Pho-tog′ra-phy
The art of producing pictures of natural scenes and objects, or of copying delineations and multiplying them, by the agency of light.
Photography depends upon the chemical or molecular changes which the rays of light effect or excite in certain substances.
It is now known that a great number of bodies are
photo-chemically sensitive in a greater or less degree, but some of the salts of
silver, and of
chromic acid in conjunction with organic matter, are preeminently so, and are used practically to the exclusion of all others.
The fact was noticed by the alchemists, that
horn silver (fused chloride of silver) suffered discoloration by exposure to the sun's rays; but the Pomeranian chemist, Sheele, in 1777, was the first to consider philosophically the
action of sunlight upon certain compounds of silver, and especially to draw attention to the activity of the
violet and blue rays as compared with the rest of the spectrum.
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Ritter, in 1801, proved the existence of
dark rays beyond
the violet end of the visible spectrum, by the power they possessed of blackening chloride or silver.
Wollaston also published some experiments on the changes which light produced in
gum-guaiacum, corroborating
Ritter's views as to the activity of invisible rays.
Wedgwood, the great potter, was the first person who made any attempt to use sunlight for
copying or delineating objects. In 1802 he contributed a paper to the Journal of the
Royal Institution of
England, entitled “An Account of a Method of copying Paintings upon Glass, and of making Profiles by the Agency of Light upon Nitrate of Silver; with Observations by
H. Davy.”
He used white paper or white leather moistened with a solution of nitrate of silver, dried, and kept in a dark place.
This, on being exposed to light, passed through different shades of gray and brown and became at length nearly black.
When the shadow of any figure is thrown upon such prepared surface, it remains white while the exposed parts become dark, therefore a painting upon glass or an engraving used as a screen above such prepared paper or leather gave a copy the reverse of the superimposed design as regards light and shade.
The images given by the camera-obscura
Davy found to be too faint to produce an effect upon paper prepared with nitrate of silver, but the
solar microscope was used with success.
All the pictures made in this way had to be carefully preserved from daylight, or the whole surface would blacken, as a necessary consequence, and neither Wedgwood nor
Davy ever overcame this difficulty, or found means to
fix such photographs and render them permanent.
To Wedgwood, however, must be accorded the honor of having been the first to produce a
photograph, in the artistic and technical sense of the word.
Dr. Thomas Young, the originator of the undulatory theory of light, published in 1804 some important researches on the chemical rays.
In 1809,
Gay Lussac and Thenard made the exceedingly valuable observation, that a mixture of
chlorie and hydrogen did not combine in the dark, whereas in diffused daylight they did so rapidly, and in sunlight with explosion.
Berard, in 1812, made a comprehensive and valuable series of investigations, which was reported on by Berthollet, Chaptal, and
Biot, acting as a commission.
By them the solar emanations were first regarded as consisting of
calorific, colorific, and chemical rays.
In 1814,
Joseph Nicephore Niepce, of Chalon on the Saone, directed his attention to the production of
permanent pictures by light.
He experimented privately for many years, and in 1827 presented a paper to the Royal Society of
London on the subject of his invention; but as he kept his method secret, it could not, according to their laws, be received.
Niepce called his process
Heliography, and some specimens of his art on plated copper and pewter plates are still preserved in the British Museum.
The sensitive substance with which Niepce worked was
asphaltum, also called bitumen of
Judaea, the remarkable properties of which he appears to have discovered.
He proceeded by preparing a solution of the mineral pitch in essential oil of lavender; with this he coated a plate of metal or glass, and when the varnish so applied was dry, he exposed it under an engraving or in the camera-obscura.
The action of sunlight for many hours was necessary before the latent image was fit for
development, to accomplish which he used a solvent (consisting of
oil of lavender and naphtha) for the unsunned portions of the coating.
By treatment with this menstruum, the picture made its appearance, the insoluble portions of the bitumen representing the lights, and the surface of the plate the shadows of the design.
A final washing with water was used to remove the traces of the solvent which covered the plate.
The work of this experimenter, judged by our present standards, was doubtless crude, but it is probable that the results he really aimed at were not limited to the making of photographs alone, but extended to the production of
engraved or
etched plates for printing purposes, an endeavor which justified him in continuing the use of asphaltum.
