point by 
the simple appliciation of water. 

The author first pointed out the remarkable action of corrosive 
sublimate, in his paper, published by the Royal Society, on the 
Daguerreotyjie process on paper. 

M. Adolphe Mai-tin has published some remarks on the col- 
lodion in the Comptes Rendus of 5th July, 1852. 

The collodion he employs is made of — 

30 gi'ains of cotton. 
750 grains of nitrate of potash. 
1500 gi-ains of sulphuric acid. 

This is well washed and dissolved in 10 volmnes of ether and 1 
volume of alcohol : by this, 15 gr'ains of gun-cotton are dissolved 
in 1860 grains of ether, and 930 grains of alcohol : add then to 
this collodion, 15 gx'ains of nitrate of silver transformed into 
iodide, and dissolved in 20 grains of alcohol by means of an 
alkaline iodide. M. Adolphe Martin prefers iodide of ammonium. 
The plate is next plunged into a bath of 1 part distilled water, 


1 x^gth nitrate of silver, and l^^jth nitric acid. The image is 
developed by proto-snli^hate of iron, and he effects the change 
from negative to positive by a bath of double cyanide of silver 
and potash, consisting of about 2 quarts of water, in which are 
dissolved 375 grains of cyanide of potassium, and 60 grains of 
nitrate of silver. The pictures thus produced are remarkable 
for their intense whiteness. 

We must allow jMr. Archer to give his own description of the 
very ingeniously constracted camei'a, which he has devised for 
the collodion process. The practice of the collodion process in 
the open air is a matter of some difficulty ; some ingenious 
cameras have been devised for this piu'pose ; but thei-e are few 
better contrivances than that introduced by Mr. Archer, and 
modified by Messrs. Griffin & Co. 

Description of the Camera for the Collodion. — '• I will proceed 
to give a general description of the camera I have constnicted, 
premising that it admits of being made as a very light folding 
camera, if thought necessary. 

"It is a wooden box, 18 inches long, 12 inches wide, and 12 ' 
inches deep, and is capable of taking a picture 1 inches square. 
Externally it may be thus described : — In front it has a sliding 
door, with a circular opening in it, to admit the lens : this 
sliding door enables the operator to lower, or raise, the lens, 
and consequently the image fonned by it, on the ground glass, 
as the view may require. The two sides of the camera have 
openings cut in them, into which sleeves of India nibber cloth 
are fixed, to admit the hands of the operator, and are ftu-nished 
with India rubber bands at the lower ends, which press against 
the wi'ists, and prevent the admission of light. 

" The back of the camera has a hinged door fitted at its 
upper part -sv-ith an opening of just sufficient size for the eyes, 
and shaped so as to fit close to the face. A black cloth is tied 
round this end of the camera, to prevent any ray of light 
peneti-ating at this opening. In the top of the camei-a, neai' 
the front, is inserted a piece of yellow glass, to admit a small 
quantity of yellow light, and is closed with a hinged door, to 
regulate the quantity of Hght reqviired. 

" The interior of the box is fiii-nished with a sliding frame, 
to support the ground glass or the bath and the prepared plate ; 
and it has a stop, by means of which any focus from 3 inches to 
15 inches can easily be obtained. 

" The bottom of the camera is furnished with a gutta percha 
tray, about 1 inch deep, to hold the washings, &c., when the 
camera is in operation. 

" Also, the bottom of the camera at the back has an opening 


cut in it, extending nearly the whole width of the camera, and 
as far in as the edge of the gTitta percha tray. 

" This opening is intended to admit, when the camera is in 
use, a light wooden case containing the glass bath, focusing 
frame, stock of glass, and paper required in the process. 

" There are various other little contrivances which I have 
not specified ; such as a drawer for the pictures, a shelf for 
bottles, &G. 

This form of camera will admit of the following manipu- 
lation : — Having placed it upon a stand pointing to the object 
to be taken, the hinged door at the back is opened, and the bath 
is three parts filled with the solution of nitrate of silver ; a 
plate of glass is then taken from the cell, and cleaned if • 

"The collodion is poured on in the manner previously de- 
scribed; when the film has set a little it is immersed in the 
nitrate of silver bath, and the lid of the bath is closed down 
upon it. The next step is to obtain the focus with the ground 
glass : this can be done whilst the collodion is becoming iodized. 

"After adjusting the sliding frame to the proper focal distance, 
the camera must be closed, and the rest of the process conducted 
by passing the hands through the sleeves, and placing the eyes 
close to the aperture in the back of the camera, and drawing the 
black cloth over the front of the head. 

" By the aid of the yellow light admitted from the top, the 
operator can carry on the rest of the process. The plate is now 
ready for the action of light, and is taken from the bath ; or the 
bath itself, with the plate in it, is placed in the sliding frame 
The refracted image is at once thrown upon the sensitive plate. 
After the reqviisite exposure, the plate is taken from the bath, 
and the picture is developed with the solution previously 
described. The progress of this operation can be seen by aid of 
the yellow light, keeping the eyes close to the aperture behind. 

"When, from experience, the pictm-e is sufiiciently brought 
out, a little water is poured on the glass to wash off the deve- 
loping solution, and the cfrawing is partially fixed by the appli- 
cation of a small quantity of a solution of common salt. 

"The cfrawing may now be removed from the camera without 
fear of being injured by light, and the remainder of the opera- 
tions can be conducted outside the camera. 

"If the film is sufficiently strong to bear removal from the 
glass, the following procedure is adopted : — The plate of glass 
is placed horizontally upon the back lid of the camera, which 
is hrmg so as to form a temporaiy table, and the film is loosened 
from the edge of the glass with a flat strip of glass ; a sheet of 


damp paper is then placed flat on the drawing, and rather within 
its upper edge ; the film is turned over the edge of the paper, 
and a glass rod is placed just witliin the edge. The sheet of 
paper with the collodion in contact with it is now raised from 
the glass, and rolled ujj on the glass rod. When the drawing 
is entirely enclosed in the paper, the rod is removed, and the 
delicate film thus encased is put away into its proper receptacle, 
to be finally fixed and mounted at leisiu-e. 

''The drawing thus rolled up can be preserved for months 
without injmy, provided it is kept slightly damp ; and if each 
drawing is enclosed in another sheet of papei*, its preservation 
is stdl fm'ther secured. 

" The advantages of a camera of this kind may be thus enu- 

'•' It allows the preparation on the spot of the most sensitive 
surfaces ; their immediate use whilst the sensibility is at its 
maximum ; the ready development of the image, and after 

" All these operations being carried on consecutively, the 
operator can, after the first trial, see what residts the progress 
of his laboiirs is likely to produce. 

" It gives him the power of shading ofi" any portions of the 
view during the action of the light, by holding in front of the 
prepared plate and near the lens a movable screen, or any flat 
piece of wood, as the case may requii'e ; thereby preventing the 
too rapid action and consequent solarization of the distant por- 
tions of the scene. The spire of a church, for instance, pointing 
upwards into a bi-ight sky, often requires this precaution to 
prevent its being entirely lost. Other instances of this efiect will 
readily suggest themselves to those at all acquainted -sN-ith the art. 

" The camera can be made, with slight modifications, applicable 
to any other process on paper or glass, and of coiu'se obviates 
the necessity of any kind of portable tent." — Archer, F.S., 
Manual of the Collodion Photographic Process. 

The following figures represent JNIr. Archer's camera, as con- 
structed and improved by Mr. Griffin : — 

The figure 67 is a section of the camera, and 68 its external form, 
which, with a view to portability, is constnxcted so as to serve 
as a packing-case for the entire apparatus represented by figs. 
67 to 73. a is the sliding door that supports the lens h. c c are 
the side openings fitted with cloth sleeves to admit the operator's 
arms, c? is a hinged door at the back of the camera, which can 
be supported like a table by the hook e. f is the opening for 
looking into the camera during an operation. This opening is 
closed, when necessary, by the door g, which can be opened by 



the hand passed into the camera through the sleeves c. The 
yellow glass window which admits light into the camera during 

an operation is under the door h. i is the sliding feme for 
holdiiig the focusing glass, or the frame with the prepared glass, 

either of which is fastened to the sliding frame by the check k. 
The fi-ame slides along the rod I, I, and can be fixed at the proper 
focus by means of the step m. n is the gutta percha washing 



tray, o is an opening in the bottom of the camera near the 
door, to admit the well p, and which is closed, when the well is 
removed, by the door q. The well is divided into two cells, one 
of which contains the focusing glass, and the other the glass 
trough, each in a frame adapted to the sliding frame i. On each 
side of the sHdiug door that supports the lens a, there is, within 
the camera, a small hinged table r, supported by a bracket s. 
These two tables sei'\'e to support the bottles that contain the 
solutions necessary to be applied to the- glass plate after its ex- 
posure to the lens. 

Figs. 69 and 70 represent two cases, containing the various 
insti-uments and chemical preparations required for the coUodion 

process, a, fig. 69, is a grooved cell for a series of glass plates. 
6 is a receptacle for the lens of the camera, c contains a spii'it 
lamp ; d, a paii- of glass measures ; e, a porcelain pestle and 

mortar. The door / encloses a space containing a funnel with 
filter papers, and silks and leathei-s for cleaning the plates, g con- 
tains a small retort stand, a porcelain capsule, and a box with 
scales and weights. 



The case, fig. 70, Ls di^^.ded into two compartments. One 
side, a, contains twelve stoppered glass bottles, with the various 
chemical preparations required by the operator. The other side, 
which can be closed by the door h, contains a supply of photo- 
gi'aphic paper, both for negative and positive pictures. 

Fig. 71 is the glass trough for holding the nitra.te of silver 

71. 72. 

Fig. 72 is a fi-ame for fixing in the camera such plates of glass 
as do not require to be exposed to the lens while stUl in the 
glass trough. 

Fig. 73 is a pressure fi-ame for the preparation of positive from 
negative photographs. 

Fig. 74 is a section of this 

Both of these frames, figs. 72 
and 73, are so contrived as to 
be sidtable for plates of many 
different sizes. In the frame 
represented by fig. 72, the bars 
a and h are both movable, to 
permit the fixing of the plate 
in the camera directly opposite 
the centre of the lens. In the 
frame represented by fig. 73, 
the bar a alone is movable, and is fastened by screws that move 
in the slits h, h. 

The whole of these boxes and frames can be conveniently 
packed id the camera. The box, fig. 68, is passed lq by the 
side-door ; the well, p, and all the other cases and frames, by the 
door d; and the camera, thus loaded for transport, is put into a 
strong leather case. 



It has been proposed to use the bromide, instead of iodide of 
silver, in collodion. 

The most successful operator -with the bromodized collodion 
appears to have been M. Laborde, TS'ho communicated the fol- 
lowing as the results of his pi-actice to La Lumiere, French 
photographic joiuTial : — 

" I have studied the action of bromides by themselves and in 
combination vdth. collodion. My choice naturally fell upon 
those soluble in alcohol or ether, and I have tried the bromides 
of iron, nickel, cadmium, zinc, and mercury. The bromides of 
iron, nickel, and cadmiimi yielded the best restdts, and among 
these I give the preference to the bromide of cadmium. I have 
found it to possess so many advantages, that I have been several 
times tempted to banish all iodides ti'om my preparations. 
\5 gi-ains of bromide of cadmium, added to 1^ ounce (by weight) 
of solution of collodion, gives a liquid which may be used at once, 
and which has been kept for about five months, up to the pre- 
sent time, without perceptible change. Sidphate of iron, or 
pyrogallic acid, are used for developing j gallic acid produces but 
a veiy middling effect ; almost all the details of the image appeal" 
at once, the effect of the weakest radiations becomes sensible; 
but the extreme tints of the proof are not siitficiently different 
to allow of being printed 6-om with success. The following pro- 
cess is made use of to give them an actual value in this respect. 

" By adding a weak proportion of iodide of potassium to the 
bromide of cadmium the sensibility is increased, and we obtain 
at the same time a gi'eater difference between the extreme tints 
of the proof; the negatives are therefore superior. The follow- 
ing are the proportions usually employed : — 

Bromide of cadmium . . . . 12 grains. 
Iodide of potassium .... 0-.3 gi-ain. 
Collodion I5 ounce. 

" At first the iodide of potassium tinges the collodion with yel- 
lowish-red, but the bromide of cadmium by degrees removes this 
tint, and the solution becomes coloiu-less." 

Mr. W. Ci'ookes has lately commenced the investigation of 
these phenomena -^-ith a zeal and accuracy from wliich we may 
expect some important results. The following communication, 
made to the Photographic Society of London, will be read with 
interest : — 

" I have for some time past been working with bromized collo- 
dion, and as. from my expierience, it seems likely to become an 
agent of great value, perhaps the following accoimt of some ex- 
periments ■vs'ith it may prove of interest to any photographer. 


who lias tlie time and means at his disposal to investigate the 
subject more fully in its practical application. 

"To prepare the collodion I proceed as follows : — Mix together 
equal bulks of sulphuric acid, specific gravity 1 '80, and nitric acid, 
specific gravity 1 "50 ; stir well with a glass-rod, and then, while still 
warm, immerse as many pieces of good Swedish filtering-paper 
as the vessel will conveniently hold. Allow them to remain 
together for one houi' ; then poixr the liquid away, and wash the 
paper until free from the slightest ti'ace of acid, and allow it to 
dry in a warm room. 

" Take 8 drachms of the piu-est washed ether and ^ drachm 
of spirits of wine, 60° above proof and dissolve in this 6 grains 
of the above-prepared paper. This collodion may be bromized 
in the following manner : — In a small bottle place about 2 grains 
of crystallized nitrate of silver and about 10 grains of pure 
bromide of ammoniimi; pour on this 2 drachms of spirit 60° 
above proof, and allow them to remain together for some hours, 
shaking the mixtiu'e several times. One drachm and a half of 
the supernatant liquid are to be added to every ounce of the 
previously prepared collodion. Thus bromized, it will remain 
perfectly colourless and good for a long time. 

" I excite the j^late in a 30-grain silver bath, wliich has been 
previously satm-ated with bromide of silver ; about two minutes' 
stay in this bath is generally sufficient, though a little longer 
time does not injure it. The film of bromide of silver is a pale 
orange by transmitted and blvie by reflected light, and is very 
transj^areut. For developing, I prefer protonitrate of ii^on, 
being more accustomed to it, but have no doubt that in other 
hands pyrogallic acid woidd answer equally well. The above pro- 
jDortions of paper, alcohol, and bromizing compound may be 
varied within certain limits without much inflviencing the result. 
I have given the proportions which I am most in the habit of 
using, but would recommend that the experimentalist shoidd 
ascertain for himself whether a slight departure from the above 
proportions would give a collodion of the consistency and strength 
of that with which he is most accustomed to manipulate. 

" The chief advantages it seems to possess over the ordinary 
iodized collodion, besides its great sensitiveness, are the follow- 
ing. In a landscape the required opacity of the more strongly 
illiuninated parts (the sky, for instance) is not lost by over- 
exposiu'e; vegetation is also more easily copied. Its superior 
sensitiveness to colom-ed light is, however, most strikingly showTi 
when coloured glass or sulj)hate of quinine (as suggested by Sir 
John Herschel) is employed to absorb the strongly acting in- 
visible rays. To prove this, I arranged several flowers and 


plants with a view to obtain a great contrast of colom-, light, 
and shade. The best pictm-e I coixld obtain of them on iodized 
collodion was, as I had anticipated, wanting in half-tint, very 
few of the colours producing an adequate impression. When, 
however, bromized collodion was used imder the same cii'cum- 
stances, but with the interposition of the bath of sulphate of 
quinine, eveiy pai-t came out with nearly the same gradation 
and depth of hght and shade as existed in nature : this picture 
on bromized collodion behind the quinine bath requii'ed 40 
minutes ; on iodized, without the quinine solution, 4 minutes • 
but when I attempted to take a photogi-aph on iodized collodion, 
v/ith the quinine bath interposed, I fovmd that with the light I 
was working in, t)ie plate would not keep a sufficient length of 
time to enable me to obtain an image. 

