Towler, John. The Silver Sunbeam. Joseph H. Ladd, New York: 1864. Electronic edition prepared from facsimile edition of Morgan and Morgan, Inc., Hastings-on-Hudson, New York. Second printing, Feb. 1974. ISBN 871000-005-9
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THESE processes comprehend several operations with the persalts of iron, chromium, the salts of uranium, and the carbon process. They are very interesting, but have not as yet been applied to any useful purpose. The carbon process has not arrived at that degree of perfection which is expected in such operations.* This expression of its merits is limited to direct printing on paper by carbon or other colored media, in connection with chrome salts, etc. Photo-lithography and its congeners, that require the application of carbonaceous ink, are properly classified as photo-engraving, and will be treated as such.
Sir John Herschel discovered, several years ago, that certain of the persalts of iron, when exposed to light in connection with organic matter, undergo decomposition, and are reduced to the state of proto-salts; and we are indebted to Poitevin for numerous interesting developments in this department. For instance, the perchloride, so exposed, becomes reduced to the proto-chloride, or, as Van Monckhoven more appropriately remarks, to the state of oxy-chloride. For this purpose the sesquichloride must be quite neutral. The ammonio-tartrate, potassa-tartrate, and the ammonio-citrate of iron are much more sensitive to light than the sesquichloride, and the latter salt the most of all.
The image formed by means of these salts is much fainter than that with the chloride of silver; but it can be intensified by the application of other metallic salts. The mode of operation consists in floating the paper on the solutions in question, in the dark-room, in allowing them to dry and then exposing them afterward beneath a negative, as usual, with paper prepared with chloride of silver.
Cyanotype.--Float on a solution of the sesquichloride of iron, dry and expose; afterward wash the prints, and then immerse them in a bath of ferridcyanide of potassium. The picture will appear of a blue color in all those places where the sun has acted. Ferridcyanide of potassium has no action upon the persalts of iron; on the protosalts, however, it produces prussian blue.
Crysotype.--If the papers containing the faint image, produced on the ammonio-citrate of iron, be floated on a bath of a dilute and neutral solution of chloride of gold, the image assumes a purple tone, which becomes gradually darker the longer it is exposed to the solution.
Solutions of the other metals, such as those of silver, mercury, and platinum, also produce images which are of a grayish color. Bichromate of potash yields a picture by a similar decomposition.
The discovery of this process owes its origin to Niepce de St. Victor and to Burnett. The nitrate of the sesquioxide of uranium undergoes in connection with organic matter, when exposed to the sun, a decomposition analogous to that of the sesquichloride of iron.
The paper, without having undergone any preceding preparation, excepting that of having been excluded from the light for several days, is floated on a bath of the nitrate of uranium, as follows
|Nitrate of uranium,
The paper is left on the bath for four or five minutes; it is then removed, hung up and dried in the dark-room. So prepared, it can be kept for a considerable time.
The exposure beneath a negative varies from one minute to several minutes in the rays of the sun, and from a quarter of an hour to an hour in diffused light. The image, which is thus produced, is not very distinct, but comes out in strong contrast when developed by one of the following developers
Nitrate of Silver Developer.
|Distilled or rain-water,
|Nitrate of silver,
|Acetic acid, a mere trace.
The development is very rapid in this solution; in about half a minute it is complete. As soon as the picture appears in perfect contrast, the print is taken out and fixed by immersion in water, in which it is thoroughly washed.
Chloride of Gold Developer.
|Chloride of gold,
|½ a drop.
This is a more rapid developer than the preceding. This print is fixed in like manner by water, in which it must be well washed, and afterward dried. When dried by artificial heat the vigor of the print is increased. Prints that have been developed by the solution of nitrate of silver may be immersed in the gold bath, which improves their tone.
The picture may be developed, also, by first immersing the prints in a saturated solution of bichloride of mercury, and afterward in one of nitrate of silver. In this case, however, the time of exposure is increased.
Pictures may be obtained also by floating the papers on a mixture of equal quantities of nitrate of silver and nitrate of uranium, in about six times their weight of water. When dry, they are exposed beneath a negative. In this case the image appears as in the positive printing process with chloride of silver, being effected by the decomposition of the nitrate of uranium, which, reacting on the nitrate of silver, decomposes this salt, and reduces the silver. These prints require fixing in the ordinary fixing bath of hyposulphite of soda, and then washing as usual.