It is also worthy of remark, that his discoveries formed the basis of a long series of trials in the direction of
photo-engraving by his nephew
Niepce de St. Victor and others, at a comparatively recent period; and of the earliest
photolithographic process, in 1852, that of Lemercier, Barreswill, and Lerebours, working conjointly.
From another point of view, we are justified in according him a high place as a pioneer, because his pictures might well be regarded as
carbon prints in chemical composition, and as certainly permanent; excelling, in this respect, ordinary photographs, and ranking with the finest developments of the photographic art of the present day. No other attempt at the reproduction of carbon prints was made for thirty-five years after his time.
In 1829,
M. Niepce associated himself with
M. Daguerre, and no doubt contributed much to the latter's beautiful process.
In the year 1834,
Mr. Fox Talbot began the investigations which finally resulted in a valuable working process.
On the 31st January, 1839, six months prior to the publication of
M. Daguerre's process,
Mr. Fox Talbot communicated his photographic discoveries, and in the following February he published a description of his method, to which, as afterwards perfected, he gave the name of
calotype. He prepared a sheet of paper with
iodide of silver, by treating it alternately with solutions of
nitrate of silver and
iodide of potassium. When dry, and just before use, he covered the surface with a solution of
nitrate of silver and
gallic acid, and dried it again, by which means he greatly enhanced its sensitiveness.
A very brief exposure of paper so prepared to light produced an effect which, though latent and imperceptible to the eye, was yet susceptible of development by a reapplication of the
gallo-nitrate of silver to the surface of the sheet.
When the picture produced in the camera or under a drawing or engraving was thus
developed, it was washed with a solution of
bromide of potassium, the effect of which was to stop all farther change due to light.
It was then washed in water and dried.
A
photograph so obtained was necessarily a
negative, but
Mr. Talbot recognized the important fact that, by the simple exposure of his calotype paper under such a negative and its subsequent development, any number of
positive prints could be produced.
To
Mr. Talbot we are therefore indebted for a method of arresting photographic action and
fixing the image; for the conception and production of a
negative, and the subsequent
printing of positive prints by light; and, above all, for the discovery of the wonderful
development of the latent image by
gallic acid.
His process, as above given, was greatly improved by himself and others, but our space does not permit of details.
In January, 1839, the announcement of
Daguerre's invention was made to the world, but no description was given until the July following, when a bill was passed in the French legislature giving him a pension of 6,000 francs, and 4,000 francs to
Isidore Niepce, the son of
M. Joseph Nicephore Niepce, above mentioned.
The pictures were produced on
silver plates or upon sheetcopper plated with silver.
The surface was first cleaned and polished with great care; it was then exposed to the fumes of dry
iodine until a film of
iodide of silver was produced upon its face.
When the proper amount of iodization was obtained, known by the color, the plate was transferred in a suitable dark slide to the camera-obscura, and there exposed in the focus of the instrument to the luminous emanations passing from external objects through the lens.
After a sufficient time the plate was carried back to a darkened room, and there exposed in a box of suitable construction to the
fumes of mercury, evaporating at a low temperature, from 140° to 170° Fah. This treatment gave rise to the gradual development of a picture, the vapor attaching itself to the exposed parts of the iodide of silver in quantities proportional to the actinic action.
The picture on the plate is now to be
fixed by immersing it in a solution of
common salt, or, better, in one of
hyposulphite of soda, which dissolves the unchanged iodide of silver and destroys the sensitiveness of the surface to light.
The plate, after being washed and dried, is finished, but it must be covered with glass to prevent its injury by friction.
The shadows of the picture so produced are formed by the highly polished silver surface, and the lights by the deposit of mercurial vapor.
Such is the
daguerreotype in its simplest form.
It is impossible to praise too highly this beautiful and wonderful process, or the intelligence and perseverance of its inventor.
Many improvements and additions were soon made, which greatly increased its practical value.
These consisted in the use of
bromine vapor conjointly with that of
iodine in
sensitizing the plates by
Goddard, in 1839; and in the addition of
chlorine by
Claudet, in 1840: the object in both cases being to shorten the time of exposure.