"The advantages of using bromine in the place of iodine, for all 
objects having a green or vellow coloiu-,have been already pointed 



Section I. — ALBrjiEX ox Glass. 

In the Technologist for 1848, M. Niepce de Saint Victor pub- 
lished his mode of applying albumen to glass plates. M. Blan- 
quart Everard followed ; and successively albumen, gelatine, 
seram, and other animal substances, have been recommended 
for application on glass : but few of them have been found to 
answer so perfectly as albumen applied according to the direc- 
tions of M. Le Gray. 

He recommends that the whites of fresh eggs, equal to about 
five fluid ounces, be mixed with not more than 100 grains of 
iodide of potassiiyn, and about twenty grains of the bromide, 
and half that quantity of common salt. 

He then directs you to beat this mixture in a large dish ■n-ith 
a wooden fork, until it forms a thick white froth ; to let it repose 
all night, and the next day to decant the viscous liquid which 
has deposited, and use it for the preparation of your glasses. 

For this purpose take thin glass, or, what is much better, 
ground glass, on ichich the adherence is more per/ect ; cut it the 
size of your camera frame, and gi-ind the edges. 

The success of the proof is, in a great measure, due to the 
evenness of the coat of albumen. 

To obtain this, place one of your glasses horizontally, the 
unpoHshed side above (if you use ground glass, which I tliink 
preferable), and then 2)oiu' on it an abundant quantity of the 
albumen. Take a inile of glass, veiy straight, upon the ends of 
which have been fastened two bands of stout paper steeped in 
white wax : hold this with the fingers in such a manner that 
they will overlap the sides of the glass plate about one-eighth 
of an inch. You then di'aw the rule over the glass with one 
sweep, so as to take oflf the excess of albumen. The object of 
the sKp of paper is to keep the glass rxde from the siu'face of 
the plate, and insui-e a thin but even coating of the albuminous 

Thus, in making the paper band more or less thick, you vary 


the tMckness of tlie coating. Or you may arrive at the same 
i-esult by pasting two naiTow bands of paper on the sides of 
the plate, and passing simply the inile do^\'n. I prefer the fii-st 
means, because, with the second, one is almost sure to soil the 
glass in sticking on the paper. 

You must never go the second time over the glass with the 
i-ule, or you will make air bubbles. When thus prepared, per- 
mit the plate to diy spontaneously, keejiing it in a horizontal 
position and free from dust, ^^^len the coat of albumen is well 
dried, submit your glasses to the temperature of 160° to 180° 
Fahrenheit ; this you may do either before a quick fixe, or by 
shutting them up in an ii'on saucepan well tinned, with a cover ; 
you then place the saucepan in a bath of boiling water ; the 
action of the heat hardens the albumen ; it becomes perfectly 
insoluble, and ready to receive the aceto-nitrate of silver. 

The glass thus prepared may be kept for any length of time. 
I prepare the first coat also by satiu'ating the former mixtm-e 
with gallic acid, which gives it more consistency and gi-eater 

When you -wdsh to make a proof (Ijy using the preparation 
moist), you pkmge the glass thus prepared in a bath of aceto- 
nitrate of silver, described in the second ojieration of the 
negative paper. This operation is very delicate, because the 
least stoppage in its immei'sion in the bath will operate on the 
sensitive coating, and cause irregularities which nothing can 

To obtain this instantaneous and regular immersion, I make 
a box with glass sides, a trifle larger than the plate, and about 
half an inch vdde, ^vith wooden gi-ooves, similar to those in the 
Daguerreotype plate box : into this I poiu* the aceto-nitrate, 
and let the prepared glass fall into it with a single movement, 
leaving it to soak fom- or five minutes in the bath ; then remove 
it, wash well ^vith distilled water, and expose it in the camera 
while moist. The time will vary from two to thii-ty minutes, 
or nearly double that time if the glass is diy. 

When you wish to oj^erate "s\-ith the glasses dry instead of 
moist, it is proper to dip them in a bath of gallic acid a quarter of 
an hour after they are taken out of the aceto-nitrate bath ; then 
well wash them with distilled water, and chy them as dii-ected. 

When you take the plate out of the camera, you develope the 
image in the same way as the negative on paper, by putting it 
into a bath of satiu-ated gallic acid : when it is well developed, 
fix it by the same method indicated for the jxaper. 

To obtain a positive proof, it is sufficient to apply on the 
negative proof a sheet of common positive paper, or, better 


still, a sheet of the positive albuminized paper, which is pre- 
■viously described. 

You then put it in the pressure frame, placing above it a piece 
of black cloth pasted on one side of a thick sheet of glass ; 
then shut the frame, giving to the proof a slight pressure ; 
after which, expose it to the light. In order to follow its 
action you may just raise it by one corner of the glass, to judge 
of the tint which the image takes : when you think it sviffi- 
ciently exposed, take it out of the frame, and fix it the same as 
the positive paper. 

Niepce de Saint Victor has recently published a process in 
wliich he employs starch instead of albiimen on the glass plates. 
The main features of this process are as follows : — About 70 
grains of starch are rubbed down with the same quantity of 
distilled water, and then mixed Tvith three or foiu* ounces more 
water ; to this is added 5^ gi'ains of iodide of potassium dis- 
solved in a very small quantity of water, and the whole is boiled 
until the starch is properly dissolved. "With this the glass plates 
are carefidly covered, and then placed to dry on a perfectly 
horizontal table. When thoroughly dried, the aceto-nitrate of 
silver is applied by wetting a piece of paper, placing this on the 
starch, and over it another piece of paper wetted with distilled 
water. This mode of preparation furnishes, it is said, tablets of 
great sensibility ; but the starch is liable to bi-eak oflT from the 
glass, and there is much difficulty in spreading it uniformly in 
the first instance. 

Section II. — Mr. Malone's Process. 

Some very ingenious experiments have been made by Mr. 
Malone, from whose communication the following remarks are 
quoted : — 

" To the white of an egg its own bulk of water is to be added; 
the mixtiu-e, beaten with a fork, is then strained through a 
piece of linen cloth, and preserved for use in a glass stoppered 
bottle ; then a piece of plate glass, cleaned with a solution of 
caustic potash, or any other alkali, is to be washed with water 
and di-ied with a cloth. When the glass is about to be used, 
breathe on it, and rub its sm-face with clean new blotting paper ; 
then, to remove the dust and fibres which remain, use cotton- 
wool, or a piece of new linen. Unless this latter, and, indeed, 
eveiy other precaution, is taken to prevent the presence of dust, 
the pictui-e will be fall of spots, produced by a greater absorp- 


tion of iodine (in a subsequent process) in those tlian in the 
sm-roimcling parts. 

"On tlie clear glass pour the albumen, inclining the plate 
fi'om side to side until it is covered ; allow the excess to iim 
ofl" at one end of the comers, keeping the plate inclined, but 
neai'ly vertical. As soon as the albumen ceases to drop rapidly, 
breathe on or warm the lower half of the plate ; the warmth 
and moisture of the breath "w-ill soon cause it to part with more 
of its albumen, which has now become more fluid : of course, 
care miLst be taken to warm only the lower half. Wiping the 
edges constantly hastens the operation. Until this plan was 
adopted, the coatings were seldom uniform ; the upper half of 
the plate retained less than the lower. When no more albumen 
mns do^\Ti, dry the plate by a lamp, or by a common fire, if the 
dust that it is inclined to impart be avoided. 

" The next operation is to iodize the plate. Dilxite pure 
iodine "svith dry white sand in a mortar, using about eqiial parts 
of each ; put this mixture into a square vessel, and place over 
it the albuminized plate, previoiisly heated to about 100° Fah. 
As soon as the film has become yellow in coloiu", resembling 
beautifully stained glass, remove the plate into a room lighted 
by a candle, or through any yellow transparent substance, yel- 
low calico for instance, and plunge it vertically and rapidly into 
a deep narrow vessel containing a solution of one hundi-ed gi-ains 
of nitrate of silver to fifty minims of glacial acetic acid, diluted 
with five ounces of distilled water. Allow it to remain until 
the transparent yellow tint disappears, to be succeeded by a 
milky-looking film of iodide of silver. Washing with distilled 
water leaves the plate ready for the camera. 

" It may be here noted that the plate is heated in iodizing for 
the purpose of accelerating the absorption of the iodine : an ex- 
posure to the vapoiu- for ten minutes, with a few seconds' im- 
mersion in the silver solution, has been found to be sufiicient." 

Hydi'ochloric acid, chlorine or bromine, may be used with 
the iodine to give increased sensibility to the plate. 

The plate is removed fi^-om the camera, and we poiu' over it 
a saturated solution of gallic acid. A negative Calotjqie image 
is the result. At this point previoiis experimentalists have 
stopped. We have gone fiu-ther, and find that by pouring upon 
the surface of the reddish brown negative image, diiring its 
development, a strong solution of nitrate of silver, a remarkable 
effect is produced. The brown image deepens in intensity imtil 
it becomes black. Another change commences — the image 
begins to grow lighter ; and finally, by perfectly natiu'al magic, 
black is converted into white, presenting the curious phenomenon 


of the cliange of a Talbotype negative into apparently a positive 
Daguerreotype, the positive still retaining its negative properties 
■when viewed by transmitted light. 

To fix the picture, a solution of one part of hyposulphite of 
soda in sixteen parts of water is poured upon the plate, and left 
for several minutes, until the iodide of silver has been dissolved. 
Washing in water completes the process. 

" The phenomenon of the DaguerreotyiDe," says Mr. Malone, 
" is in this case produced by very opposite agency, no mercury 
being present ; metallic silver here producing the lights, while in 
the Daguerreotype it produces the shadows of the pictiire. We 
at first hesitated about assigning a cause for the dull white 
granular deposit which forms the image, judging it to be due 
simply to molecular arrangement. Later experiments, however, 
have given iis continuous films of bright metallic silver, and we 
find the dull deposit becomes brilliant and metallic when bur- 
nished. It should be observed that the positive image we speak 
of is on glass, strictly analogous to the Daguerreotype. It is 
positive when viewed at any angle but that which enables it to 
reflect the light of the ray. This is one of its characteristics. 
It must not be confounded with the continuous film image which 
is seen properly only at one angle ; the angle at which the other 
ceases to exist. It is also curious to observe the details of the 
image, absent when the plate is viewed negatively by transmitted 
light, appear when viewed positively by reflected light." 

Section III. — M. Martin's Process. 

Mx". Mayall published a form of process, employed by M. Mar- 
tin, which differs in no essential particular from those already 
described ; but as involving some rdceties of manipulation, on 
which, the writer says, depends the perfection of his finished 
pictures, it is thought advisable to quote it. 

" First. The albumen of a fresh egg must be beaten into a 
snow-like mass with a bimch of quills, dropping into it ten drops 
of a saturated solution of iodide of potassium ; allow it to stand 
six hours in a j^lace free from dust, and moderately warm, — say 

" Second. A piece of hand-plate glass, eight inches by six, with 
the edges ground smooth, must be cleaned as follows : with a 
piece of cotton wool rub over both sides ^svith concentrated nitric 
acid, then rinse well with water, and dry. Stick a wafer on that 
side which I wUl now call the back, to maik it j pounce ujDon 


the face a moderate quantity of fine tripoli, moistened with a 
few th'ops of a concentrated solution of cai'bonate of potash ; 
then with a piece of cotton wool rub the surface briskly in circles 
for about five minutes ; then with chy tripoli ; then with clean 
cotton to clear away all the dusty particles. 

" Tldi'd. To the centre of the back stick a gutta percha ball, 
as a handle : strain the prepared albujnen through clean linen ; 
poxu' it gently into the centre of the cleaned side of the glass, 
keep it moving until the surface is entii-ely covered, mn it into 
the corners, and finally pour ofi" any excess at the four corners ; 
disengage the gutta j^ercha handle, and place the glass on another 
slab, that has been levelled l)y a spirit level, in a place perfectly 
free fi-om dust, and modei-ately warm. I will call this my iodo- 
alhuminized glass ; it will keep for any length of time, and may 
be prepared in daylight. 

" Fourth. To excite (a yellow shaded light only being used), 
dissolve 50 grains of niti-ate of silver in 1 ounce of distilled water 
and 120 grains of strong acetic acid ; pour the whole of this so- 
lution into a cuvette, or shallow porcelain dish, a little lai'ger 
than the glass plate ; place one end of the iodo-albviminized 
glass in the solution ; with a piece of quill support the upper 
end of the glass, and let it fall suddenly on to the solution, 
lifting it up and down for ten seconds ; take it out and place it, 
face upwards, in another dish, half filled with distilled water ; 
allow the water to pass over the suiiace twice ; take out the 
glass, rear it up to dry ; it is ready for the camera, and wdll 
keejj in tliis state ten days, — of course, shut up from daylight, 
in a moderately warm place, bvit never moist. The solution 
may be filtered into a black bottle, and will do again by now 
and then adding a few drops of acetic acid, and keeping it in the 
dark. Expose in the camera fi-om four- to ten minutes, accord- 
ing to the amount of light and the aperture of the lens. Sup- 
pose I say a lens of thi-ee inches diameter, sixteen in focus for 
parallel rays, a one inch diaphragm placed thi-ee inches in front 
of the lens (one of Ross's photogi-aphic lenses is just the thing), 
the exposui'e woidd be in good light about five minutes. 

" Fifth. Develope as follows. Place the glass, face upwards, 
on a stand with adjusting sci-ews to make it level ; pom- a con- 
centrated solution of gallic acid over the siu'face ; the image ■wall 
be fi'om half an hoiu- to two houi-s in coming out. It is best to 
apply a gentle heat, not more than 10° above the temperature 
of the room, it being 60°. Should the image still be feeble, 
jjour off the gaUic acid, rinse the proof -with water, and pour on 
to it equal quantities of aceto-nitrate of silver and gallic acid 
reduced one-half with water. The image will now quickly de- 


velope ; arrest it in four or five minutes, -wash, it well in three 
waters, and fix with hyposulphite of soda as follows : — 

" Sixth. Three di-aclims of hyposulphite of soda to one ounce 
of water. Allow the proof to remaiu in this solution until all 
the yellow iodide disappears, wash it well, rear up to dry, and it 
is finished. 

" Success is sure to attend any one practising this method, 
provided the eggs are fresh and the glass is dean : if the glass is 
not clean, or the eggs are stale, the albumen will split ofi" in fixing. 

" Caution. — Wash all the vessels, as soon as done with, "with 
nitric acid, and then with water. Every precaution shoidd be 
used to avoid dust. The albumen of a duck's egg is more sensi- 
tive than that of a hen's ; and ii-om an experiment of to-day, I am 
almost certain that of a goose is more sensitive than either." — 
Athenceum, No. 1220. 

Section IV. — Miscella:nt:ous Modified Processes. 

Several other preparations have been employed, -n^th variable 
success, and recommended for procm-ing an absorbent film upon 
glass plates — amongst others, the sei-um of milk has been used 
by M. Blanqiiart Everai'd ; others combine with the albumen 
or gelatiue, grape sugar and honey ; the object of these being 
to quicken the process, which they appear to do in vu^tue of 
their power of precijiitating the metals from theii' solutions. 

Blanquart Everard has lately communicated the following to 
the Paris Academy of Sciences, as an instantaneous process : — 
"Fluoride of potassium, added to iodide of potassium, in the 
preparation of the negative proof, produces instantaneous images 
on exposm-e in the camera. To assiu'e myself of the extreme 
sensibility of the fluoride, I have made some experiments on the 
slowest preparations employed in photogi-aphy — that of plates 
of glass covered with albumen and iodide, requiring exposiu'e of 
at least sixty times longer than the same preparation on paper. 
On adding the fluoride to the albumen and iodide, and substi- 
tuting for the washing of the glass in distilled water after treat- 
ment with the aceto-nitrate of silver, washing in fluoride of po- 
tassium the image immediately on exposm-e in the camei-a ob- 
scura, I have indeed obtained this result (but imder conditions 
less powerfiil in their action) without the addition of the fluoride 
to the albumen, and by the immersion only of the glass plate 
in a bath of fluoride after its passage thi-ough the aceto-nitrate 
of silver. This projierty of the fluorides is calciUated to give 
very valuable results, and -will j^i'obably cause, in this branch of 


photographic art, a change equally as radical as that effected by 
the use of bromine on the iodized silver plates of Daguerre." 
A process published in the author's Researches on Liyht, in 
1844, and named the Fluorotype, sufficiently establishes my 
claim to priority in the use of the fluorides. 