Float the papers for four minutes in the preceding bath of nitrate of uranium, drain and dry. Next expose beneath a negative for eight or ten minutes, then wash and immerse in the following bath
|Ferridcyanide of potassium,
In a few minutes the picture will appear of a red color, which is fixed by a thorough washing in water.
Immerse the red picture, before it is dry, in the following solution
|Sesquichloride of iron,
The tone will soon change to a green. Fix in water, and dry before the fire.
Float the papers in the following bath for three or four minutes
|Nitrate of uranium,
|Chloride of gold,
Afterward take them out and dry. An exposure of ten or fifteen minutes will produce the necessary reduction. The picture has a beautiful violet color, consisting of metallic gold. Wash and dry, as usual.
Float the papers for a minute on the following solution
|Ferridcyanide of potassium,
Dry in the dark-room, and then expose beneath a negative until the dark shades have assumed a deep blue color; then immerse the print in a solution of
|Bichloride of mercury,
Wash the print, and then immerse it in a hot solution of
Again wash and dry.
This process aims to produce a picture on paper either with lampblack or some other fine, impalpable powder. I shall discuss this subject as distinct from photo-engraving or photo-lithographic operations, although the two processes are based upon the same principle, that of the decomposition of the bichromates or the persalts of iron when exposed in connection with organic matter to the rays of the sun. The chloride of chromium and the other salts of chrome, as well as the sesqui-salts of iron, are subject to this mode of decomposition. The rationale of the operation appears to be this: the chromic acid of the chromate, or the sesquioxide in the case of iron is reduced by light into the sesquioxide of chromium, or a protosalt of iron, and thus parts with oxygen which is communicated to the organic substance with which the salts were mixed, such as gelatine, gum-arabic, etc., which in their turn become changed in properties as to solubility or insolubility, etc.
Various authors have experimented in this direction; Mungo Pouton first indicated the principle. We are indebted for the most interesting results in carbon printing to Poitevin, Garnier and Salmon, Pouncy and Fargier. In the first experiments of Poitevin, a chromate was employed in connection with gum, Gelatine or albumen. His mode of operation, as described in the Traité de l'Impression Photographique sans sels d'Argent is as follows
"I apply different colors either liquid or solid to the paper, fabric, glass or other surfaces, by mixing these colors with the solution above mentioned, (bichromate of potassa and organic matter, etc.)
" The photographic impression, on this prepared surface, is produced by the action of light passing through a photographic negative, engraving or suitable object, or finally by means of the camera. It is then washed by means of a sponge and an abundance of water. The albumen or the organic matter becomes insoluble in the parts where the lights have acted, and the picture is produced by the color employed."
A second method is described as follows
" In the preparation of the papers I cover them with a concentrated solution of one of the substances above mentioned (gum, gelatine and the like) in connection with a chromate; after drying I submit them to the direct rays of the sun or to diffused light beneath a negative of the object to be copied. After an exposure, which varies according to circumstances, I apply by means of a pad or a roller a uniform film, either of typographic or lithographic ink, previously diluted, and then I immerse the sheets in water. It is now that all the parts, which have not been impressed by light, give up the greasy substance, while the others retain it is proportion to the quantity of light that has passed through the negative."
The principle involved in these two operations is quite different, although the result is the same. In one the film of gelatine, etc., where it has been exposed to the sun, has become insoluble in water, and consequently retains the coloring matter from being carried away in the washing. In the other case the film that has received the impression of light, has received a new power, that of adhering to the greasy ink applied uniformly to the whole surface, whilst the other parts, having no attraction for this ink, allow it to be dissolved off when floated on water.
All the other carbon processes, as for instance, that of Testud de Beauregard, of Pouncy, Chardon, Salmon and Garnier, Lafon de Camarsac, and of Fargier, are mere modifications of Poitevin's process, with but little amelioration.
Testud de Beauregard took out a patent for his process in November, 1858. It will be unnecessary to describe this process, because it is essentially analogous to Poitevin's where he makes use of printing ink.