The success which followed these and other improvements in the art, as well as in the construction of cameras and lenses, caused the daguerreotype process to become immensely valuable in portraiture, enabling it to hold its ground in every country until displaced by collodion, about 1852 or 1853.
M. Fizeau, by the application of a
solution of gold to the fixed daguerreotype plate, rendered important service.
Not only were the results greatly improved in appearance, and as works of art gaining much in brilliancy and force, but their permanency was also assured, the metallic gold replacing the finely divided mercury in part and combining with it, so that its dissipation was no longer an evil to be dreaded.
Mungo Ponton, in April, 1839, published his discovery that paper prepared with a solution of
bichromate of potash, and dried, was sensitive to light.
Without ignoring the presence of the paper, he believed that this was true of the salt itself, but
Becquerel showed in 1840 that
organic matter must be present and in intimate association with the
chromic salt. Mungo Ponton, in his contribution to the Scottish Society of Arts, must be regarded as having laid the foundation of some of the most important photographic developments of the present day, —
photolithography, carbon-printing, collography, and
photo-mechanical printing generally; but in this connection it must be stated that Mungo Ponton often gets credit for more than he actually did, partly from the fact that his original article is but little known.
Fox Talbot, in 1852, first made the attempt to turn his and
Becquerel's investigations to practical account, in his own
photo-engraving process.
For landscape purposes the
calotype gave valuable results in the hands of amateurs, and it finally took its highest development in the
wax-paper processes of
Le Gray and
Fenton; but until glass was used as a support for negative pictures, the business of the professional landscape photographer was a poor one.
In 1848, M.
Niepce de St. Victor proposed the use of
albumen on glass as a vehicle for sensitive salts of silver, and published his method.
The value of this idea was quickly recognized,
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and the process improved by others.
Its success depended in great measure on the fact that albumen is coagulated and rendered insoluble by the nitrate of silver used to sensitize it, and that it dries finally to a very hard and transparent film, furnishing a negative from which positive photographs can be rapidly printed by light.
A consequence of this improvement was the rapid development of all
positive-printing methods on paper.
In the brilliant series of discoveries and inventions which distinguish the history of photography, perhaps the most important in its effects was the introduction of
collodion, which took place in 1850.
To
Mr. Scott Archer of
London is due the credit of the
negative-collodion process, which has made photography the most important art-industry of the world.
In justice to M. le
Gray, it should be added that he had previously suggested collodion as likely to be of service in photography.
In the autumn of 1851,
Mr. Archer published a full description of his process, which did not differ essentially from that now practiced.
Collodion is a viscid solution of gun-cotton in a mixture of alcohol and ether.
It flows easily on the surface of a glass plate, and
sets quickly to a gelatinous film, which then dries to a hard, transparent, and insoluble skin, adhering closely to the glass.
In addition to its physical characteristics, collodion is well adapted for photographic negatives because of its indifference, chemically speaking, to the sensitive salts, acting only as a medium or vehicle for their successful exposure under favorable circumstances and subsequent treatment.
Without going into the broad subject of
collodion photography, a short sketch of its leading features is here given as at present practiced.
A sheet of
glass of size suitable for the
negative to be made is thoroughly cleaned by friction with alcohol and rotten-stone, or in some other efficient way. The operator lays hold of the plate.
holding it in a horizontal position, and then pours steadily a quantity of
sensitized collodion upon its upper surface; he then causes the liquid to travel successively from corner to corner of the plate without letting it pass the edge, and pours the excess off into another bottle.
The plate, in its upright position, is rocked gently to and fro, so as to equalize any ridges or inequalities otherwise likely to form.
By this time the collodion will have
set, forming a gelatinous film, evenly covering the glass.
When the plate is thus
coated, it is
sensitized by being plunged into an upright bath containing a
solution of nitrate of silver.
The collodion used for this operation is, as above stated, a solution of gun-cotton, but it contains, in addition, certain iodides and bromides of the metals, most usually of potassium, ammonium, and cadmium, but many others are used.
The changes which now take place in the gelatinous film of collodion immersed in the negative bath will be easily understood;
metallic silver takes the place of the alkaline or other metals in the film, and forms there
insoluble bromide and
iodide of silver. The coating upon the plate, which was transparent when it entered the bath, is now milky, entangling in its substance the two haloid salts above mentioned.