Messrs. Ross and Thompson, of Edinburgh, hare been emi- 
nently successfid operators •with the albumen process. Many 
of theii- pictiu'es, which are of large size, exhibiting more artistic 
effect than is jDroduced by any other jjhotogi-aphei's. Some of 
the positives produced are veiy fine. At the meeting of the 
British Association in that city, these gentlemen exhibited some 
positive images on glass plates : these were backed up with 
plaster of Paris, for the purpose of exalting the effects, which 
were exceedingly delicate and beautiftd. 

Messi-s. Langenheim, of Philadelphia, have, however, recently 
introduced into this coxmtry specimens, which they tenn Hyalo- 
types. These are positive picttu-es, copied on glass from nega- 
tives, obtained upon the same material. Theii- pecidiarity is 
the adaptation of them for magic-lantern slidei-s. The process 
by which they are prodiiced is not pul)lished, but judging from 
the effects obtained, the probabiHty is that a very slight vai-iation 
only from the processes described has been made. The idea is 
an exceedingly hapjiy one, as by magnifying those images which 
are of the utmost delicacy and the strictest fidehty, perfect re- 
flexes of nature are obtained. 

There can be no doubt but other means of coating glass with 
sensitive materials may be employed. Certainly the use of 
albumen is a ready method, but this medivun appears to interfei-e 
with the sensibility which it is so desii-al>le to obtain. As stated, 
by using combinations of iodine and fluorine salts, there is no 
doubt but the sensibility may be most materially improved, and 
we fijid many of the continental photographei*s using honey and 
grape sugar with much advantage. 

I would, however, venture to suggest that films of silver pre- 
cipitated fi'om the solution of the nitrate by gi"ape sugar, 
aldehyde, or gim-cotton dissolved in caustic alkali, upon which 
any change could be aftei-wards produced, appear to promise 
many important advantages. 

Section Y. — Positive Photographs from Etchings on Glass 


A very easy method of producing any number of positive 
photographs from an original design is in the power of every 


one having some sliglit ai-tistic talent. The merit of having 
suggested the process I am about to describe has been claimed 
by Messrs. Havell and Wellmore, and also by Mr. Talbot ; 
indeed, there appears no reason to doubt the originality of either 
of these gentlemen, Mr. Havell ha^'ing prosecuted his experiment 
in ignorance of the fact that Mr. Talbot had used the same 
means to diversify his photographic specimens. Mr. Talbot 
proposes that a plate of warmed glass be evenly covered with a 
common etching ground, and blackened by the smoke of a candle. 
The design is then to be made, by carefully removing from the 
glass all those parts which should represent the lines and shadows, 
and shading out the middle tints. It will be evident that the 
light passing through the uncovered parts of the glass, and being 
obstructed by the covered portions, will impress on the white 
photographic papers a correct picture, having the appearance of 
a spirited ink di'awing. 

Mr. Havell's method was to place a thin plate of glass on the 
subject to be copied, upon which the high lights were painted 
with a mixture of white lead and copal varnish, the proportion 
of varnish being increased for the darker shading of the picture. 
The next day Mr. Havell removed, with the point of a pen- knife, 
the white ground, to represent the dark etched lines of the original. 
A sheet of prepared paper having been placed behind the glass, 
and thus exposed to light, a tolerable impression was produced j 
the half tints had, however, absorbed too much of the violet rays, 
an imperfection which was remedied by painting the parts over 
with black on the other side of the glass ; if allowed to remain 
too long exposed to the sun's rays, the middle tints became too 
dark, and destroyed the effect of the sketch. Another method 
employed by Mr. Havell was to spread a groim^d composed of 
white lead, sugar of lead, and copal varnish, over a plate of glass, 
and having transfeiTed a pencil cb-awing in the usual manner, to 
work it out "with the etching point. 

Various modifications of these processes have been introduced 
by different artists, and they evidently admit of many veiy 
beautiful applications. When the etching is executed by an 
engraver, the photograph has all the finish of a delicate copper- 
plate engraving. The only thing which detracts from this me- 
thod of photography is, that the great merit of self-acting power 
is abandoned. 

Etchings upon collodion plates are now employed for printing 
from ; and several works, to be illustrated in this way, ai'e now 
in progress for publication in Scotland. 



A VERT short time after the publication of Mr. Talbot's processe.s, 
which I anxiously repeated with various modifications, I dis- 
covered a singular property in the iodide of potassium {hyclrio- 
date of potash) of again whitening the paper darkened by ex- 
posui'e, and also, that the bleaching process was very much 
accelerated by the influence of light. Early in the year 1839, 
Lassaigne, Mr. Talbot, Sii- John Herschel, and Dr. Fyfe appear 
to have fallen on the same discovery. 

As this process, giving by one operation pictures with their 
lights coiTect is of much interest, I gave it for a very con- 
siderable time my undivided attention. The most extraordinary 
character of these salts is, that a very slight difference in the 
strength of the solutions, in the composition of the photographic 
paper, or in the character of the incident light, produces totallv 
opposite effects ; in one case the paper is rapidly whitened, in the 
other a deep blackness is produced almost as rapidly. Sometimes 
these opposing actions are in equilibrium, and then the paper 
continues for a long time perfectly insensible. 

I am inclined to hope these researches have reduced to cer- 
tainty their somewhat inconstant effects, and rendered this 
method of producing photographs one of the most easy, as it is 
the most beautiful. That the various positions I wish to estab- 
lish may be completely understood, and to insure the same re- 
sults in other hands, it will be necessary to enter into a somewhat 
detailed account of the various kinds of paper used, and to give 
tolerably full directions for successfully using them, either in the 
camera, or for dx-amngs by application, — to examine attentively 
the effects of different organic and inorganic prepai-ations on the 
paper, and to analyze the influence of the diflerent rays upon it. 
See also Part I., Chapter VI., Section VIL, page %'2. 


These particulars will be copied chiefly from my paper, "On 
the Use of the Hych-iodic Salts as Photogi-aphic Agents," pub- 
lished in the London and Edinburgh Philosophical Magazine for 
September and October 1840, to which will be added the results 
of my experiments since that time. 

The variable texture of the finest kinds of paper occasioning 
irregularities of imbibition, is a constant source of annoyance, 
deforming the di*a. wings -wdth dark patches, which are very difficult 
to remove : consequently my first endeavoiu-s were directed to 
the formation of a sm"face on which the photographic prepara- 
tions might be spread with perfect vmiformity. 

A variety of sizes were used with very uncertain residts. 
Neax'ly all the animal glutens appear to possess a colorific j^ro- 
perty, wliich may render them available in many of the negative 
processes ; but they all seem to protect the darkened silver from 
the action of the solutions of the iodides. The giims are acted on 
by the nitrate of silver, and browned, independent of light, which 
browning considerably mars the efiect of the finished picture. 
It is a singular fact, that the tragacanth and acacia gums render 
the pictiu'es pi'oduced much less pei-manent. I therefore found 
it necessary for general practice to abandon the use of all sizes, 
except such as enter into the composition of the paper in the 
manufactiu'e. It occvirred to me that it might be possible to 
saturate the paper with a metallic solution, which should be of 
itself entirely uninfluenced by light, on which the silver coating 
might be spread without suffering any material chemical change. 
The results beiag curious, and illustrative of some of the pecu- 
liarities of the process, it will be interesting to study a few of 

Sulphate and Muriate of Iron These salts, when used in 

small proportions, appeared to overcome many of the fii-st diffi- 
culties, but all the dramugs on papers thus prepared faded out 
in the dark. If, after these photographs have faded entirely out, 
they are soaked for a short time in a solution of the ferrocyanate 
of potash, and then are exposed to the light, the pictm^e is re- 
vived, but with reversed lights and shadows. 

Acetate and Nitrate of Lead.— These salts have been much 
used by Sir John Herschel, both in the negative and positive 
processes, and, it ajipears, Avith considei'able success. I found a 
tolerably good result when I used a saturated solution ; but 
papers thus pi-epared required a stronger light than other kinds. 
When I used weaker solutions, the drawings were covered with 
black patches. On these a little fm-ther explanation is requu-ed. 
When the strong solution has been used, the iodine which has 
not been expended in forming the iodide of silver — which form 


the liglits of the picture — goes to form the iocli Je of lead. This 
iodide is soluble ia boiling water, aud is easily removed from the 
paper. When the weaker solution of lead has been used, instead 
of the formation of an iodide, the hydriodate exerts one of its 
peculiar functions in producing an oxide of the metal. 

Muriate and Nitrate of Copper. — These salts, in any quantities, 
render the action of the iodides very quick ; and, when used 
in moderate proportions, they appeared to promise at first much 
assistance in quickening the process. I, have obtained, with 
papers into the preparation of which nitrate of copper has 
entered, perfect camera views in ten minutes ; but experience 
has proved their inapplicability, the edges of the parfs in shadow 
Ijeing destroyed by chemical action. 

Chlorides of Gold and Platinum act shnilarly to each other. 
They remain inactive until the pictui'e is formed ; then a rapid 
oxidation of these metals takes place, and all the bright parts of 
the j)ictiu'e are darkened. 

An extensive variety of preparations, metallic and non-metal- 
lic, was used with like effects, and I am convinced that the only 
plan of obtaining a pei-fectly equal svu-face, without impairing 
the sensitiveness of the paper, is careful manipulation with the 
ordinaiy muriates and silver solutions. 

By attention to the following dii-ections, which are simple in 
theii' character, but arrived at by a long series of inquiries, any 
one may prepare photographic papei-s on which the bleaching 
solutions shall act with perfect uniformity. 

The kind of paper on which the sUver is spreatl is an object of 
much importance. A paper kno^vn to stationers as satin post, 
double-glazed, bearing the mark of J. Whatman, Tiu-key MUl, is 
decidedly superior to every other kind I have tiied. The dark 
specks which abound in some sorts of paper must be avoided, 
and the spots made by flies very carefully guarded against. 
These are of small consequence dming the darkening process, but 
when the bleaching wash is applied, they form centres of chemi- 
cal action, and the bleaching process goes on around them, inde- 
pendently of light, deforming the cb-awing with small rings, 
which are continually extending theii' diameters. 

The Solution of Silver. — Take of cxystallized nitrate of silver 
120 grains, distilled water 12 fluid ch-achms; when the salt is 
dissolved, add of alcohol 4 fluid ch-achms, which rendei's the 
solution opaque ; after a few hoiu's, a minute quantity of a dark 
powder, which ajipeai's to be an oxide of silver, is deposited, and 
must be sepai-ated by the filtei'. The addition of the alcohol to 
the solution was adopted from an observation I made of its in- 
fluence in retarding the chemical action, which goes ou in the 


shade, of the hydriodates on the salt of silver. Its use is, there- 
fore, to make the action depend more on luminous influence, 
than would be the case without it. 

Nitric Ether. — Sweet spirits of nitre not only checks the 
bleaching process in the shade, but acts with the iodine salts to 
exalt the oxidation of the silver, or increase the blackness of it. 
In copying lace or any fine linear object, it is a very valuable 
agent; but it is useless for any other pui-poses, as all the faintly- 
lighted parts are of the same tint. 

Hydrochloric Ether, used as the solvent of the silver, and 
applied without any saline wash, has a similar property to the 
nitric ether ; but as it is readily acted on by faint light, it is of 
greater value. However, papers prepared with it must be used 
within twenty-fovir hoiu's, as they quickly lose their sensitive- 
ness, and soon become nearly useless. 

To fix with any degree of certainty the strength of the solu- 
tion of the salts which will in all cases produce the best effects, 
appears impossible ; eveiy variety of light to which the paper has 
been exposed to darken, reqvdiing a solution of diSerent specific 

In darkening these papers, the directions given at page 83 
should be strictly followed. 

Any' of the following preparations may be employed as the 
bleaching agents. 

Iodides of Potassium and Sodium. — The former of these salts 
being more easily procured than any other, is the one generally 
employed. The strength of the solution of these salts best 
adapted for the general kinds of paper is tliu-ty grains to an 
ounce of water. The following results will exhibit the difierent 
energies manifested by these solutions at several strengths, as 
tried on the same paper by the same light : — 

120 graiQS of the salt to an ounce of water took ) , f, . , 


to whiten the paper 











do. • 

■• do. 

































10 do. do. to do. 12 do. 

The other salts correspoud nearly with these in their action; 
a certain point of dilution being necessary with all. 

Iodide of Ammonia, if used on unsized paper, has some ad- 


vantage as to quickness over the salts either of potash or of soda. 
This preparation is, however, so readily decomposed, that the 
sLze of the paper occasions a libemtion of iodine, and the conse- 
quent foi-mation of brown-spots. 

Iodide of Iron.— This metallic iodide acts with i-apidity on the 
darkened paper ; but even in the shade its chemical energy is 
too great, destroying the shai-pness of outline, and impairing the 
middle tints of the drawing. It also renders the paper veiy 

Iodide of Mang'anese answers remarkably well when it can be 
prociu-ed absolutely free of iron. When the manganesic solution 
contains iron, even in the smallest quantities, light and dark 
spots are formed over the pictui-e, which give it a curious speckled 

Iodide of Baritun possesses advantages over eveiy other simple 
iodine solution, both as regards quickness of action and the 
sharpness of outline. A solution may, however, be made still 
superior to it, by combining a portion of iron with it. Forty 
gi-ains of the hydriodate of baryta being dissolved in one ounce 
of distilled water, five grains of very piu'e sulphate of iron 
should be added to it, and allowed to dissolve slowly. Sulphate 
of baryta is precipitated, which should be separated by filtration, 
when the solution is composed of iodide of barium and iron. 
By now adding a drop or two of diluted sulphuric acid, more 
baryta is precipitated, and a portion of hydriodic acid set free. 
The solution must be allowed to stand until it is clear, and then 
carefully decanted off fi-om the secUment, as filtering paper de- 
composes the acid, and free iodine is liberated. By this means 
we procure a photographic solution of a very active character. 
It should be prepared in small quantities, as it suffers decomposi- 
tion \inder the influences of .the atmosphere and light. 

Hydriodic Acid, if used on paper which wiU not decompose 
it, acts veiy readily on the darkened silver. A portion of this 
acid, free La any of the solutions, most materially quickens the 
action. From the barytic sokition it is always easy to set 
free the required portion, by precipitating the barytes by sul- 
phuric acid. As the iodide of bariiim is rarely kept by the retail 
chemist, it may be useful to give an easy method of preparing 
the solution of the required strength. 

Put into a Florence flask one ounce of iodine, and cover it 
with one fluid ounce and a half of distilled water ; to this add 
half a drachm of phosphorus cuff into smal pieces ; apply a very 
gentle heat until they imite, and the liquid becomes colourless ; 
then add another fluid ounce and a half of water. It is now a so- 
lution of hydriodic acid and phosphoric acid. By adding carbon- 


ate of barytes to it, a pliosphate of baiytes is formed, wliich, 
being insoluble, falls to tbe bottom, whilst tbe soluble iodide of 
barium remains dissolved. Make up the quantity of the solu- 
tions to nine ounces with distilled water, and carefully preserve 
it in a green glass stoppered bottle. 