Take a drachm of lampblack, reduce it to an impalpable powder and pass it through a muslin sieve; mix it intimately with half an ounce of a concentrated solution of gum-arabic and the same quantity of a similar solution of bichromate of potassa. Lay on a uniform layer of this mixture upon a piece of a paper fixed on a stretcher, by means of a camel's hair pencil; as soon as it is dry, it may be exposed beneath a negative to the sun's rays for a number of minutes, (from four to eight.) The print is then immersed in water, impression side downward, and left for five or six hours in this fluid. Finally it is washed beneath the tap. The gum and the coloring matter are retained in those parts that have been impressed; whilst on the others they are dissolved or washed off.
Take a sheet of tracing paper, made transparent by varnish or oil, and coat it on one side with a solution of gelatine. When dry it is ready to receive a coating of printing ink of the consistence of cream. This ink, as far as I have been informed, consists of a mixture of lampblack, or some similar material, together with asphaltum or bichromate of potassa, or with both. The quantity of the latter is very small by reason of its insolubility, in the other ingredients. This ink is brushed over the surface that has been covered with gelatine, and is then hung up to dry. This part of the operation has to be performed in the dark-room. The paper, when dry, may be preserved for months unchanged, if not exposed to the light.
The next operation is to expose the prepared paper beneath a negative to light. Penney has availed himself of a method of exposure first suggested and used by Fargier, as will be seen in one of the following pages. The negative is laid in the printing-frame as in the ordinary printing of positives; upon this place the prepared paper, but with the white surface upon the film of the negative, and the surface covered with gelatine and sensitive. ink away from it or on the opposite side.
The light, therefore, has to pass both through the negative and the transparent paper before it arrives at the sensitive film. The time of exposure is about half an hour.
Wherever the light impinges upon this film, it indurates the ink and renders it insoluble in turpentine or benzine. In this process the middle tones are produced with great accuracy and beauty.
After exposure there is no apparent change in the film; but when the paper is dipped in turpentine the soluble parts are all dissolved off: The paper is next placed in a second bath of turpentine where the lights are thoroughly cleansed of ink.
The paper is then taken out and dried. The paper being transparent, the picture is seen through it, and then regarded as a true picture, free from inversion. These prints can be used as transparencies, or can be transferred to cardboard or stone. In the former case they look like wood-cuts or engravings, combining at the same time all the beauty of the photograph.
This discovery of Pouncy's has been published without the necessary details, just as these sheets are passing through the press; but if the results are as stated by good authorities, it may be regarded as the great discovery, not only or the year, but of the age. Neither silver nor gold is required in the process-the prints appear in printing ink after developing, fixing, and washing in turpentine.
For one of these processes a part of the Luynes second prize was assigned to the authors in 1858. Their other process was not brought into competition, although it was patented. Poitevin took the first gold prize.) In both processes a transparent positive is employed instead of a negative.
No. 1.--Dissolve thirty drachms of loaf-sugar in thirty drachms of water, then add seven drachms and a half of neutral bichromate of ammonia, pulverized and dissolved in a mortar.. To this mixture add ten drachms of the white of egg previously well beaten up together with a few grains of the bichromate. As soon as all these ingredients have been very intimately mixed, the solution is passed through a linen filter for use. In the mean while the paper is fixed on a board by means of tacks, and then brushed over with the above mixture. Take care to use of the mixture only just enough to cover the surface in order thus to obviate streaks and other similar imperfections. The paper is then removed and dried before the fire, taking care not to bring it too near, and to present the posterior side to the heat. This part of the operation is soon finished. It is then exposed beneath a positive to the rays of the sun for fifteen or twenty minutes. After the expiration of this time the image is quite visible; the paper is again heated before the fire, which appears to continue the action of light, and thus becomes the means of modifying the intensity of the shades. It is now fixed a second time upon the board, and fine ivory black is brushed over the surface with a flat, moderately soft and flexible camel's hair brush. The film of ivory black is afterward uniformly spread by means of a soft pad of cotton all over the surface, after which the paper is detached from the board and presented for a few seconds to the fire. This being done, the paper is cautiously immersed in water, picture-side upward, and left there for a quarter of an hour, moving it about gently at intervals. As soon as it is supposed that the soluble portions of the bichromate have been removed by the water, the paper is withdrawn. Finally, in order to improve the whites, the paper is immersed in a bath containing ten ounces of water and half an ounce of concentrated sulphurous acid. This operation has to be performed, in like manner with the preceding, with great care, otherwise the coloring matter is liable to be carried off from the parts which are insoluble, for the film does not adhere with much tenacity. The object of this final immersion is to remove a number of yellow and gray patches in the lights; with the greatest care, however, it is very difficult to get rid of numerous small particles of charcoal imbedded as it were in the porous structure of the paper. After this operation the paper is taken and dried.