The plate is next to be lifted from the bath (the room being darkened), drained for a few moments, inclosed in a
plate-holder, carried to the
camera, and exposed before the scene or model to be photographed.
During this operation, the sensitive coating receives the rays of light forming the picture, as they fall upon the
ground-glass screen used in
focusing.
They effect there a mysterious change, the exact nature of which, whether chemical or physical, is still a disputed question among the highest authorities.
The plate having been exposed to the
actinic action is now carried in the closed plate-holder back to the darkened room, illuminated by yellow non-actinic light only.
The most careful examination of the surface will be found to show no trace of alteration, but a change has nevertheless been produced.
If we pour over the surface an aqueous solution of a
salt of iron (generally the protosulphate), to which a quantity of
acetic acid has been added, the picture gradually undergoes development, a dark deposit forming upon all those places where the light has acted, the density of which is directly proportional to the energy of the chemical rays.
To explain this beautiful phenomenon, we must remember that the collodion has brought with it from the negative bath, not only the sensitive salts of silver, but also a quantity of the nitrate solution adhering to and permeating the film.
In the silver solution, the protosalts of iron, even in the presence of acetic acid, which acts as a retarder, would, in the course of time, cause a deposit of metallic silver in a finely divided state.
It is such a deposit which forms the negative picture upon the exposed plate when flooded with the developer, as above described; but the change produced by exposure gives to the sensitive salts the remarkable power of determining the comparatively rapid precipitation of the finely divided metallic silver upon them, in proportion to the change they have undergone.
Were the free nitrate of silver washed thoroughly from the plate before exposure, the solution of iron would fail to produce a picture thereon It will be seen, therefore, that the sensitive haloid salts do not themselves participate in the formation of the photographic image.
When sufficiently
developed, the farther action of the solution is stopped by profuse washing of the plate with water.
It is then to be fixed by flowing over it a solvent of the silver salts, a solution of
cyanide of potassium, or of
hyposulphite of soda; this removes the milky character of the deposit which the film received in the negative bath, leaving the picture to all appearance as though it rested upon bare glass.
The plate is now to be thoroughly washed, drained, dried, and varnished with one of the many resinous solutions manufactured for that purpose, after which it is ready for the printer.
In the foregoing description many possible and frequently used modifications have been disregarded, as tending to confuse the reader's comprehension of the phenomena, but it is necessary to mention that protosulphate of iron is not the only substance which will act as a developing agent.
Notably, pyrogallic acid, which first succeeded the use of gallic acid, as discovered by
Fox Talbot, held for many years the first place in the estimation of photographers for this purpose.
The use of proto-iron salts was originally recommended by
Robert Hunt, in 1844, and is now universal.
The use of acetic acid in the developer is to retard the too rapid precipitation of the metallic silver from the mixture of developer and nitrate on the plate; but many other substances, most of them organic, can be and are employed.
To produce
positive photographic prints from such a
negative, the following is the method used: A sheet of paper is coated upon one side with
albumen containing common
salt, chloride of ammonium, or some other soluble chloride in solution.
When dry, this sheet is floated, face downward, upon a solution of
nitrate of silver contained in a shallow glass or porcelain tray.
The action of the solution is twofold: it coagulates the albumen, rendering it insoluble, and decomposes the chloride contained in the same, replacing the alkaline metal with silver, thereby forming sensitive chloride of silver on the paper and nitrate of the alkaline metal in the bath.
The sheet is now lifted from the liquid and dried.
A suitable piece of paper so prepared is now to be exposed under and in close contact with the finished negative.
This is accomplished by pressing them together in a frame made for the purpose.
(See printing-frame.) The light passes through the negative in quantity depending on the transparency of its several parts, and produces a darkening of the silver salt in the albuminous surface proportional to its intensity.
When sufficiently exposed, the color of the paper will be dark reddishbrown, almost black in the deepest shadows.