For di-awings by application, less care is required than for the 
camera obscura. With a very soft flat brush apply the solution 
on both sides of the prepared paper, until it appears equally ab- 
sorbed; place it in close contact Avith the object to be copied, 
and expose it to sunshine. The exposure should continue until 
the parts of the paper exposed to uninterrupted light, which first 
change to a pale yellow, are seen to brown a Little. The obser- 
vance of this simple rule will be found of very gi-eat advantage 
in practice. Immersion for a short time in soft water removes 
the broAvn hue, and renders the bright j)arts of the pictiu-e 
clearer than they would be otherwise. 

Engravings to be copied by this process — which they are 
most beautifully — should be soaked in water and superimposed 
on the photographic papers, quite wet. If the jjaper is intended 
to be used in the camera, it is best to soak it in the bleaching 
solution until a slight change is apparent, from chemical action 
on the silver : it is then to be stretched on a slight fi\ame of 
w-ood, which is made to fit the camera, and not allowed to touch 
in any part but at the edges ; placed in the dark chamber of the 
camera at the proper focus, and pointed to the object of which a 
copy is requii-ed, which with good sunshine is eSected in about 
twenty minutes, varying of course with the degree of sensibility 
manilested by the jjaper. If the wetted paper is placed upon 
any porous body, it will be found, owing to the capillary com- 
munication established between difierent points, that the solu- 
tion is removed from some parts to others, and different states 
of sensitiveness induced. Another advantage of the frame is, 
the paper being by the moistiu'e rendered semi-transparent, the 
Light penetrates and acts to a greater depth ; thus cutting out 
fine lines which would otherwise be lost. However, if the 
camera is large, there is an objection to the frame; the solution 
is apt to gather into drops, and act intensely on small spots, to 
the injury of the general effect. When using a large sheet, the 
safest course is to sj)read it out when wetted upon a piece of 
very clean ivet glass, great care being taken that the j^aper and 
glass are in close contact. The pictm'e is not formed so quickly 
when the glass is used, as when the paper is extended on a frame, 
owing to the evaporation being slightly retarded. The addi- 
tional time requii-ed — about one-sixth longer — is, however, in 
most cases, of little consequence. 


The picture being formed bj tbe influence of sunshine, it is 
required, to render it unchangeable by any fiui.her action of the 
luminous fluid, not only that the salt of iodine be entu-ely re- 
moved from the paper, but that the iodide of silver which is 
formed be also dissolved out of the di'awing. 

By vreR washing the drawing in wann water, the iodide of 
potassium is removed, and the pictures thus prepared have been 
stated to be permanent j and if they are. kept in a portfolio, and 
only occasionally exposed, they are really so : for I shall show 
jDresently, that tney have the property of being restored in the 
dark to the state in tohich they zvere jjrior to the destructive action 
of light. A drawing which I executed in June, 1839, which has 
often been exposed for days successively to the action of sunshine, 
and has altogether been very little cared for, continues to this 
date (December, 1853) as perfect as at fii-st. These photogTaphs 
vnl\ not, however, bear long-continued exposure without injiuy 
— about three months in summer, or six weeks in winter, being 
sufficient to destroy them. As this gradual decay involves some 
very cm'ious and interesting chemical phenomena, I shall make 
no excuse for dwelling on the .suljject a little. 

The di'awing fades first in the dark parts, and as they are per- 
ceived to lose their definedness, the lights are seen to darken, im- 
til at last the contrast between light and shadow is very weak. 

If a dark paper is washed \ an iodide in solution, and ex- 
posed to sunshine, it is fii'st bleached, becoming yellow ; then the 
light again darkens it. If, when quite dry, it is carefully kept 
from the light, it will be found in a few days to be again restored 
to its original yellow colour, which may be again darkened by 
exposiu-e, and the yellow colom- be again restored in the dark. 
The sensitiveness to the influence of light diminishes after each 
exposiu'e, but I have not been enabled to arrive at the point at 
which this entfrely ceases. If a dark paper, bleached by an 
iodide and light, be again darkened, and then jilaced in a 
bottle of water, the yellow is much more quickly restored, and 
bubbles of gas will escape freely, which will be found to be 
oxygen. By enclosing pieces of iodized paper in a tube to 
darken, we discover, as might have been expected, some hydro- 
gen is set free. If the paper is then well (fried, and carefrilly 
shut up in a warm dry tube, it remains dark ; moisten the tube 
or the papei", and the yellowness is speedily restored. 

Take a photogi-aph thus formed, and pla-ce it in a vessel of 
water: in fxfew clays it wiU fade out, and bubbles of oxygen mil 
gather around the sides. If the water is examined there vnW be 
found no ti-ace of either silver or iodine. Thus it is evident the 
action has been confined to the paper. 


We see that the iodide of silver has the power of separating 
hydrogen from its combinations. I cannot regard this singvJar 
salt of silver as a definite compoviud : it appears to me to com- 
bine ^vith iodine in uncertain proportions. In the process of 
darkening, the liberation of hydrogen is certain; but I have not 
in any one instance been enabled to detect free iodine : of course 
it must exist, either in the darkened surface, or in combination 
with the unaffected under layer : possibly this may be the iodide 
of silver, with iodine in simple mixture, which, when light acts 
no longer on the preparation, is liberated, combines with the 
hydrogen of that portion of moisture which the hygrometric 
nature of the paper is sure to furnish, and as an liydriodate again 
attacks the darkened surface, restoring thus the iodide of silver. 
This is strikingly illustrative of the feding of the photograph. 

The picture is formed of iodide of silver in its light parts, and 
oxide of silver in its shadows. As the yellow salt darkens under 
the influence of light, it pai-ts with its iodine, which immediately 
attacks the dark oxide, and gradually converts it into an iodide. 
The modus oi^erandi of the restoration which takes place in the 
dark is not quite so apparent. It is possible that the active 
agent being quiescent, the play of affinities comes undistiu-bed 
into operation; that the dark j^arts of the picture absorb oxy- 
gen from the atmosphere, and restore to the lighter portions the 
iodine it has before robbed them of A series of experiments 
on the iodide of silver in its pure state will still more strikingly 
exhibit this very remarkable peculiarity. 

Precipitate with any iodide, silver, from its nitrate in solution, 
and expose the vessel containing it, liquid and all, to sunshine; 
the exposed surfaces of the iodide will blacken : remove the 
vessel into the dark, and, afier- a jew liours, all the blackness "will 
have disappeared. We may thus continually restore and remove 
the blackness at pleasure. If we wash and then well dry the 
precij)itate, it blackens with difficulty, and if kept quite diy it 
continues dark ; but moisten it, and the yellow is restored after 
a little time. In a watch-glass, or any capsule, place a little 
solution of silver ; in another, some solution of any iodine salt ; 
connect the two with a filament of cotton, and make up an elec- 
tric circuit "with a piece of platina "wire : expose this little ar- 
rangement to the light, and it will be seen, in a veiy short time, 
that iodine is liberated in one vessel, and the yellow iodide of 
silver formed in the other, which blackens as quickly as it is 

Place a similar arrangement in the dark ; iodine is slowly 
liberated. iVo iodide of silver is formed, but around the "wire 
a beautiful ciystallization of metallic silver. Seal a piece of 


platina wire into two small glass tubes ; these, when filled, the 

one with iodide of potassium in solution, and the other with a 

solution of the nitrate of silver, reverse into two 

watch-glasses, containing the same solutions ; 

the glasses being connected with a piece of 

cotton. An exposui^e diu-ing a few hoiu-s to 

daylight will occasion the solution of the iodine 

salt in the tube to become quite bro^\Ti with 

liberated iodine : a small portion of the iodide 

of silver will form along the cotton, and at the 

end dipping in the salt of silver. During the 

night the liquid will become again coloui-less 75 

and transparent, and the dark salt along the 

cotton will resume its native yellow hue. 

From this it is evident that absolute permanence will not be 
given to these photographs until we succeed in remo\'ing from 
the paper all the iodide of silver formed. The hyposulphites 
dissolve iodide of silver; therefore it might have been expected, 
a 2>riori, they would have been successful on these cLrawings. If 
they are washed over with the hyposulphite of soda, and then 
quickly rinsed in plenty of cold water, the drawing is improved, 
but no better fixed than with cold water alone. If we persevere 
in using the hyposulphite, the iodide is darkened by combining 
with a portion of sulphur, and the lights become of a dingy 
yellow, which is not at all pleasant. 

No plan of fixing will be found more efficacious with this 
variety of photograjihic di-awings, than soaking them for some 
hours in cold water, and then well washing them in hot water. 

It often happens that a picture, when taken from the camera, 
is less distinct than could be desired : it should not, however, be 
rejected on that account. All the details exist, although not 
visible. In many cases the soaking is suificient to call them into 
sight ; if they cannot be so evoked, a wash of weak ammonia or 
muriatic acid seldom fails to bring them up. Care, howevei", 
must be taken not to use these preparations too strong, and the 
picture must be washed on the instant, to remove the acid or 

One very sing-ular property of these photographs is, that when 
first prepared, and after the w^ashing, they are not fixed or other- 
wise ; but when exposed to sunsliine, they change in their dark 
parts from a red to a black. This peculiarity will be found by 
experiment to be entirely dependent on the influence of the red 
rays, or that poi-tion of the sunbeam which appears to have the 
greatest heating power : hence regarded as the seat of greatest 
calorific power. 


I have before mentioned the peculiar state of equilibrium in 
which the paper is when wetted -with the hydriodate, and that a 
slight difference in the incident light will either bleach or 
blacken the same sheet. If fovu- glasses, or coloured fliiid.s, be 
prepared, which admit respectively the blue, green, yellow, and 
red rays, and we place them over a paper washed with some 
solution of an iodide having an engraving superposed, it ^^-ill be 
bleached under the influence of the blue light, and a perfect 
jiicture produced ; while, under the rays transmitted by the 
green glass, the drawing will be a negative one, the paper having 
assumed, in the parts which represent the lights, a very defined 
blackness. The yellow light, if piu'e, will produce the same effect, 
and the red light not only induces a like change, but occasions 
the dark pai-ts of the engraving to be represented in strong 
lights: this last pecidiarity is dependent on the heating i^ays, 
and oj)ens a wide field for inquuy. My point now, however, is 
only to show that the darkening of the finished photogi'aph is 
occasioned by the least refrangible rays of light; whereas its, 
preparation is effected by the most refrangible. 

I know not of any other process which shows, in a way at 
once so decided and beautiful, the wonderful constitution of every 
sunbeam which reaches us. Yet this is but one of numerous 
results of an analogous character, produced by these opposite 
powers, necessary to the constitution of that solar beam, which 
is poured over the eai-th, and effects those various changes which 
give to it diversified beauty, and renders it conducive to the 
well-being of animated creatiu-es. 

Before quitting this branch of the art, it will be interesting to 
examine the modifications which have been introduced by some 
continental inquii-ei's. 

M. Lassaigue, who has claimed priority in the use of the 
iodide of potassium, satiu-ated his paper with a sub-chloride of 
silver, which was allowed to assume a violet-bro^vn coloxu", and 
it was then imjjregnated with the iodidated solution. 

M. Bayard simply allowed ordinary letter jiajDcr, prepared 
according to Mr. Talbot's method, to blacken by light. He 
then steeped it for some seconds in a solution of iodide of 
potassiiim, and laying it on a slate he placed it in the camera. 

M. Verignon introduced a somewhat more complicated pro- 
cess. His dii^ections are — ^White paj^er should fii'st be washed 
with water acidulated by hydi'ochloric (muriatic) acid ; then, 
after being well diied, steeped in the following solution : — "Water 
foiu'teen parts, with one part of a compound formed of two 
parts of muriate of ammonia, two parts of bromide of sodium, 
and one of chloride of strontium. The paper cbied again is 


passed into a veiy weak sohition of niti-ate of silver. There is 
thus fomied, by double decomposition, a chloride and bromide of 
silver, which is made to tmii black by exposing the paper to the 
light for about half an horn-. To use this paper, it is steeped in 
a very weak solution of the iodide of sodium, and placed, quite 
wet, into the camera obscura, at the proper focus. In fine 
weather, M. Verignon states, the efiect is produced in twelve 
mi unites. I have, however, never produced a good picture by 
this process in less than thirty minutes. A great objection to 
this mode of preparation is the very rapid deterioi-ation of the 
paper: every day it will become less and less sensitive to light, 
and at the end of a fortnight it is useless. 

The papei's recommended for use in the former pages have the 
advantage of keeping well, jirovided ordinaiy care is taken with 
them. It is necessary to exclude them from the Hght, to keep 
them very dry, and, as much as possible, they should be pro- 
tected fi-om the action of the air. I have kept papei-s, prepared 
with the muriate of ammonia, baryta, and strontia, for twelve 
months, and have foimd them but very little impaired. 

Dr. Schaf haeutl allows jDaper prepared in the way mentioned 
at a former page to darken in a bright sun-light. It is then 
macei'ated for at least half an horn', in a liquid prepared by 
mixing one part of the already described acid nitrate of mercury, 
vrith. nine or ten pai-ts of alcohol. A bright lemon yellow 
precipitate of basic hyponitrate of the protoxide of qviicksilver 
falls, and the clear liquor is preseiwed for use. The macerated 
paper is removed fi'om the alcoholic solution, and quickly di-awn 
over the surface of diluted muriatic acid (one part strong acid to 
seven or ten of water), then quickly washed in water, and 
slightly and carefidly dried at a heat not exceeding 212° of Fahr. 
The paper is now ready for being bleached by the rays of the 
Sim ; and in order to fix the ch-awing, nothing more is required 
than to steep the pajoer a few minutes in alcohol, which dissolves 
the fi-ee bichloride of mercmy. I must confess, however, that 
in my hands the process has not been so successful as it is 
described to have been by the author. 

It is perhaps necessaiy to remark, that we cannot multiply 
designs from an original bleached photograph. The yellow 
coloiu- of the paper is of itself fatal to transfers, and independently 
of this, the wet hychiodic sohition would immediately destroy 
any superposed photogi-aph. 

\Ye have seen in a former chapter that the white photographic 
papei-s are darkened by the blue, indigo, and violet rays. On 
the dark papers washed with the iodine salts in solution, the 
bleaching is effected most energetically by the violet rays : it 



proceeds "w-itli lessening intensity to the blue, while aU the rays 
below the yellow have a darkening iuiluence on the paper. This 
effect will be best illustrated by figiu'e 76, in which is shown — 
somevsrhat exaggerated for the sake of distinctness — the very 
remai'kable action which takes place : cleai-ly establishing the fact 
first noticed by "VTollaston, that the two extremities of the 
spectrum have different powei*s. 

The remarkable manner in which the point of greatest inten- 
sity is shifted from the blue to the violet, when papers have 
but a very slight difference in their composition or mode of 
preparation, is an extremely ciu-ious point of philosophical 



Violet. . 

Indigo . 

Green. . 

inqmiy. It vnll be evident from what has been said, that it is 
necessary the focus of the \iolet rays shoidd be always chosen 
in using these papers in the camera. 




These remarks "will apply vritli equal force to all the processes 
by wkich -views of external objects can be obtained; but tbey 
have more especial reference to those highly sensitive ones, the 
Daguerreotype, the Talbotype, and the Collodion processes. 

It has ah-eady been stated 
that a single achromatic 
lens, producing a large 
image, should be employed 
for motionless obj ects, "where 
time is not of consequence. 
For a building, a statue, or 
the like, it is not of much 
consequence whether one 
minute or ten may be con- 
sumed ia the operation of obtaining its impression. With the 
human figure and animals the case is very diflFerent : the utmost 
concentration of the solar radiations is therefore required to 
insure rapidity of action. This is effected by the double combi- 
nation of lenses, which are usually moimted 
and adjusted as shown in the above fig- 
ure, 77. In fig. 78, the mounting of the 
single lens arrangement is shown. 

It is often of the utmost importance, to 
obtain definition of the objects, that aU 
extraneous rays should be cut ofi"; this 
is efiected by means of a diaphragm of 
stops, which can be obtained to fit any 
lens. With this adjustment any sized aperture can be obtained. 

Section I. — Buildings, Statues, Landscapes, and Foliage. 