Sulphurous acid may be prepared for the preceding operation, by heating a mixture of sulphuric acid and small fragments of wood, such as chips or matches, in a retort. The vapor thus produced is sulphurous acid, which can be condensed in cold rain-water to saturation.
No. 2.--In the second process a thick solution of citrate of iron is spread evenly with a soft linen pad over the surface of a sheet of satin paper. The paper is then dried in the dark-room. It is next exposed beneath a transparent positive from ten to thirty minutes to the rays of the sun, by which an image is made apparent. This is intensified or made more vigorous by the following application. Fix the paper on a board with tacks and then with a cotton pad dab the surface over uniformly with an impalpable powder of carbon or any other color. At first no change is apparent, but by breathing upon the surface, those parts that have not been impressed by light, being more or less hygrometric in proportion to the actinic action, attract the humidity and at the same time the coloring material, which exhibits the image. The parts through which light has penetrated, being no longer deliquescent, or at least only partially so, reject the carbonaceous materials, and these are swept away together with the unaltered citrate in the process of washing and fixing. The prints are afterward dried and varnished if thought necessary. The addition of sugar to the citrate in this process is recommended by Poitevin.
All these processes are more or less defective, producing prints devoid of the middle tones. This arises from the circumstance that the image is in general a mere surface picture, and especially as regards the middle tints. In the washing, therefore, these are apt to be annihilated together with the soluble film beneath them. This defect had been noticed and the cause assigned by Laborde as well as by Poitevin; and it is probable that Fargier eliminated his process on the hints thus published. The difference in his mode of manipulating consists essentially in separating the film containing the image from the glass upon which it was formed, and in fixing it on a piece of gelatinized paper the other side up. The chemical and actinic part of the operation remains the same as in Poitevin's.
Make a mixture of two drachms of white gelatine dissolved in two ounces and a half of water, and fifteen grains of lampblack, (previously washed with carbonate of soda, and afterward with hydrochloric acid, in order to remove all fatty or resinous matter;) to this mixture add a few drops of ammonia in order to decompose the alum contained in the gelatine and finally fifteen grains of bichromate of potassa. The mixture, when the ingredients' are thoroughly dissolved, is filtered through a linen cloth, and after it is made hot, it is poured upon a properly cleaned glass, and the films dried by a gentle heat.
The glass, thus prepared, is exposed for a few seconds to the light, and then beneath a negative to the rays of the sun.
The first exposition to light for a few seconds is to render the whole surface of the gelatine slightly insoluble. The second exposure beneath a negative produces an insolubility more or less deep according to the luminous intensity and its duration. It will be easily conceived that the two surfaces of the gelatine film, that is, the upper surface and the one adhering to the glass, are in very different conditions, the former being almost totally soluble, excepting here and there where the intensity of the rays has penetrated the whole substance; whereas the exterior surface, as before remarked, is insoluble. The parts between these surfaces are more or less soluble according to the quantity and intensity of the light that has passed through the negative. It will be seen, therefore, from these conditions of things, that the operation if washing, in order to be effectual, ought to be performed on the under surface. The film consequently is removed from the glass and transferred in the following manner
Flow the film on the glass plate with two coats of collodion, and then immerse it in a dish of lukewarm water. The collodion will soon be detached together with the gelatine film, which will float in the water. The film is allowed to remain until all the soluble parts are dissolved off, together with the coloring matter which they contain. By this mode of proceeding the most delicate half-tones remain attached to the collodion, and the image is brought out very perfectly. Whilst in this condition in the water a piece of paper already prepared with gelatine is brought carefully beneath the floating film and then lifted out of the water and stretched upon a board. The film, carefully adjusted on the gelatinized surface of the paper, soon adheres to it, and may thus be dried.