This sheet of paper is now to be taken from the printingframe and washed in water to remove the free nitrate, after which it is subjected to the operation of
toning. For this purpose it is immersed in a very weak solution of a
salt of gold, the action of which is modified by an admixture of carbonate, phosphate, or acetate of soda, etc. The gold from this solution, which decomposes gradually, is taken up by the photographic image, substituting metallic gold for the metallic silver, forming the picture in the first instance.
The consequence is that we obtain a much more pleasing result, and one which is, at the same time, more permanent.
As in the case of the negative, this sheet has now to be
fixed by immersing it in a solution of hyposulphite of soda, which, by its solvent action, removes all unaltered chloride of silver from the albuminous surface.
This finished print is to be long and thoroughly washed in an abundance of pure water, then to be dried, mounted, and glazed or burnished in a suitable press.
It will be observed in the foregoing description, that no developer is required to produce the image (as in the case of the negative), the explanation of which is that chloride of silver in the presence of an excess of nitrate of silver is directly decomposed by the actinic rays, the nature of its sensitiveness being essentially different from that of the analogous iodine and bromine compounds.
In concluding this sketch of the positive printing process, it is well to remark that the coating of albumen, the chief object of which is to give structureless surface to the paper, is by no means essential, inasmuch as all the foregoing operations can be equally well performed on plain paper.
The
negative collodion process, with its necessary supplement, the printing of positives on paper by direct sunlight, caused a rapid and thorough change in landscape photography, the natural result of the excellence of the work produced and the great facilities offered for its rapid and cheap multiplication.
In portraiture, it was not so. Some time elapsed before it was possible to obtain portrait negatives with a sufficiently short exposure and of such quality as to enable them to compare favorably with the best daguerreotypes.
Pending the elaboration of the negative process, the
ambrotype, or
collodion positive, as it was called in
England, became popular and held its place for several years.
An
ambrotype is simply a thin collodion negative on glass made with a short exposure and developed so as to produce as white a deposit as possible on the lights.
Such a picture is not looked at by transmitted light, nor is it valuable as a negative; it is to be backed up with a black surface, generally a black varnish, and regarded by reflected light only.
Under these circumstances it appears as a positive, the deposit reflecting and the black backing absorbing the light.
Pictures of this kind are rapidly made, and finished directly from the camera, as is the case with the daguerreotype, while the cost is very much less.
They are, however, very inferior to good positives on paper, and had to make way for the latter as the negative process improved.
At the present day ambrotypes are rarely to be met with, but
ferrotypes, or
tintypes, as they are sometimes called, are pro-
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duced by a perfectly analogous process, the substantial difference being that the collodion picture is made directly upon a thin iron plate covered with a black enamel or lacquer, which protects both its surfaces from the action of the negative bath and acts the part of the black backing used in the ambrotype.
Ferrotypes are still in vogue, the quickness with which they can be produced and their exceedingly small cost making them popular with the public.
Cameras provided with a large number of lenses are employed in their production.
The trouble and difficulty in the efficient working of collodion negatives out of doors created a desire for a means of preserving a collodion plate in a sensitive condition, so as to render it unnecessary to coat, sensitize, and develop the plate where the landscape is taken.
Accordingly, a number of preservative and dry-plate processes have been invented.
In the first class, the endeavor was to cover the wet collodion with some deliquescent substance, such as nitrate of magnesia, glycerine, etc. Such processes are troublesome and unsatisfactory, and in their turn gave way to dry-plate photography.
A great many inventors have devoted much labor to this department of photography.
Fothergill, Taupenot,
Russell, and
Wortley have all produced valuable processes, but the details are too technical and elaborate for introduction here.
No dry process gives results fully equal in quality to the work from wet plates, but they offer other advantages which cannot be ignored.
As substantially different methods, by which both negatives and positives can be made, the
collodio-bromide process by
B. J. Sayce, September, 1864, and the
collodio-chloride process by G
Wharton Simpson, about the same time, deserve mention.
Sayce's was a negative process on glass:
Simpson's, a positive process.
Each produces an emulsion of the sensitive salts of silver in collodion, an excess of nitrate of silver being also present.
A surface flooded with collodion so constituted is sensitive without a bath, and may be either exposed in the camera or printed upon with a negative.
The fundamental distinction is indicated by the respective names, one using the chloride and the other the bromide of silver.
Simpson's process is much used in the production of the socalled porcelain pictures.