The great defect ia nearly all the photographic pictiires which 
are obtained is the extreme conti-ast between the high lights and 


the shadows, and in many an entii'e absence of the middle tones 
of the pictiu'e. 

In the very beautiful productions of Mr. Buckle, of Peter- 
borough, which were displayed in the Great Exhibition, there 
was a very remarkable degree of fine definition, united with a 
beautiful blending of the respective parts which constituted the 
picture. There was no glaring contrast between the lights. 
Those parts which were the most brilliantly ilkiminated were 
softened into the middle tones of the picture, and those again faded 
gradually into the deep shadows. In the works of M. Martin 
and M. Flacheron, whose processes I have given, the same har- 
monizing of lights and shadows was generally foimd to exist. 

The usual mistake with amateui-s is that of selecting bright 
sunshine as the pex'iod for operating. It is thought, when a 
cathedral, for example, is brilliantly lighted up by svmshine, is 
the time for obtaining a photographic copy of it. A little i-eflec- 
tion will convince the operator that this is the case only under 
particular conditions. 

"When the projecting parts of the building are flooded with 
sunshine, they cast the deepest possible shadows ; consequently, 
in the photogi-aphic picture the pi-ominent points would appear 
brilliantly white, and the shadows intensely dark. 

It will be understood that I refer always to the positive, or 
completed picture. 

A clear blue sky, reflecting its light upon a similar structure, 
produces less prominent illumination of the bold ornamental 
parts, and gives more light to those pai-ts on which the shadows 
are cast. A photograph taken imder such conditions of light 
and shade will l)e far more beautiful than the spotted productions 
which ordinarily result from the practice of operating when the 
sun is shining brightly on the object. 

In the same manner, when the sim shines brightly on the 
leaves of trees, a very large quantity of light is reflected from 
their surfaces, the other parts appearing by contrast in almost 
absolute shadow. Hence, nearly all photographic views of 
forest scenery have moi'e the appearance of scenes which have 
been sprinkled with snow than foliage glowing with sunshine. 

An artist studies in his productions the most efiective dis- 
position of the lights and shadows, and it is by the harmonious 
disposition of these that he succeeds in gi\dng a peculiar charm 
to his productions. Nearly all photographic pictures, although 
they have the merit of strict truthfulness, appear to want this 
great beauty of art. This has mainly arisen from the circumstance 
that intense illumination has been sought for under the idea of 
producing the sharpest picture ; and it is true that thus we do 



obtain a very perfect definition of outline. Many productions 
are remarkable for tbis, and, indeed, reproduce witb unnaturiil 
exactness all tbe minute details of tbe objects copied; wbereas 
the human eye never sees this extraordinary sharpness of out- 
line in nature ; upon the edges of every object there are fringes 
of light which soften off theii* outlines, and subdue the general 
tone of objects, blending all harmoniously. Perhaps there is 
more than ordinary difficulty in producing this in a representa- 
tion of nature which is effected by means of a lens. The artist 
may, however, do much : all times, even of bright illumination, 
are not fitted for producing a picturesque photogTaph. Natm-e 
should therefore be looked at with an artist's eye, and the happy 
moment chosen when the arrangements of light and shade give 
the most pictiu-esque effects, and when these are in a condition 
to be correctly rejiroduced according to the laws by which actinic 
influences are regulated. 

Section II. — Portraits from the Life. 

It is important for the production of a correct likeness that 
as small an ai^erture as possible should be used. By doing this 
thei-e is great loss of Hght, and consequently the necessarily pro- 
longed time must be compensated for by greatly increased 
sensibility in the plates. 

It is also important that arrangements should be made to 
cut off from the lens all light proceeding from extraneous objects: 
this is best effected by the modes adopted by M. Claudet. 

The camera is placed, as shoT\Ti in section. Fig. 79, within an 
arrangement of ciu'tains which, as wiU be seen in the vignette 
heading to this part, page 175, is capable of adjustment, so as 



to have any required opening in front of the camera. The whole 
of this screen being mounted on rollers is easily moved ; there- 
fore the o2)erator has it in his power to adjust the opening, and 
to shut off all adventitiuos radiations, thus securing the effec- 
tiveness of the rays proceeding directly from the sitter, or the 
object to be copied. 

The sitter should be placed in the easiest 
possible jjosition compatible with the arrange- 
ment of the body as nearly as is possible in a 
vertical plane. This is necessary, as the parts which 
are nearest the glass suffer a very considerable 
degree of distortion and enlargement. Of course 
great steadiness is required on the part of the 
sitter during the few seconds he submits to the 
operation of the photogi-apher. It is usual to 
support the head by a rest fastened to the back of 
the seat, as shown in fig. 80 ; but where the person 
can maintain a steady position without this, the 
result is generally the most satisfactory, the "rest " 
not unfrequently giving an air of stiffness to the 
sitter. In a great number of 2:)ortraits a dark and 
unnatural shade is thrown under the eyes : this 
arises from the employment of a "top light." The 
light falling vertically produces the shadow of the 
brow over the eye, and gives a sombre character 
to the face. This is objectionable also, as beiug annoying to 
the sitter, who assumes in consequence a somewhat painful 

Those who have attended to the analyses of the spectmm, 
included in the second division of our subject, have become 
aware that the radiations from all coloured objects are not 
alike. A long description would not render this so apparent 
as a single illustration. The frontispiece represents, therefore, 
a group of flowers, including the three j^rimary colours, and a 
few comjDOund tints; an exact copy of a photograph taken from 
such a group is placed beneath it, and the result is shown. 
Hence it is of the utmost importance, particiUarly to ladies, that 
they should be dfrected to avoid in their dresses, when about to 
sit for their portraits, such colours as would produce darks for 
lights, and the contrary. 



Section III. — Photographic Pentagraph. 

In a letter to Sir Jolin Herschel, which was published in the 
Athencewm, ]Mr. Stewart directed attention to a means by which 
photographs could be readilv enlarged. The plan had been in 
operation amongst photographic artists for some time, but it was 
not usually adopted, and Mr. Stewart's Letter certainly brought 
it into general use. The folloAving is Mr. Stewai't's description 
of the requii'ed apparatus : — 

" One of my friends here, Mr. HeUmann, has lighted on an 
ingenious method of taking fi-om glass negatives positive impres- 
sions of different dimensions, and with all the delicate minute- 
ness which the negative may possess. This discovery is likely, 
I think, to extend the resom-ces and the application of photo- 
graphy, — and with some modifications, which I will explain, to 
increase the power of reproduction to an almost unlimited 
amoimt. The plan is as follows : — The negative to be reproduced 
is placed in a slider at one end («) of a camera or other box, 
constiiicted to exclude the light throughout. The surface pre- 
pared for the reception of the positive — whether albumen, col- 
lodion, or paper — is placed in another slider, as usual, at the op- 
posite extremity (c) of the box, and intennediately between the 
two extremities (at h) is placed a lens. The negative at a is 
presented to the light of the sky, care being taken that no rays 
enter the box but those traversing the pai^tly transparent nega- 
tive. These rays are received and directed by the lens at h upon 
the sensitive surface at c, and the impression of the negative is 
there produced with a rapidity proportioned to the light admit- 
ted, and the sensibility of the surface presented. By varj^ng 
the distances between a and c, and c and h, any dimension re- 
quired may be given to the positive impression. Thus, from a 
medium-sized negative, I have obtained negatives foiu- times 
larger than the orisinal, 

and other impressions re- "" * — 

duced thirty times, capa- 
ble of figuring on a watch- 
glass, brooch, or ring. 

"a, c. Slides to hold the 
frames containing the ne- 
cjative and the receiving 
surface for the positive. 

" h. Frame, with thelens. 


" e. Dotted lines, indicating the top of the box or frame. 
''f;f. Bottom board, or foundation of the same. 


" Undoubtedly one of the most interesting and important ad- 
vantages gained hj this sinqole arrangement is, the power of 
varying the dimensions of a picture or portrait. Collodion giving 
results of almost microscopic minuteness, such negatives bear en- 
larging considerably without any very percej)tible deterioration 
in that respect. Indeed, as regards portraits, there is a gain in- 
stead of a loss ; the power of obtaining good and pleasing like- 
nesses appears to me decidedly increased, the facility of subse- 
quent enlargement permitting them to be taken sufficiently 
small, at a sufficient distance (and therefore with greater rapidity 
and certainty), to avoid all the focal distortion so much com- 
plained of; while the due enlargement of a portrait taken on 
glass has the eflfect, moreover, of depriving it of that hardness of 
outline so objectionable in a collodion portrait, giving it more 
artistic effect, and this without quitting the perfect focal point, 
as has been suggested. 

" But there are many other advantages obtained by this process 
For copying by engraving, &c., the exact dimension requii-ed of 
any picture may at once be given to be copied from. 

"A very small photographic appai-atus can thus be employed, 
when a large one might be inconvenient or impracticable, the 
power of reproducing on a larger scale being always in reserve. 
Independent of this power of varying the size, positives so taken 
of the same dimension as the negative, reproduce, as will be 
readily undei'stood, much more completely the finer and more 
delicate details of the negatives, than positives taken by any other 
process that I am acquainted Avith. 

"The negative also may be reversed in its position at a, so as to 
produce upon glass a positive to be seen either upon or under the 
glass. And while the I'apidity and facility of printing are the 
same as in the case of positives taken on paper prepared with 
the iodide of silver, the negatives, those on glass particidarly, 
being so easily iujin-ed, are much better preserved, all actual con- 
tact with the positive being avoided. For the same reason, by 
this process positive impressions can be obtained not only upon 
wet paper, &c., but also upon hard inflexible substances, such as 
porcelain, ivoiy, glass, &c. ; and upon this last, the positives 
being transparent, are appHcable to the stereoscope, magic 
lantern, &c. 

" By adopting the following arrangement, this process may be 
used lai'gely to increase the power and speed of reproduction 
with little loss of eifect. From a positive thus obtained, say on 
collodion, several hundred negatives may be produced either on 
paper or on albimiinized glass. If on the latter, and the dimen- 
sion of the original negative is presented, the loss in minuteness 


of detail and harmony is almost imperceptible, and even wlien 
considerably enlarged, is so trifling as in the majority of cases to 
pi'ove no objection in comparison with the advantage gained in 
size, while in not a few cases, as already stated, the pictm^e ac- 
tually gains by an augmentation of size. Thus, by the simiil- 
taneous action, if necessary, of some hundreds of negatives, many 
thousand impressions of the same pictm-e may be produced in 
the course of a day. 

"I cannot but think, therefore, that this simple but ingenious 
discovery ^yill prove a valuable addition to oiu" stock of photo- 
graphic manipulatory processes. It happily turns to account 
and utilizes one of the chief excellencies of collodion — that ex- 
treme minuteness of detail which, from its excess, becomes almost 
a defect at times — toning it down by increase of size till the 
harshness is much diminished, and landscapes, always more or 
less un pleasing on collodion from that cause, are rendered some- 
what less dry and cmde. 

"A very Httle practice wdll suffice to show the operator the 
quality of glass negatives — I mean as to vigour and development 
— best adapted for repi'oducing positives by this method. He 
wnll also find that a gi'eat power of correction is obtained, by 
which overdone parts in the negative can be reduced and others 
brought up. Indeed, in consequence of this and other advan- 
tages, I have little doubt that this process will be very generally 
adopted in poi-trait-taking. 

" Should yoiu' old idea of preserving pubHc records in a concen- 
trated form on microscopic negatives ever be adopted, the imme- 
diate positive reprodiiction on an enlarged readable scale, without 
the possibility of injury to the plate, will be of ser^'ice." 



From the interest which this very interesting optical instm- 
ment has excited, and the very intimate relation which exists 
between it and photography, since it is ordy practical to produce 
images suited for the instrument by the agency of the camera 
obscura, it is thought advisable to devote a short chapter to 
some notice of it. It is not intended that any examination of 
the phenomena of vision, or of the application of the stereoscope 
to the explanation of single vision with a pair of eyes, shall be 
attempted ; these questions would be somewhat out of place in 
the present manual, and would occupy too large a space if pro- 
perly dealt with. 

The stereoscope is before the world : a simple description, 
therefore, of the forms under which it may be constructed, and 
a sufficient explanation of its principles, is all that can here 
with proj^riety find a place. The name is compounded from two 
Greek words, signifying solid, and / see, and adopted from the 
fact that two pictures on a plane surface will, when adjusted 
in the instrument, resolve themselves into one image, and that 
image will acquire an apparently distinct solidity, being repre- 
sented as an object having three dimensions, — length, breadth, 
and thickness. 

"The theory" — of single vision with a pair of eyes — says 
Mr. Wheatstone, in his valuable Memoir " On some remarkable 
and hitherto unobserved Phenomena of Binocular Vision," — 
" The theory which has obtained the greatest currency is that 
which assumes that an object is seen single because its pictures 
fall on corresponding points of the two retinte ; that is, on points 
which are similarly situated with respect to the two centres, both 
in distance and position. This theory supposes that the pictures 
projected on the retinre are exactly similar to each other, corre- 
sponding points of the two pictures falling on corresponding points 
of the two retinae." Leonardo da Vinci, in his Treatise on 
Painting, has some remarks on the peculiarity of vision, which 
bear in a singular manner on the phenomena of the stereoscope, 



to tlie effect, tliat a painting, though conducted with the greatest 
art and finish to the last perfection, both with regard to its con- 
tours, its lights, its shadows, and its colours, can never show a 
relievo equal to that of natiu'al objects, unless these be viewed 
at a distance, and with a single eye ; for if an object, as an orange, 
be viewed by a single eye, all objects in that space behind it, 
which we may suppose to be included in its shadow, are Ln\Tsible 
to that eye ; but open the other eye without moving the head, 
and a portion of these becomes visible : those only are hid from, 
sight which are included in the space covered by the two shadows 
formed by two candles supposed to be placed in the positions of 
the eyes. The hidden sr)ace is so much the shorter according to 
the smallness of the object, and its proximity to the eyes. Upon 
this Mr. Wheatstone remarks : — " Had Leonardo da Vinci taken, 
instead of a sjjhere, a less simple figure for the purpose of his 
illustrations — a cube for instaape — he would not only have per- 
ceived that the object obsciu-ed fi-om each eye a different part of 
tlie more distant field of view, but the fact would also have been 
forced upon his attention, — that the object itself presented a 
different ajjpearance to each eye." 

If any of my readers will be at the trouble to look at a 
simple solid form, keeping the head perfectly steady, with a single 
eye, and make an outline drawing of the image as seen — say, first 
with the left eye, and then with the right eye — it will be foimd 
that two dissimilar forms Avill be obtained analogous to those 
represented in the following diagi-am: — 


By a little effort, it is easy, by squinting, to resolve these two 
figures into one, when it will be foimd that an apparently solid 
image is formed from these dissimilar oxitlines of a solid. 

The stereoscope of Professor Wheatstone is arranged to pro- 
duce this in a more effective manner. The instrument, fig. 83, 
consists of two plane min-ors, so adjusted that their backs form 




an angle of ninety degrees with, eacii otlier. These mirrors are 
fixed by their common edge upon an horizontal board, in such a 

manner that, upon bringing it close to the face, each eye sees the 
image reflected from the two ends of the instrument in a difier- 
ent miiTor ; at each end of the board are panels in which the 
drawings are placed. The two|»eflected images coincide at the 
intersection of the optic axes, and form an image of the same 
apparent magnitude as each of the component pictures. This in- 
strument is called the reflecting stereoscope ; and as it will admit 
of being made of any size, so as to allow of the introduction of 
large pictm-es, it oSers many advantages. Mr. Wheatstone sug- 
gested in his memoir, already quoted, the use of an instrument 
constructed with prisms, which is analogous to the beautifully 
poi-table lenticular stereoscope of Sir David Brewster, described 
by him in the Philosophical Magazine. 