Without recapitulating all the various processes arising out of the use of the salts of iron, I may here mention that Poitevin has employed the gallate of iron and the sesquichloride; and that others, following in his steps, have been more or less successful in the same domain of experimentation. I will give two examples only, and refer the reader for more ample information to Poitevin interesting treatise.
Make two solutions as follows
|Sesqui chloride of iron,
Filter each solution separately, then mix and add two ounces and a half more water. Keep the solution in the dark, and use it until exhausted.
The image with carbon or any other colored and inert powder is formed on glass. For this purpose Poitevin recommends such glass as is used for stereoscopic slides, being ground on one side. If' the glasses have been used before, they are cleaned by the ordinary means recommended. Each glass is then flowed with the sensitizing solution just prepared, in the same way as with collodion or albumen, and the excess is poured off at each corner. They are then reared on one corner on pieces of bibulous paper, inclining at an angle of 60°, with the sensitized surface downward. It is better to dry the plates by rearing them up near some heated surface, otherwise the operation of desiccation will be very tedious. This operation must be performed in the dark-room. The property of the dry plates is this: by the influence of light they become hydroscopic. The plates so prepared will keep for months in boxes, as was to be expected, inasmuch as the persalts of iron have a tendency in the dark rather to peroxidize than to be reduced to Protosalts.
A plate is exposed beneath an ordinary negative varnished with copal dissolved in alcohol; all other varnishes, such as those prepared with benzine, gum, gelatine, etc., would be injurious. The film of the prepared glass and of the negative are in juxtaposition, and are placed together with great care. The time of exposure is about the same as in the common printing process. This has to be learned by practice; it is better to give too much time than too little, because the development can be stopped as soon as the image has sufficiently appeared. When taken from the printing frame the picture is already visible, white upon a yellow ground. It is exposed in the dark-room to the influence of the air, when it will be found that all those parts that have received the luminous action will become moist. In a few minutes the film will be ready to receive the first application of the carbonaceous or other inert colored material. By putting away the plates when taken from the printing frame in well-closed boxes, the development may be postponed.--The development is effectuated by dipping a very soft camel's hair pencil in the fine impalpable powder and then dabbing or rubbing it gently over the surface of the impressed plates; the image will soon begin to appear, the coloring material adhering only to those parts that have become hydroscopic by the action of the light, and consequently in proportion to the luminous impression. In general the half-tones do not appear by the first application of the powder, and it is better when this is so; for if the plate took up the color too quickly, it would be a sign that the exposure had been too long. A second application of the powder is made, and then a third, and so on, until the image is brought out iii perfect harmony of light and shade. The operation may be stopped midway without any injury to the final development, which may be completed at any convenient time. It is very easy to follow the progress of development by placing the plate image side downward on a sheet of paper, or by regarding it by transmitted light; but seen so, it is always more feeble than by reflected light. It is also easy to accelerate certain portions which are slow in appearing; all that is required is to moisten them with the breath, and then go over the parts with the pencil dipped in the carbonaceous powder. As soon as the image is perfect, it may be retained on the plate by means of a coat of varnish, and thus be used as a transparent positive, without any washing or fixing. If instead of lampblack or vegetable colors, metallic oxides or enamel powders were to be applied to the sensitized glass plate, these coloring substances may be melted in a muffle, which communicates to the surface of the glass plate a perfectly unalterable picture, similar to glass-painting; the same mode of operation may be applied to plates of porcelain. In case, however, it is required to transfer the print to paper, the operation may be performed either immediately or a long time afterward.