Notwithstanding the exquisite beauty of ordinary photographs on paper, they are subject to a reproach which takes immensely from their value as works of art, for they contain within themselves the elements of destruction, and cannot be regarded as permanent.
To overcome this difficulty, efforts have been made for the last twenty years to substitute carbon and other pigments for the fugitive tints of the photograph.
The first to experiment in this direction was
M. Poitevin of
Paris, in 1855.
He used a mixture of
bichromate of potash with organic matter, such as gum, gelatine, etc., coloring it with
lampblack or other indestructible pigment.
A paper coated with this mixture and dried suffered under a negative a change, the nature of which was to render the organic matter insoluble on the places affected by light.
A subsequent washing removed the unchanged gum or gelatine from the surface, leaving more or less intact those parts of the coating on which the light had acted and rendered it insoluble, and with it the coloring matter which had been employed.
M. Poitevin patented another
carbon process at the same time in
England, which differed from the foregoing, inasmuch as a greasy printing-ink was used to furnish the color.
This was applied as a lithographer or printer applies his ink to the exposed organic surface; and its retention, more or less perfectly by the design, depended upon the peculiar property which such altered organic matter possesses (for the elaboration of which we are indebted to this investigator) of
attracting and holding greasy substances and repelling water.
See photolithography.
Mr. Joseph Dixon published this fact in April, 1854, and to him is due the credit of priority, but
Poitevin first gave it vitality and practical importance.
Many experimenters followed
M. Poitevin.
The most marked improvement on his crude and unsatisfactory methods was practically made by
M. Fargier, who
exposed from the back of the film, and not from the face, as
Poitevin did. He acted on suggestions made by
Mr. Blair and others, who pointed out the fact that the depth to which the change to insolubility penetrated into a film or coating sensitized with bichromate depended upon the intensity of the actinic action, and when such change was superficial only, as it must be for the lighter shadows of a photograph, a subsequent washing from the face will inevitably undermine and destroy them.
Mr. Swan of Newcastle-on-Tyne made very valuable changes and improvements in
M. Fargier's method, which latter, while it gave good results, was uncertain and difficult to work.
Swan was, in fact, the
first to produce a carbon process practical and admirable in all respects, which has been and is still largely used, furnishing results which fully equal and in many respects surpass the best silver prints.
See carbon printing; gelatine process.
He prepared a
sheet of paper with a coating of gelatine and carbonaceous matter on its surface; a suitable piece of this was immersed in a solution of
bichromate of potash and dried, by which it was rendered sensitive.
After exposure, this sheet was mounted with a caoutchouc varnish, face down upon another piece of paper acting as a temporary support; the whole was then immersed in warm water, whereupon the original sheet carrying the pigmented film became detached and floated off, while the gelatine dissolved away gradually from the now exposed surface, leaving eventually the organic matter attached to the second sheet in thickness proportional to the depth to which the light had penetrated the film.
It will be seen that the tint, depending on the carbon imprisoned in the altered organic matter, will also be proportional to the intensity of the light passing through the different parts of the negative, and that the finer shades will not suffer destruction as they did in
Poitevin's method.
When the warm water had thoroughly developed the picture it was dried, trimmed, and again transferred by pasting it to the
mount where it was intended to remain, the sheet employed as a temporary support being easily disengaged from the face by the application of a little benzole.
More recently (in 1870),
J. B. Johnson made some useful modifications in
Swan's method of working, establishing what is known as the
autotype process.
Another photographic process, quite as distinct in its character as
carbon printing, but comparatively of little general interest, is known as
auiline printing, invented by
Mr. Willis,
England, in 1865.
This method is designed for copying tracings or drawings, chiefly the former, and reproducing a few copies without alteration in scale and at little cost.
Willis dispenses with the camera, glass plates, collodion, nitrate bath, etc., using only a large printing-frame.
The tracing itself is used as a screen or
cliche, under which to expose the prepared paper.
The latter is placed in the printing-frame, not in contact with the drawn surface, but with the back of the traced sheet, through which the light has to pass, so as to avoid the reversing of the print.
This is an expedient which necessarily takes materially from the sharpness of the result.