This instrument consists of two semi-len-ses, placed at such a 
distance that each eye views the picture or drawing opposite to 
it, through the margin of the semi-lens, or through parts of it 
equidistant from the margin. A lens, a a, being cut in two 

halves, these are fixed into a frame l and R, and adjusted to such 
distances that the centres of the semi-lenses correspond with the 
pupd of the eyes. The distance of the centre of one pupil from 
the other is at an average 2| inches, and to this the semi-lenses 
may be adjusted ; but if the instrument is provided with the 
means of effectiag a little change in this respect, it will often be 
found to be of considerable advantage. 



" When we thus view," says Sir David Brewster, " two dis- 
similar drawings of a solid object, as it is seen by each, eye 
separately, we are actually looking through two prisms, which 
produce a second image of each di-awing, and when these second 
images unite, or coalesce, we see the solid image which they 
represent. But in order that the two images may coalesce, 
without any effort or strain on the part of the eye, it is neces- 
sary that the distance of the similar pai-ts of the two drawings 
be equal to tivice the sepai'ation produced by the prism. For 
this piirpose measure the distance at which the semi-lenses give 
the most distinct view of the di-awings ; and having ascertained, 
by using one eye, the amount of the refraction produced at that 
distance, or the quantity by which the image of one of the 
drawings is displaced, place the drawings at a distance equal to 
twice that quantity; that is, place the drawings so that the 
average distance of similar parts in each is equal to twice that 
quantity. If this is not correctly done, the eye of the observer 
will correct the error by making the images coalesce "without 
being sensible that it is making any such effort. When the 
dissimilar drawings are thus united, the solid will appear stand- 
ing, as it were, in relief, between the two plane representations." 

The lenticular instrument, fitted for use, is shown in figure 85 ; 
it consists of a frame of wood or metal; the two semi-lenses are 
fixed in brass tubes, which are capable of being adjusted to ac- 



commodate tlie differences of sight in different individuals. At 
the bottom of the box, as seen through the opening, are placed 
the two stereoscopic pictui-es, which may consist either of dia- 
grams, similar to those already represented, or of images taken 
by the daguerreotype, talbotype, or coUodion processes. These 
photographic processes enable us to obtain such copies of exter- 
nal natiu-e as are i*equired to prodixce the magical results with 
which the stereoscope renders us familiar. It is required to take 
two pictures of a single object, at such a difference of angle as 
will produce the solidity which is evident in ordinary binocular 
vision, as the result of vie\\'ing two dissimilar images, under 
certain conditions, on a plane surface. 

The two accompanying figures represent a bust as viewed by 
each of the two eyes singly. If the experiment is tried upon a 

bust or statue, it will be found that one eye will see surfaces 
which are invisible to the other. Thus in these examples it 
will be quite apparent, upon examination, that the line of the 
cheek is more distant from the line of the nose in one than in 
the other image, and that a similar inequality exists in several 
other parts. By a little practice, any reader may, by squinting, 
resolve these two images into one, and thus produce the stereo- 
scopic effect. Now the object is to place the camera in the 
position of the eyes, and thus obtain the representation of two 
images, as viewed by each eye separately. This may be effected 
with a single camera, by adjusting it at a certain measured dis- 
tance from the object to be copied, and having obtained one 
picture, move it round about twenty degrees, and take the 





second image, a may represent the object to be copied, b being 
the distance at which the camera c is placed, which is, say 100 

i> feet from the point a ; 

the picture fi'om this 
\ point being taken, the 

"":-^\S^^ cameiTi is moved roxmd, 
'; still preserving the 
\ same distance from the 
object by means of a 
cord attached to the 
camera obsciu-a., or by 
/ measuring the space. 

5.' Two cameras with lenses 

^7 of the same focal length 

may be employed, and are indeed employed, by M. Claud et and 
others, for the piu-poses of obtaining stereoscopic portraits, and 
it is foxrnd that with lenses of the same focus, the figui-es are 
sufficiently exact for all practical purposes, and produce the 
most perfect stereoscopic pictiu-es. Sir Da^dd Brewster con- 
tends that it is not practicable to obtain sufficient exactness by 
either of these methods. He therefore proposes the use of a 
binocular camei^a, which he thus describes : — "In order to 
obtain photographic pictiu'es mathematically exact, we must 
construct a binocidar camera, which will take the pictures 
simidtaneously, and of the same size ; that is, a camera with 
two lenses of the same apertiu'e and focal length, placed at the 
same distance as the two eyes. As it is impossible to grind 
and polish two lenses, whether single or achromatic, of exactly 
the same focal lengths, even if we had the very same glass for 
each, I propose to bisect the lenses, and construct the instru- 
ment with semi-lenses, which will give us pictures of precisely 
the same size and definition. These lenses should be placed 
with theii" diameters of bisection parallel to one another, and at 
a distance of 2^ inches, which is the average distance of the 
eyes in man ; and when fixed in a box of sufficient size, will 
form a Ijinocular camera, which will give us, at the same instant, 
with the same lights and shadows, and of the same size, such 
dissimilar pictures of statues, buildings, landscapes, and living 
objects, as will reproduce them in relief in the stereoscope." 


If the nearest object be distant 50 feet, arrange the two 
cameras perfectly horizontally, and parallel to each other, plac- 
ing them 2 feet apart, measured from the centre of each lens. 


Let the distance between them (measured in this way), be 
always dii-ectly proportionate to the distance of the nearest 
object, which must be determined by the tape; thus, when the 
object is t^^^ice the above distance off (100 feet), place the cameras 
4 feet apart; for 150 feet, 6 feet apart, a'li.d so on. 

For trees it does not seem veiy important that perfect hori- 
zontal! ty of the cameras should be preserved. If they are 
aiTanged horizontally, it is only possible, in very peculiar situa- 
tions, to avoid making the foreground disagreeably and dispro- 
portionately large. 

IMi'. Fenton does not keep the cameras parallel in taking 
landscapes; but, observing Prof Wheatstone's inile, as above, 
respecting distances, inclines them so that the same object may 
occupy as nearly as possible the centre of each ground-glass plate. 

Extraordinary relief of distant objects may be obtained bj" 
arranging the cameras with special reference to them. Thus, 
views taken across the Thames, by placing the cameras 12 feet 
apart, produce an astonishing effect. In such -vT^ews, of course, 
no near objects must be admitted. 

Horizontal position of the cameras is absolutely necessary 
when buildings are taken; otherwise, when viewed in the ste- 
reoscope i-ilaced horizontally, they appear to be falling over. 

There appears but one objection to the binocular camera of 
Sii' David Brewster, and that is one arising from the circum- 
stance of employing really the veiy worst poi'tion of the lens ; 
i.e., the two sides. This, however, in practice is not foiind to 
be of any disadvantage ; the images are sufficiently perfect, 
although not so absolutely correct as those formed by the centre 
of the lens, and they are certain of being resolvable into a dis- 
tinct image of thi-ee dimensions. 

The following notes on the stereoscope were communicated by 
Professor Wheatstone to the Photographic Society : — 

" The most perfect and generally usefid form of the stereoscope 
is that with reflecting mirrors described in my earliest memou* 
' On Binocular Vision,' published in the Philosoj)hical Transac- 
tions for 1838. Pictiires of any size may be placed in it, at the 
proper point of sight, 'svith the proper convergence of the optic 
axeg, and it admits of every requ.isite adjustment to make the 
pair of binocular pictures coincide correctly. 

"I have described in my second memoir a portable stereoscope 
which folds into a small compass, and which is well suited for 
pictiu'es not exceeding six inches by foiu*. I have since con- 
structed an instrument, very convenient for caiTying about, 
which is adapted to exhibit joictures of the largest dimensions 
u.sually taken, as well as smaller ones, and which may be made 


use of either for mounted or unmounted pictm-es. When closed 
it occupies a space of 9 inclies in length, 5 in breadth, and 4^ in 
height j when expanded the instrument is 2 feet in length, 1 foot 
in height, and 9 inches in depth. The base and sides consist of 
jointed bars on the principle of the lazy-tongs ; the two miixors 
fold together back to back, and, by means of a hinge on their 
support, fall into a groove on the base fitted to receive them. 
On the top of each of the expanding sides a clip 9 inches in length 
receives the picture (which there is no need to mount on card- 
board), and holds it by the pressm-e of a suitably disposed sj^riug ; 
and a similar but detached spring clip is applied to the lower end 
of the picture, in order to keep it flat and in a vertical position. 

"The pictures being fixed in the clips, so that theii- reflected 
images shall appear single and coincide in all theii' parts, the 
accui'ate adjustment to the sight of diflferent persons is efifected 
by sliding to and fro the pillar which supports the min-ors; the 
optic axes being caused to converge more as the mirrors are 
moved towai'ds the eyes, and vice versa. As the height of the 
sides is variable through every degree, the pictures are easily 
adjusted to the same level by pressing on the side which is 
highest. The length of the base being also variable, the pic- 
tui-es, if it be required, may be placed at different equal distances 
from the min-ors. If the pictures are not straight with respect 
to the sheets of paper on which they are placed, one end may 
be brought lower than the other merely by di-awing down that 
end so that it shall not enter the clip so far as the other. 

" The instiixment is furnished ^^dth a pair of ordinary spectacle 
lenses, No. 24. If the pictures were so placed that their reflected 
images coincided when the optic axes made an angle of IS'', 
corresponding to the distance of 12 inches, no lenses would be 
requisite, as the distance of the binocular image, the conver- 
gence of the optic axes, and the adaj^tation of the eyes to distinct 
vision, woidd have their cvistomary con-espondence. But, for 
reasons I have elsewhere stated, a much better effect is produced, 
and the objects appear larger and more distant, when the pictiires 
are so placed that, to cause their* most distant corresponding 
points to coincide, the optic axes are parallel, or nearly so ; in 
this case, however, in order to see the objects distinctly, the 
rays proceeding from them must be rendered less convergent, 
and for this purpose lenses are necessary. 

"The lenses are movable in a vertical dii-ection, in order that 
they may be fixed at the proper point of sight ; the effect of a 
stereoscopic pictiu-e gi-eatly depends on its being thus viewed, 
though it is a circumstance which is very generally disregarded." 

With the single camera, taking the precaution named, with 


two lenses of the same focal length, or with the semi-lenses, 
stereoscopic pictures may be obtained without difficulty. 

The magic result of the resolution of two plain pictures 
into one, possessing to the eye the most positive solidity, is so 
striking when witnessed for the first time, that it appears to be 
a deception of the senses. Even when fully accustomed to the 
phenomena of the stereoscope, there is an indescribable charm 
in the beautiful pictiu-es, that they are gazed at again and again 
with increasing admiration. Living forms appear to stand out 
in all the roundness of life ; and where colours have been judi- 
ciously applied to the daguerreotype or calotype portrait, it is 
not possible to conceive a more perfect realization of the human 
form than that which stands forth, prominently, from the back 
ground of the stereoscopic picture. Statues, in like manner, are 
almost realized again in their miniatm*e representations. Archi- 
tectural piles are seen in all that exactness of proportion and 
gradation of distance, which is, in their minute reproduction, 
singularly interesting ; and in landscapes, the stereoscope gives 
us a reformation of every image in apparently the most perfect 
solidity and truth of distance. In the stereoscope we have at 
once an instrument which enables us to study many of the 
phenomena of vision, and to reproduce loved and beautiful 
objects, or interesting scenes, tlu-ough the agency of those rays 
by which they were illuminated, in that strange perfection which, 
in its mimicry of visible external natiu'e, almost baffles the 
examination of hrmian sense. 


Photographic Exgraveng. 

^Ir. Fox Talbot has, since the publication of the former edi- 
tion of this treatise, published some accoxmt of his experiment 
to etch on steel the impression produced by the solar rays. He 
thus describes his process : — 

" The first thing to be done is to select a good steel plate, and 
to immerse it for a mini;te or two in a vessel containing vinegar, 
mixed -ttith a little .svdjjhuric acid. The object of this is to di- 
minish the too great polish of the surface ; for other^vise, the 
photographic preparation ■would not adhere "well to the surface 
of the steel, but would peel off. The plate is then to be "well 
"washed and dried. Then, take some isinglass and dissolve it in 
hot "water. The solution should be strong enough to coagidate, 
"when cold, into a fii-m jellv. This solution of isinglass or gelatine 
should be strained "while hot through a linen cloth to piuify it. 
To this must be added about half as much of a satiu^ted solution 
of bichi'omate of potash in "water, and they should be "well stirred 
together. When cold, this mixtiu-e coagidates into a jelly, 
"which has veiy much the appearance of orange jelly. The me- 
thod of using it is to liquefy it by gentle heat, and to pour a 
quantity upon the centre of the steel plate. Then take a glass 
rod, hold it horizontally, and spread the liquid uniformly over 
the plate. Then incline the plate, and poiu' off the superfluous 
gelatine. Let the steel plate be placed upon a stand, and kept quite 
horizontal, that the liquid may not run to one side of the plate. 
Then place a spiiit lamp beneath the plate, and "warm it gently 
tiU the gelatine is quite di-ied up. When dry, the film of gela- 
tine ought to be bright yeUo"w and very uniform. If clouded 
bands appear upon the siu-face, it is a sign that there is too Little 
gelatine in proportion to the bichromate, which must therefore 
be corrected. The steel plate now coated "v\-ith gelatine, is ready 
to receive a photographic image of any object. First, let us sup- 
pose the object is one capable of being applied closely to the sur- 
face of the plate ; for instance, let it be a piece of black lace or 
the leaf of a plant. Place the object upon the plate in a photo- 
graphic copying-frame, and screw them into close contact. Place 


this frame in the direct light of the sun for a short time, vary- 
ing from half a minute to five minutes. Let it then be removed 
and the plate taken out, and it will be fovmd impressed with a 
yellow image of the object upon a ground of a brown coloui-, as 
might be expected from the well-known photographic property 
of the bichromate. The plate is then to be placed in a vessel of 
cold water for a minute or two, which dissolves out all the bi- 
chromate and most of the gelatine also from the photographic 
image, i. e., from those parts of the plate which have not been 
exposed to the smi, being protected by the object ; while, on the 
contrary, it dissolves little or none of the gelatine film which 
has been fnlly exposed to the sun's rays. The consequence of 
which is, that instead of a yellow image, we have now a white 
one, but still upon a ground of bro^mi. The plate is then re- 
moved from the water into a vessel of alcohol for a minute, and 
it is then taken out and placed upright on its edge in a warm 
place, where in the course of a few minutes it becomes entirely 
dried. Tliis terminates the photographic part of the operation. 
If the plate is carefully examined while in this state, it appears 
coated with gelatine of a yellowish brown coloiu", and impressed 
with a white photogra^iliic image, which is often eminently 
beautiful, owing to the circumstance of its being raised above 
the level of the plate by the action of the water. Thus, for in- 
stance, the image of a piece of black lace looks like a real piece 
of very delicate white lace of similar pattern, closely adheiing to, 
but plainly raised above, the brown and polished surface of the 
plate, which serves to display it veiy beautifully. At other 
times the white image of an object offers a varying display of 
light when examined by the light of a single candle, which indi- 
cates a peculiar molecular arrangement in the particles of gela- 
tine. These photographic images are often so beautiful that the 
operator feels almost reluctant to destroy them by continuing 
the process for engraving the plate. 

" In order to explain how such an engi-aving is possible, it is, 
in the first place, to be observed that the photographic image 
differs from the rest of the plate, not only in coloiu', but, what 
is of much more importance, in the thickness of the film of gela- 
tine which covers it. The coating of gelatine on the rest of the 
plate is, comparatively sj)eaking, a thick one, but that which 
originally covered the image has beenmostly removed by the action 
of the water, a small portion, however, almost always remaining. 
It therefore naturally happens that when an etching liquid is 
poured on to the plate, it first penetrates through the thin gela- 
tine covering the image, and etches the steel plate beneath. 
But the next moment it penetrates likewise through the thicker 


coating of gelatine, and thus spoils the resiJt by etching the 
"whole of the plate. Nitric acid, for instance, does this, and 
therefore cannot be employed for the purpose. Since the other 
chemical liquids wliich are capable of etching steel have a certain 
analogy to nitric acid in their corrosive jiroperties, they also for 
the most jDart are found to fail in the same manner. 