This operation is extremely simple, and presents no difficulty. Coat the film, containing the picture, with common plain collodion, of a consistence suitable for photographic purposes, then immerse the plate in water until the oily aspect of the film has disappeared. Next pour upon the collodion surface water acidulated with hydrochloric acid; repeat the operation two or three times. The film immediately in contact with the glass is rendered soluble in water by means of the acid, and the adherence of the collodion to the glass is at the same time destroyed. The acid is then thoroughly removed by washing in several waters, and then a piece of paper, covered with a layer of gelatine on one side and previously moistened, is placed upon the collodion and brought into contact with it by means of a large, broad and soft pencil, which is moved over it in all directions. As soon as the contact is complete and all bubbles of air have been removed, the whole is left to dry spontaneously. In the act of drying the gelatinized paper separates from the glass of itself, carrying with it the film of collodion in firm adhesion to the picture. All that now remains to be done is to varnish the surface. Copal varnish is suitable for this purpose, because it lies upon the surface of the image without penetrating the film of collodion or gelatine, and consequently never arrives at the paper beneath. The prints, thus obtained, have a very delicate and velvety appearance, the only drawback being that of lateral inversion like the negative, unless the latter has been specially prepared beforehand. But the picture can be produced without any lateral inversion, not only by having a negative in the right conditions, but by the following somewhat complicated manipulation, although equally as easy as the preceding. In this case, the collodion is applied as before, the immersion in water and the flowing with acidulated water are performed, and then a piece of moistened paper, smaller in size than the plate, is brought into contact with the collodion film, in the same way as the gelatinized paper was made to adhere. The border of film all round the paper is now raised and folded over the edges of the paper, which when raised with caution carries the whole detached film from the glass. A piece of paper covered with gelatine and larger than the plate is now moistened, upon this the detached print is brought into contact, pressed into perfect adhesion by means of the soft brush, and then the borders of the film around the edges of the first paper are folded back, when, seizing an angle of the first paper, it is easily raised from the collodion film. The picture now is no longer inverted, and is besides fixed, the coloring matter or image proper lying protected between two films, one of collodion and the other of gelatine. With a tenacious collodion this operation of double transfer is always successful; it takes in fact longer to describe it than to perform it; as to the simple transfer, it always succeeds, whatever may be the quality of the collodion.
This process, after all, is very simple and almost always certain; besides this, it entails but little expense and requires less delicacy of manipulation than other photographic processes.
For vitrification or enamel operations, it possesses a great advantage arising from the facility of folding the collodion film, retaining the picture upon curved as well as upon plain. surfaces.
Another property of the surfaces prepared with the sesquichloride of iron and tartaric acid is this: fatty substances, such as printing inks, applied after the luminous impression through a negative, adhere only to those parts that have not been modified by light.
Almost all vegetable colors may be used in this process; it will be evident therefore that pictures resisting all change from the atmosphere or from time, may be obtained of any color that may please the fancy.
This is a new process of Poitevin's. Five or six parts of gelatine are dissolved in a hundred parts of water; this solution is colored with a sufficient quantity of lampblack or any other inert color. Each sheet of paper is floated on this solution, which is kept lukewarm on a water-bath. By this means a very uniform film of color is communicated to one side of the paper, which is afterward placed flat on a horizontal surface with the colored side uppermost, and allowed to dry spontaneously. In this way a large number of sheets may be prepared beforehand.
In order to sensitize them they are immersed in a bath containing a solution of sesquichloride of iron and tartaric acid in the proportion of ten parts of the sesquichloride of iron, one hundred parts of water and three parts of tartaric acid. The papers are then allowed to dry in the dark. By this treatment the film of gelatine has become completely insoluble, even in boiling water.
These films receive the actinic impressions through a transparent positive; and in the parts where the light acts, the film becomes soluble in hot water proceeding from the surface of the film in contact with the transparent positive.
After the paper has been in this way exposed to the sun, if the positive is not very intense, (which is preferable in this kind of print,) it is immersed in hot water; then all the parts that have undergone the solar influence are dissolved in proportion to the quantity of light that has permeated the glass positive. In the places which correspond with the lights of the positive, the blackened or colored surface is dissolved to the surface of the paper, and will leave perfect whites; whereas in the half-tints, only a certain portion of the film will disappear, proceeding from the surface, and these half-tones will be reproduced by the greater or less thickness of the film of gelatine remaining insoluble. Now as this part is in immediate contact with the surface of the paper, it can not be carried away in washing. As to those parts of the positive which are completely black, they will be produced by the total thickness of the primitive film. All that is required to finish the print is to allow it to dry, and then to wash it in acidulated water in order to get rid of the salts of iron, afterward to pass it through several waters, and finally to allow it to dry spontaneously.