Such a process, so restricted in its scope, would hardly deserve mention were it not that the chemical reactions involved are peculiar in their application to photography.
Mr. Willis sensitizes one surface of his sheet with bichromate of ammonia, adding also other non-essential chemicals to exert an influence on the tone of the resulting picture.
After being dried in the dark, the coated paper is exposed for a short time under a positive, after which the sheet is subjected in a closed tray to the fumes of aniline diluted with benzole
The second equivalent of chromic acid in the bichromate of ammonia still existing in those parts of the coated surface undecomposed by light, reacts upon the aniline and gives rise to a dark purple-black color, which is very permanent.
It is obvious that the whole sheet would blacken in the aniline vapor, but for the exposure under the tracing, and that the action of the actinic influence is to decompose the bichromate on the parts of the sheet corresponding to the whites of the drawing, and incapacitate them for oxidizing the aniline, and thereby producing the color required to form the visible picture.
A simple washing in water is all that is necessary to fix and clear up such reproductions.
Aniline prints have a general greenish tinge over their whole surface, due to the presence of sesquioxide of chromium, resulting from the decomposition of the chromic acid.
In recording distinctive processes, reference should also be made to the efforts of
Becquerel and
Niepce de St. Victor to produce photographic pictures in color.
Their labors in this direction have been considerable, with but meager results, which can hardly be said to have gone beyond a demonstration of the possibility of getting fugitive reproductions of certain colors on peculiarly prepared surfaces.
A sub-haloid salt of silver is generally regarded as the sensitive substance required in their experiments.
In addition to the foregoing might be enumerated many mechanical printing processes depending, in their initial stages, on photographic methods.
These, however, have arrived at such importance at the present day as to exclude their consideration from the general subject, and they must be sought under their respective heads.
See photolithography; photo-engraving; photo-mechanical printing; photo-relief, etc.
In a dictionary devoted to mechanical devices and processes, it would be out of place to expatiate at length on chemical phenomena incidental to the use of apparatus.
Purely theoretical considerations, therefore, connected with photography have been ignored in the foregoing article, and the labors of
Sir John Herschel,
Robert Hunt, and others, in the early days of photography, and of such men as
G. Wharton Simpson,
Hermann Vagel, and
M. Carey Lea.
have not been given the prominence they deserve and should have had in an exhaustive treatise.
Without, however, going into theory, the attention of the reader seeking general information should be directed to the marked differences which manifest themselves in the nature of the sensitiveness of chemical compounds.
In one class, the actinic rays have power to effect at once a complete change.
This is true of the mixture of chlorine and hydrogen; of the bichromates in the presence of organic matter; of asphaltum; and of chloride of silver, when substances are present (as free nitrate) capable of combining with the liberated chlorine.
To a second class belong the iodide and bromide of silver.
The action of light upon them appears to be a sort of polarization, for want of a better word; an incipient molecular change, by virtue of which the particles affected are enabled to determine and accelerate the precipitation of certain bodies (metallic silver and metallic mercury) when offered in an extremely
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divided state, and to do this with an energy proportional to the intensity of the luminous action or its duration.
The daguerreotype and the negative-collodion process illustrate this phenomenon.
The production of the picture in both cases is by true
development, — a term often used, but not applicable in its proper and restricted sense to the bringing out of the picture after the exposure of an asphaltum surface, or of a piece of sensitized carbon tissue.
A simple solvent acts in both these cases as the agent for
removing the unaffected parts. (
Contributed to this work by Mr. J. W. Osborne,
late of Melbourne, Australia, and now of Washington, D. C.)
The first daguerreotype portrait from life was taken by
Professor John W. Draper, in 1839.
An announcement was made of it in the “
London and
Edinburgh philosophical magazine,” in March, 1840.
A full account of the operation was subsequently published in the same journal.
The first daguerreotype view taken in
America was by
Professor John W. Draper, and was a view of the Church of the Messiah, taken from a window of the New York City University.
Professor Morse learned the art in
Professor Draper's laboratory.
Daguerre made an unsuccessful attempt to photograph the moon.
Dr. J. W. Draper of New York succeeded, in 1840, in obtaining a photograph of the moon on silver plates with a telescope of five inches aperture.