"This was a difficvilty. But after some researches I found a 
liquid which etches steel perfectly well, and at the same time is 
fi*ee from the inconvenient property of jjenetrating the gelatine 
film. This liquid is the bichloride of platinum. In order, how- 
ever, to use it successfully, it must be mixed -with a cei-tain 
quantity of water, neither more nor less (I mean, to any material 
extent), otherwise its action becomes irregular. The best way 
is to make a perfectly saturated solution, and then to add to it 
one-foiu-th of its bxilk of water. Then correcting this by a few 
trials, a solution of proper strength is finally obtained. Sup- 
posing, then, that we have prepared such a solution, the opera- 
tion of etching the plate is performed as follows : — The plate is 
laid on a table, and a small quantity of the bichloride being 
poiu'ed upon it, it is to be rapidly difiiised and spread over the 
whole plate with a camel-hair brush. Not much liquid is poured 
on, because its opacity would prevent the operator from distin- 
giiishing the efiect produced by it on the metal. For this reason, 
it is hardly necessary to make a wall of wax round the plate ; that 
is, if the portions to be etched are confined to the central jjart of 
the plate, and do not approach very near to the edge. The 
efiect of the liquid upon the plate is not at first visible, since it 
disengages no gas ; but after the lapse of a minvite or two, the 
white photographic image begins to darken, and soon becomes 
black in every part. "When this change is complete, the image 
often looks veiy beautiful, though quite altered from what it 
was before. The operator should carefully watch the image until 
he thinks that it is finished, or not likely to be fiu'ther improved 
or developed by continixing the process any longer. He then 
inclines the plate gently, and pom-s ofi" the liquid by one corner 
of the plate. The plate is then dried with blotting-paper, and 
then a stream of salt water, which is better than fi-esh water for 
this purpose, is poured over the plate, which removes all traces 
of the etching liquid. The plate is then nibbed with a wet 
sponge or linen cloth, which in a short time detaches and re- 
moves the film of gelatine, and discloses the etching that has 
been effected. When the object is not of a nature to be applied 
directly to the surface of the plate, the most obvious method of 
proceeding is, of course, to place the prepared plate in the focus 
of a camera, and to direct the camera to the object. But in 


consequence of the low degree of sensitiveness of bichromate of 
potash, this would take, generally speaking, too long a time to 
accomplish. The better way in practice, therefore, is to take a 
negative photograph of the object on paper with a camera, and 
from this to obtain a positive copy either on glass or paper, 
which should be very uniform in texture, and moderately trans- 
parent. Then this positive copy is placed on the plate in a pho- 
tographic copying-frame, and being placed for a few minutes in 
the sun, it impresses the plate with a photograpliic image ; which 
image, etched as above described, and printed off upon paper, 
will finally give a positive representation of the object. If the 
object depicted upon the plate by the sun's I'ays is broad and 
uniform, for instance, the opaque leaf of a plant, then, of course, 
the etching is uniform also. When this is printed off, it pro- 
duces an effect which is not always satisfactory. I will there- 
fore now explain a moflification of the process which destroys 
this uniformity, and which in many cases produces a great im- 
provement in the general effect. 

" For this pui'pose I must remai-k, in the first place, that if a 
piece of black gauze or crape is the object selected for represen- 
tation, it produces an engraving of itself Avhich is marvellously 
accurate. But when two folds of the gauze are laid across each 
other obliquely, then the resulting engraving requires a lens in 
order to separate from each other and distinguish clearly the 
lines belonging to the two portions of the gauze. Now, if this 
engraving is printed off, the result offers to an eye at a moderate 
distance the appearance of a uniform shading. Now, I avail 
myself of this circumstance to modify my original process as fol- 
lows : — suppose the object to be the opaque leaf of a plant, of 
irregular outline, first, I cover the prepared plate with two ob- 
lique folds of black crape or gauze, and place it in the sunshine 
for two or three minutes. The effect of this is to cover the plate 
with a complicated image of lines passing in all directions. Then 
the leaf is substituted for the crape, and the plate is replaced in 
the sunshine for two or three minutes more. The leaf being 
then removed from the plate, it will be seen that the sun has obli- 
terated all the lines that were visible on the parts of the plate 
exterior to the leaf, converting all those parts to a uniform 
brown. But the image of the leaf itself is still covered -with a 
network of innumei-able lines. Now, let this be etched in the 
way already described, and let the resxilting etching be printed 
off. The result is an engraving of the leaf, which, when beheld 
by the eye at a certain distance, appears uniformly shaded, biit 
when examined closely, is found to be covered with lines very 
much resembling those produced by an engraver's tool, so much 


SO tliat even a practical engraver woT;ild probably be deceived by 
the apjDearance. This crape ari'angement I call a photograjjMc 
veil ; and as I think it likely that the idea ^411 prove useful, I 
will make a few more remarks upon it. It is cleai' that an 
arrangement composed of two thicknesses of ordinary crape or 
gauze is but a nide attempt at a photogi-aphic veil. To realize 
the practical utility that may result from the idea, supposing it 
to be bonie out by fui-ther experience, it would be pi'oper to 
fabricate a much finer material, and to employ five or six thick- 
nesses of it, or else to cover a sheet of glass in any convenient 
manner with an innumerable quantity of fine Hnes, or else with 
dots and specks, which must be opaque and distinct from each 
other. The result of practically emjDloying such a method, sup- 
posing always that it answers in practice, as I think it probably 
•will, would be an etching apparently uniform, but really con- 
sisting of separate small portions, in consequence of which it 
would hold the ink much better, and other obvious advantages 
would also be obtained. Another mode of accompKshing the 
same object is to cover the plate originally M-ith an aqua -tint 
groirud. But then a fresh one would be requii-ed for every plate, 
whereas a single veil would serve for any nimiber of plates in 
succession. Experience alone can decide between these difierent 
methods. "When the etching is finished, the plate should be 
very soon coated with wax to protect it. A few houi's' exjDosure 
to the atmospheric air nxsts and destroys the etchings when 
newly made, although it does not do so afterwards. The oxida- 
tion only attacks the lines of the etching, the rest of the jilate 
sustaining no injiuy, if the air is tolerably diy." 

By the process of M. Niepce {Heliograjyhy) described in the 
historical sections, some etchings on metal plates were obtained. 
Recently his nejihew, M. Kiepce de St. Victor, has been retui-n- 
ing to this process with some success — ^being assisted in the 
etching process by M. Lemaitre. These gentlemen have thus 
described their process : — 

"The steel to be operated on having been freed from grease by 
whitening, M. Lemaitre pours upon the polished siu-face water 
acidulated with hydrochloric acid, in the proportions of 1 part of 
acid to 20 parts of water : this is what he does in aquaforiis en- 
gi-aving before applying the varnish ; by this means the varnish is 
made to adhere perfectly to the metal. The plate must then be 
well washed A^dth piu-e water and diied. Kext, by means of a 
roll of cloth covered with leather, he spreads upon the polished 
surface the bitumen of Jud?ea dissolved in essential oil of lavender, 
submits the vami-sh thus applied to a moderate heat, and when 
dry, preserves the j^late from the action of light or damp. 


" On a plate thus prepared, I apply the face of a dii-ect (or posi- 
tive) photogi-aphic proof upon albiuninized glass or waxed paper, 
and expose it to the light diu'iug a length of time, varying ac- 
cording to the nature of the proof to be reproduced, and the in- 
tensity of the light ; in any case the operation is never very 
long ; for a proof may be obtained in a quarter of an hour in the 
sun, and in one hoiu' in diffuse dayhght. Indeed it Ls necessary 
to avoid prolonging the exposui'e too much, for in such case 
the image becomes visible before the operation of the solvent, 
which is a signi that the jiroof is a failm-e, because the solvent 
will no longer produce any effect. 

"I use, as solvent, 3 parts of rectified oil of naphtha and 1 part 
of benzine (prepared by Colas). These proportions have usually 
given me good results ; but they may be varied, in proportion 
to the thickness of the layer of varnish and the time of exposure 
to light, for the moi'e benzine there is the more solvent the 
action. The essential oils produce the same effect as benzine, 
that is to say, they remove the portions of varnish which have 
been preserved from the action of light. I have disco veiled that 
ether acts in the opposite way. 

" In order quickly to arrest the action and remove the solvent, 
I throw water upon the plate so as to form a sheet, and I thus 
remove the whole of the solvent. I then dry the drops of water 
which remain upon the plate, and the heliograpliic operations 
are terminated. 

" It now remains to speak of the operations of the engraver. 
M. Lemaitre has undertaken to describe them. 

" Note of M. Lemaitre. 

" Composition of the mordant or biting liquid : 

Nitric acid 36° 1 part (by volume). 

Distilled water 36'' 8 „ „ 

Alcohol 36^ 2 „ 

" The action of the nitric acid, diluted with water and alcoholized 
in these proportions, commences immediately the mordant is 
poured upon the steel plate, prepared in the manner just de- 
scribed, while the same quantities of nitric acid and water, with- 
out alcohol, have the inconvenience of remaining inert for at 
least two minutes after contact ; I leave the strong mordant only 
a very short time upon the plate, I remove it, wash and well 
dry the varnish and the engraving, so as to be able to continue 
and bite more deeply into the metal without injuring the helio- 
graphic laj^er. For that purpose I use resin reduced to very 
fine powder ; placed at the bottom of a box prepared for this 


piirpose, I agitate it by means of a pair of bellows, so as to form 
a sort of cloud of dust which is allowed to settle upon the plate, 
as is the practice in aqua-tint engraving. The plate is then 
heated ; the resin forms a network all over the engraving, and 
it consolidates the varnish, wliich is then capable of resisting for 
a long time the corrosive action of the mordant (nitric acid 
diluted with water, without addition of alcohol). It forms on 
the blacks a fine grain, which receives the printing ink, and 
enables us to obtain good and numerous impressions after the 
varnish and the resin have been removed by the aid of heated 
greasy substances and essential oils. 

"The residt of all these operations is, that, without the help of 
the bui"in, we may reproduce and engrave on steel all photogi-aphic 
impressions on glass or paper, and without employing the camera 

Processes analogous to these have been employed to obtain 
impressions upon lithogi'aphic stones, which, having been treated 
in the usual manner, are rendered capable of producing any 
number of impressions. 


The following coiTespondence, important in the histoiy of pLo- 
tography, appeared in the Times newspaper of AugustlS, 1852 : — 


We have been requested to publish the following corre- 
spondence between the Presidents of the Royal Society and the 
Royal Academy, and the patentee of the ai-t of photogTaphy upon 
paper, with the \dew of definitively settling a question of con- 
siderable interest to aitists and amateiu-s of photography in 
general : — 

No. 1. 

London, July, 1852. 

Dear Sir, — In addressing to you this letter, we believe that 
we speak the sentiments of many persons eminent for their love 
of science and art. 

The art of photogi'aphy upon paper, of which you are the 

[ inventoi', has arrived at such a degree of perfection that it 

i must soon become of national importance ; and we are anxious 

I that, as the art itself originated in England, it should also 

receive its further perfection and development in this coimtry. 

At present, however, although England continues to take the 

lead in some branches of the art, yet in othei-s the French are 

unquestionably making more rapid progress than we are. 



It is very desii-able tliat we slioxild not be left behind by the 
nations of the Continent in the improvement and development 
of a piu'ely British invention ; and as yon are the possessor of 
a patent right in this invention, which will continxie for some 
years, and which may, perhaps, be renewed, we beg to call yonr 
attention to the subject, and to inquu-e whether it may not be 
possible for you, by making some alteration in the exercise 
of yoiu' patent rights, to obviate most of the difficulties which 
now appear to hinder the f)rogress of the art in England. Many 
of the finest applications of the invention will, probably, require 
the co-operation of men of science and skilfid artists. But it is 
evident that the more freely they can use the resoiu'ces of the 
art, the more probable it is that their efforts will be attended 
with eminent success. 

As we feel no doubt that some such judicious alteration would 
give great satisfaction, and be the means of rapidly improving 
this beautifid art, we beg to make this friendly communication 
to you, in the full confidence that you will receive it in the same 
spirit — the improvement of art and science being oiu- common 



To H. F. Talbot, Esq., F.R.S., &c., 
Lacock Abbey, Wilts. 

No. 2. 

Lacock Abbey, July 30. 

My Deae Lord Rosse, — I have had the honour of receiving 
a letter from yourself and Sir C. Eastlake respecting my 
photographic invention, to which I have now the pleasure of 
replying. ^ 

Ever since the Great Exhibition, I ha^'c felt that a new era 
has commenced for photography, as it has for so many other 
usefiil arts and inventions. Thousands of persons have now 
become acquainted with the art, and, from having seen such 
beautiful specimens of it produced both in England and France, 
have natm-ally felt a wish to practise it themselves. A variety 
of new applications of it have been imagined, and doubtless 
many more remain to be discovered. 


I am unable myself to piirsiie all these niimerons branches of 
the invention in a manner that can even attempt to do justice 
to them, and moreover, I believe it to be no longer necessaiy, 
for the art has now taken a firm root both in England and 
France, and may safely be left to take its natural development. 
I am as desirous as any one of the lovei-s of science and art, 
whose wishes you have kindly undei'taken to represent, that our 
country shoidd contiaue to take the lead in'this newly-discovered 
branch of the fine arts ; and, after much consideration, I think 
that the best thing I can do, and the most likely to stimulate to 
fiu'ther improvements iv photography, will be to invite the 
emulation and competition of oiu- artists and amateurs, by re- 
laxing the patent right which I possess in this invention. I 
therefore beg to reply to your kind letter by offering the patent 
(with the exception of the single point hereafter mentioned), as 
a ti'ee present to the public, together with my other patents for 
improvements in the same art, one of which has been very 
recently gi-anted to me, and has still thirteen years unexpired. 
The exception to which I refer, and which I am desii'ous of still 
keeping in the hands of my own licensees, is the application of 
the invention to taking photographic portraits for sale to the 
public. This is a branch of the art which must necessarily be 
in comparatively few hands, because it requii-es a house to be 
built or altered on purpose, having an apartment lighted by a 
skylight, &c., otherwise the portraits cannot be taken indoors, 
generally speaking, without great difficulty. 

With this exception, then, I present my invention to the 
covmtry, and trust that it may realize our hopes of its future 

Beheve me to remain, my dear Lord Eosse, 

Your obliged and faithful servant, 


The Earl of Eosse, Connaught Place, London. 




English Weights. 

English Grains. French Grammes. 

2-6803 — Troy . 

- 15438- 

1000- = 1 Kilogramme 

1 Pound Avoirdupois 



1 _ Troy . 



] Ounce Troy 

480- • 


1 — Avoirdupois 



1 Drachm Apothecaries 



1 — Avoirdupois 



1 Imperial grain . 




1- =1 Gramme 


0-1 = 1 Decigramme 


0-01 = 1 Centigramme 


0-001= 1 Milligramme 

English Imperial Meji 


French LrrRES. 

1 Gallon . 

. 4-5455 

1 Pint = 20 fluid ounces 

. 0-5682 

1 Decigallon =16 fluid ounces . . 0'4545 

Fluid ounce, being the bulk of an 
avoirdupois ounce of VFater at 62° 

Fluid drachm 

Septem, being the bulk of 7 grains of 


water at 62° Fahr. or the THKnn of 

a gallon 
0-22 Gallon 
1-76 Pint . 
2-20 Decigallon . 
2-2 Septems 
15-4 Grains of water at 62° Fahi-. 





1 Centimetre Cube 


Acetate of lead, photographic use of, 

Achromaticity, 168. 
Actinic focus, 137. 
Actinism, term proposed. 111. 
Albumen in Talbot's instantaneous 

process, 31. 
Albumen processes, 95. 

on paper, 223. 

on glass plates, 276. 