He presented specimens to the
New York Lyceum of Natural History in 1840.
Professor G. P. Bond of
Cambridge, United States, made photographs of the moon, in 1850, with the
Cambridge refractor of fifteen inches aperture.
Many others followed.
Mr. Rutherford's photographs of the moon are most excellent.
Mr. De la Rue, in
England, must also be mentioned.
Mr. Rutherford of New York City has been, for some time, photographing groups of stars, by which their positions are exactly recorded, without the error of personal equation.
The groups of stars are photographed twice a year, six months apart.
The telescope takes directly a field of about two degrees.
Some of the groups contain as many as 125 stars, down to the ninth magnitude, taken upon a plate 5 1/2 inches square.
A star suspected of proper motion is placed in the center of the plate.
The plate is exposed six minutes, and then the telescope is moved slightly, relatively to the object, by stopping the clock.
The plate is then exposed six minutes longer, duplicating all the stars upon the same plate, so as to identify them from other spots upon the plate, and verify their positions.
With the micrometer, each star is determined in position by its distance from the central star, and by the angle of the line from it to the central star with the east and west line.
In order to get rid of any constant error from the direction of the telescope, stars are taken first on one side of the pier and then, when the stars are in a different position, with the telescope upon the other side of the pier.
By repeating the groups six months apart, he hopes, by and by, to ascertain the amount of parallax of some of them.
An absolute map of these groups for future use is thus obtained.
See under the following heads: —
| Actinometer. | Gaudinotype. |
| Albertype. | Gilding. |
| Albumentype. | Graphotype. |
| Ambrotype. | Gumming. |
| Amphitype. | Hallotype. |
| Asphaltotype. | Heliochromatype. |
| Aurotype. | Heliochrome. |
| Authotype. | Heliograph. |
| Autotype. | Heliographic engraving. |
| Calotype. | Heliotype. |
| Cameotype. | Hellenotype. |
| Camera. | Hillotype. |
| Carbon-printing. | Hyalotype. |
| Catalysotype. | Ink-printing process. |
| Chemitype. | Intensifying. |
| Chromatype. | Ivorytype. |
| Chronotype. | Kit. |
| Chrisotype. | Lampratype. |
| Chrystallotype. | Leggotype. |
| Collodio-chloride process. | Leveling-stand. |
| Collodiotype. | Lithotype. |
| Crossed lens. | Melanotype. |
| Cyanotype. | Negative. |
| Daguerreotype. | Negative-bath. |
| Developing. | Opalotype. |
| Diaphanoscope. | Panotype. |
| Diaphanotype. | Photo-electrotype. |
| Diaphragm. | Photo-engraving. |
| Dipper. | Photo-galvanograph. |
| Duplex type. | Photo-gelatine printing-process. |
| Dynactinometer. | Photogenic drawing. |
| Elliotype. | Photoglyphic engraving. |
| Emolliotype. | Photoglyptic engraving. |
| Enameled photograph. | Photograph-enamel. |
| Energiotype. | Photographic camera. |
| Etching. | Photographic camera-stand. |
| Ferrotype. | Photographic chair. |
| Fixing. | Photographic cutter. |
| Fluorotype. | Photographic engraving. |
| Focimeter. | Photographic head-rest. |
| Focusing-glass. | Photographic lens. |
| Foxtype. | Photographic micrometer. |
| Fuming-box. | Photographic printing. |
| Photographometer. | Porcelain picture. |
| Photography. | Positive. |
| Photoheliograph. | Pressure-frame. |
| Photoheliotype. | Print-holder. |
| Photohyalotype. | Printing. |
| Photo-intaglio engraving. | Printing-frame. |
| Photolithography. | Retouching-table. |
| Photo-mechanical printing. | Screen. |
| Photo-metallography. | Sennotype. |
| Photometer. | Sensitizing. |
| Photo-micography. | Silver-printing. |
| Photo-processes. | Sphereotype. |
| Photo-relief engraving. | Talbotype. |
| Photoscope. | Tent. |
| Photosculpture. | Tithonotype. |
| Phototype. | Toning. |
| Photo-vitrotype. | Varnishing. |
| Photozincography. | Vignetter. |
| Plate-holder | Vitrotype. |