Alcohol extracts, colooring matter of 

flowers, 62. 
Alkahes, stimulating effects of, 67. 
Ammonia-citrate of iron, 53. 
Animoriia-nitrate of silver, 193. 
Amphitype, the term, 33. 

of Sir J. Herschel, 59. 

Apparatus required, 183. 
Appendix, 391. 
Arago on chemical rays, 142. 
Archer on the collodion process, 252. 

on whiting coUodion image, 265. 

Archer's collodion camera, 268. 
Asphaltum used in hehography, 12. 

Bayard on positive photographs, 295. 

Becquerel modifies Ponton's process, 71 . 

on rays of spectrum, 133. 

Becquerel's coloured photographs, 160. 

Berard on magnetizing power of violet 
ray, 5. 

on chemical spectrum, 9. 

Berres on fixing daguerreotypes, 247. 

Berzelius on peculiar conditions of 
salts of gold, 9. 

on precipitates of gold, 55. 

Bingham on chromatype, 72. 

on calotype process, 212. 

Binocular vision, Wheatstone on, 305. 

Biot, M., on the calotype, 21. 

Bitumen of Judea used by Xiepce, 12. 

Bleaching power of iodine salts, 285. 

Bockman, action of light on phospho- 
rus, observes, 6. 

Botanical specimens, to arrange, 185 
Brewster on the spectrum, 108. 

on the stereoscope, 308. 

Bromide of sUver and mercurial vapour, 

of silver, 118. 

of potassium, use of, 119. 

of iodine, to prepare, 238. 

Bromine box, 238. 
Bromidized collodion, 273. 
Brook's photographic registration, 140. 
Buffing daguerreotype plates, 235. 
Buildings, &c., to copy, 298. 

Calotype, the, 20. 

improvements in the, 27. 

modern improvements in, 


process on gelatine and albu- 
men, 222. 

on wax-paper, 227. 

Camera obscura for daguerreotype, 39. 

varieties of, 186. 

folding, 191. 

for coUodion, 267. 

general remarks on, 


Catalysotype, the, 75. 

Change on silver salts examined, 116. 

Channing modifies calotype, 213. 

Charles, M., said to have produced 
photographs, 5. 

Chemical spectrum, 110. 

China clay used in paper, 180. 

Chlonde of sUver observed to blacken, 4. 

of silver, 115. 

of silver, to form, 194. 

Chlorine, combination with hydro- 
gen, 9. 

Chromatic aberration, 167. 

Chromatype, the, 71. 

Chrysotype, the, 54. 

Claudet and Goddard improve the 
daguerreotype, 99, 



// Claudel on the daguerreotype, 132. 

.'-^ 's mercurial chamber, 243. 

Collodion process, 252. 

to prepare, 254. 

process, to iodize, 254. 

introduced in photography, 


Colours destroyed by comjilementary 

ray, 65. 
■ of positive photographs by one 

process, 84. 

■ , question of producing them 

natui'ally, 158. 

, actinic, explained, 171. 

of plate when sensitive, 237. 

Complementary rays destroy cohnirs 65. 

Cooper's method of washing paper, 195. 

Copper, plated, used by Niepce, 14. 

Corchorus japonica, colouring matter 
of, 64. 

Corrosive sublimate, action of on pho- 
tographs, 87. 

Cotton, gun, for collodion, 252. 

Crookes on the use of bromine, 273. 

Cundell on the calotype, 206. 

Cj'anotype, the, 48. 

Daguerre on Niepce's process, 15. 

, history of his discovery, 34. 

■ observes variations in photo- 
graphic action, 113. 
• improves iodizing 


Daguerreotype, the, 34. 

, improvements in, 43. 

applied to paper, 85. 

— , theory of the, 124. 

■ , the improved, 230. 

• simplified, 248. 

Davy, Sir H., on change in puce-co- 
loured oxide of lead, 5 . 

• , Sir H., on Wedgwood's experi- 
ments, 7. 

, Dr., on change in solution of 

coiTOsive sublimate, 8. 

Delamotte on developing collodion 
image, 259. 

Desmortiers on discoloration of Prus- 
sian blue, 6. 

Developing calotype picture, 209. 

. daguerrean image, 243. 

Diactinic lens explained, 171. 

Diamond, Dr., his practice on collo- 
dion, 264. 

Dippel, animal oil of, used by Niepce, 15. 

Discoloration of papers, 179. 

Double salts of iron in cyanotype, 53. 

Draper, Dr., on daguerreotype pro- 
traits, 96. 

— -, Dr., on radiant images, 152. 

Draper's experiments with chlorine, 9. 

experiments on solar spec- 
trum, 113. 

Dynactinometer, the, described, 146. 

Eggs, white of, photographic use, 225. 

Energiatype original of ferrotype, 73. 

Englefield, Sir H., on heating power 
of solar rays, 5. 

»- on phosphorescence, 9. 

Engravi\ig by M. Niepce's process, 14. 

■ , photographic, 314. 

Everard Blanquart's calotype, 213. 

BlanqPh't's albuminized pa- 
per, 226. ,,.. M 

Exciting collodjoai^late, 256. 

Experiments on salts of silver, 115. 

on iodide of silver, 292. 

Exposure in the camera of calotype 
paper, 209. 

Ferro-tartrate of silver, 58. 
FeiTocyanide of potassumi, photo- 
graphic use of, 79. 
Ferrotype, the, 73. 
Fixing the daguerreotyj^e picture, 43. 
■ the photographic picture, 198. 

the calotj-pe picture, 210. 

collodion image, 261. 

Fizeau's bromine water, 237. 
Fizeau fixes with chloride of gold, 245. 
Flacheron's caloty]3e process, 215. 
Flowers, colouring matter of, 61. 
Fluoride of silver, 120. 
FluorotyiDe, the, 80. 

Focimeter, the, described, 145. 
Focus of lenses for photography, 137 
Forces, antagonistic, in sunbeam, 112. 
Fresnel on chemical action of rays, 142. 
Fry on the collodion process, 252. 
Fulminate of silver, 121. 
Fyfe, Dr., on phosphate of silver, 121. 

Gallo-nitrate of silver in calotype, 208. 

Gaudin, M., on daguerreotype, 134. 

Gay-Lussac and Thenard's investiga- 
tions of chlorine, 9. 

Gelatine on paper, 222. 

Glass plates, cleaning of, 255. 

, albuminized, 276. 

Goddard, Wm., first introduces use of 
bromine, 47. 


Goddard on bromide of iodine, 239. 
Gold and silver, difference between, 

according to the alchemists, 4. 

, employed in chrj'sotype, 55. 

, salts of, used as photographic 

agents, 89. 
Gray, Le, on fixing photographs, 202. 

, processes on glass, 276. 

, |albumen process on paper, 

Green glass, use of. 109. 
Griffin's modification of Archer's 

camera, 269. 

Harrup refutes Eumford's experi- 
ments, 5. 

Havell's etchings on glass, 284. 

Heat and chemical action considered, 

Heating powers of the prismatic rays, 

Heliochromes of Niepce, 161. 

Heliograph of Mr. Jordan, 141. 

Heliography discovered by Niepce, 11. 

, the process so called, 12. 

Herschel on fixing photographs, 205. 

, Sir W., on heating power 

of solar rays, 5. 

, Sir J., on the prismatic rays, 


on the photographic camera, 


on bromide of silver, 221. 

Herschel's photogi-ajAic processes, 48. 

chrysotype, 54. 

History of the discoveries in photogra- 
phy, 3. 

of photography, general sum- 
mary, 100. 

Horn, silver observed to blacken, 4. 

Home, Mr., on collodion, 255. 

Hungarian liquid, 237. 

Hyalot;y-pes, 283. 

Hydriodic acid, its bleaching power, 

Hydrogen and chlorine, 9. 

Hyposulphite of soda used in washing, 

of soda, 201. 

Indices of refraction for chromatic 

rays, 167. 
Instantaneous process of Talbot, 31. 
Instrument, meteorological, registered 

by photography, 139. 

Instruments used in daguerreotype, 

Iodide of iron used by Talbot, 32. 

of silver, 118. 

of silver, to form, 197. 

of silver, reasons for rejecting 

it, 221. 

Iodides, various bleaching powers of, 

Iodized gelatine paper, 223. 
Iodizing daguerreotype plate, 37. 

collodion, 254. 

Iron, iodide of, used by Dr. Woods, 32. 

- sulphate, used by Robert Hunt 

- , ammonia citrate of, 53. 

- , protosulphate of, photographic 
use of, 75. 

- , syrup of iodide of, used by Dr. 
Woods, 76. 

- salts used in collodion, 265. 

Jordan, Mr., first registers instruments 
by photography, 139. 

on iodizing paj)er, 213. 

Jugglers of India, statement respect- 
ing, 4. 

Knight's dynactinometer, 149. 

Laborde on bromodized coUodion, 273. 
Landscapes, peculiarity of, on Niepce's 

plates, 14. 
Langenheim's pictures on glass, 283. 
Lassaigneon positive photographs, 295. 
Latent light, Moser on, 151. 
Lavender, oil of, used by Daguerre, 15. 
Lemaitre on engraving, 319. 
Lenses, on, 163. 

, forms of, 165. 

Lenticular stereoscope, 308. 

Light and chemical action considered, 

, refraction of, 163. 

Lithographic impressions by photo- 
graphy, 319. 

Lxmiinous power of the solar raj's, 109. 

Magnetic power of violet ray, 5. 
JNIaloue's pictures on porcelain ta- 
blets, 29. 

albumen process, 278. 

Martin, Adolphe, on collodion process, 

Martin's calotype process, 214. 
— process on glass plates, 281. 



Materials, fixing, employed, 200. 
Media, coloured, employed by MeUoni, 

Melloni on separating light and heat, 

Mercurial vapour and bromide of 

silver, 81. 

chamber, 243. 

Mercury applied to daguerreotype, 41. 

, photographic properties of, 


Metals impressed with juxtaposed 
images, 153. 

Miscellaneous processes, 69. 

Moigno Abbe on M. Charles' pro- 
cess, 5. 

Montizon, Coimt de, on the collodion 
process, 258. 

Morichini on magnetism induced by 
solar rays, 5. 

Moser, M., on the formation of the 
daguerrean images, 151. 

Muller's calotype process, 217. 

Negative photographs, 183. 

wax-paper, to prepare, 229. 

Newton, Isaac, Sir, on the spectrum, 


Niepce and Daguerre, 34. 

, de St. Victor, applies albumen, 


, de St. Victor's, coloured photo- 
graphs 160. 

Niepce 's process of engraving, 818. 

production of pictures by 

light, 10. 

Nitrate ofsilver, to spread on paper, 193. 

ofsilver, 114. 

Nomenclature, new, proposed, 171. 

Operations of preparing dagueiTeotype 

plate, 35. 
Organic salts of silver, 122. 

Papaver rheum, colouring matter of, 63. 

orientale, 65. 

Paper, Ilerschel's experiments on, 177. 

, photogenic, of Fox Talbot, 19. 

, qualities of, 176. 

, selection of, 175. 

■ — — , calotype, 206. 
Pentagraph, photographic, 302. 
Petit, iafluence of hght on crystal- 
lization, 4. 

Philosopher's stone, 4. 
Phosphate of silver, 120. 

Photogenic drawings, 18. 
Photographic lens, conditions of a, 166. 
processes of Herschel, 



properties of mercury, 
, peculiarities of paper. 

Photographometer of Claudet, 136. 

, the, described, 143. 

Photographs, positive, by one process, 


on glass plates, 92. 

in natural colours, 159. 

— , positive, by iodine, 285. 

Photography, practice of, 157. 
Pictures on porcelain tablets, 28. 
Plate, daguerreotj'pe, to polish, 235. 

, to give sensitive surfaceto, 241. 

Ponton's, Mr., process, 69. 
Poppy, red, 68. 

Porcelain tablets, pictures on, 28. 
Portraits from the life, to take, 300. 
Portraiture by daguerreotype, 96. 
Positive photographs from etchings, 

photographs by one operation, 


photographs, 183. 

Potash, bichromate of, 69. 
Potassium, ferroeyanide of, as a fixing 
agent, 200. 

, bromide of, as a fixing agent, 

Preparation of gun cotton, 252, 
Preschot on fixing daguerreotypes, 246. 
Pressure frames, 185. 
Processes modified, 282. 
Process of daguerreotype, 34. 
Proto-nitrate of mercury used, 57. 
Prussiate of potash, formation of in 
cyanotype, 51. 

Rays, exciting, 133. 

• , continuating, 133. 

, passage of, through lenses, 165. 

Reflecting camera obscura, 99. 

steresocope, 307. 

Refractive powers, 164. 
Registration, photographic, 139. 
Regnault's calotype process, 219. 
Reproduction of pictures, spontaneous, 

Researches, early, on the chemical 

action of the solar rays, 3. 
Ritteron the invisible chemical rays, 5. 



Ronald's pliotographic registration, 

Eoss and Thomson's albumen pictnres, 

Rides for stereoscopic landscapes, 310. 

Eumford, Count, on the chemical pro- 
perties attributed to light, 4. 

Sage, M. B. G., on change in realgar, 8. 
Salt as a fixing agent, 200. 
Schafhaeutl on positive photographs, 

Scheele's researches on light, 4. 
Seebeck experiments on chlorine, 9. 

produces colour on chloride 

of silver, 9. 

Seguier on iodizing, 242. 

Senebier on chemical action of violet 

ray, 4. 
Senicio splendens, colouring matter of, 


photographic use of 

juice, 6S. 

Sensibility of daguerreotvpe plate, 

Sensitive papers, to prepare, 193. 

coating, to give to a plate, 236. 

dagueiTeotype mixtures, 236. 

Shaw, Mr. G., on daguerreotv'pe, 125. 
Silver salts on glass plates, 92. 

, bromide of, 118. 

• ■ , iodide of, 118. 

Silver-nitrate, 193 ; Ammonia, nitrate, 

194 ; Chloride, 194 ; Iodide, 197. 

Smee on ferrosesquicyanuret of potas- 
sium, 49. 

Soda, hyposulphite, 201. 

Solar agency producing chemical 
change, 108. 

Solvent used in heliography, 12. 

Somerville, Mrs., on magnetizingpower 
of violet ray, 5. 

Sparaxis tricolor var, 67. 

Spectnun, theoretical, 112. 

di\-ided by Becquerel, 133. 

bleached by iodine, 297. 

Stands, levelling, 192. 

Stereoscope, the, 305. 

Stewart's calotype process, 218. 

Studies, photographic, recommendation 
for, 198. 

Sublimate, corrosive, as a fixing agent, 

Sulphocyanate of potash, 52. 

Sulphuretted hydrogen used to pre- 
pare paper, 87. 

Sun-drawing, note on the term, 11. 

Talbot's, Henry Fox, photogenic draw- 
ings, IS. 

description of the calotype, 25. 

instantaneous process, 31. 

process of photographic en- 
graving, 314. 

Theomography, 151. 
Thomas', Mr., collodion process, 263. 
Towson, Mr., on portraiture, 96. 
Transparent bodies, refraction of light 

by, 167. 
Tunny, Mr., developes with iron salts, 


Unsized and sized papers, 179. 

Valicour's bromide of iodine, 238. 
Varnished paper for photography, 30. 
Verignon on positive photographs, 295. 
Viola odorata, 67. 
Violet ray, magnetic power of, 5. 
Vogel, M., action of light on fat, 8. 

, Do. on corrosive subhmate, 8. 

Wax-paper of M. le Grey, 95. 

■ process, 227. 

, to render sensitive, 229. 

"Wedgwood's method of copying paint- 
ings on glass, 6. 

Wheatstone on the stereoscope, 305. j 

Wollaston, Dr., on the decomposition 
of gum-guaiacum, 5. 

Wood, action of chlorine and iodine 
on, 90. 

Wood's, Dr., on catalysotype, 75. 

Woolcott's American mixture, 240. 

mirror camera, 99. 

Yellow glasses, action of, 135. 
Young, Dr., experiment of, 8. 

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