It is a curious fact that experiments in photographic engraving gave rise to photography itself. The idea, the most prominent in the mind of Nicéphore Niepce, when he commenced his indefatigable researches in 1813, was not only to fix the image obtained by the camera obscura on a plate of metal, but to convert this plate into an engraving from which to receive prints by the press. After the partnership concluded between Niepce and Daguerre, this idea appears to have been abandoned; and an early death removed the former, the real originator of much that is valuable in photography, before he perfected the process which he left us. This process, together with a great deal that is interesting in photographic engraving, will be found at length in a small pamphlet published by his indefatigable nephew, Niepce de Saint-Victor, the Traité Pratique de Gravure Heliographique, in 1856.
The various ways that have been taken to come to one and the same result, that of obtaining a metallic plate, resembling an engraved plate, from which to receive prints exactly in the same way as with the engraved plate, take their origin either from the Iodo-mercurio-type or plated copper of Donné, the bichromotype of Talbot, or the asphaltotype of Nicéphore Niepce, if I may thus be allowed to create new names to represent these three classes. Without adhering to historical dates, I will simply recount what has been accomplished in each class.
The first attempts that were made to convert the daguerreotype into an engraved plate by an etching liquid, were those of Dr. Donné. He first went round the edge of the plate with a varnish or wax, making a ledge so as to retain the etching fluid. This fluid consisted of aquafortis diluted with four parts of water, which, when poured upon the plate immediately after the image was fixed, but not gilt, attacked the silver parts, without injuring or altering the whites. As soon as the etching was supposed to have advanced far enough, the plate was well washed, and the varnish or wax removed from the edges. It was then ready to print from.
The specimens obtained by the engraver's press from such plates were not very satisfactory; and the softness of the silver film precluded the possibility of printing more than a few dozen from the same plate.
This process is similar to that of Donné, but it proceeds farther, and thus overcomes two very great imperfections in Donné's plates: the want of depth in the parts etched, and the extreme softness of the silver film. I will give the process as described by the originator:
" A mixed acid, composed of nitric, nitrous and hydrochloric, (the last two may be replaced by nitrite of potassa and common salt,) is endowed with the requisite properties, which is common to a solution of bichloride of copper, but in a manner less perfect.
"If a daguerreotype, whose surface is very pure, be submitted to the action of this acid, especially when hot, the white parts are not altered, while the blacks are attacked with the formation of chloride of silver, which adheres to the surface and prevents any further action of the acid by reason of its insolubility.
"Ammonia is then poured upon the plate, which removes the film of chloride, and thus presents a fresh surface to the action of the acid. By this means the depth of the shades can be increased.
" By operating in this way for several times, the daguerreotype becomes converted into an engraved plate of great perfection, but in general not possessed of sufficient depth, so that the prints on paper are not vigorous enough. It has been found necessary, therefore, to adopt other means of increasing the depth of the shades. This operation consists in gilding the prominent parts or the lights of the engraving, and to leave the silver in the etched parts intact; by which means the depth of the etching can be increased afterward by a simple solvent of silver.
"In order to obtain this result, the plate engraved as just described is rubbed over with a drying oil, as for instance linseed oil, then wiped in the manner of copper-plate printers. In this way the oil remains in the cavities alone and forms a varnish which soon dries.
"Gold is next deposited by galvanism upon all the parts of the plate excepting those filled with the linseed varnish, which is afterward removed by caustic potassa. The result of this is that all the prominent parts of the plate are protected y a film of gold; whereas the excavated parts present denuded silver.
" It is now easy by means of nitric acid to act upon these hollow parts alone, and thus increase the depth ad libitum. Previous to this treatment, however, the plate is covered by what is denominated by engravers the resin-grain., which produces in the metal those numerous inequalities denominated aqua-tinta granulations.
"From the result of these two operations the daguerreotype plate is transferred into an engraved plate resembling the aqua-tinta plates, which like these is in a condition by impression to furnish a number of prints.
"But since silver is a very soft metal, the number of impressions would be very limited, if soave very simple means were not devised to remedy the speedy destruction of the photographic plate when submitted to the operations of the press.
"This end is attained, previous to banding the plate over to the printer, by covering its surface with a film of copper by the electrolitic process. In this way it is evident that the film of copper alone bears the wear and tear produced by the labor of the pressman. If this film should happen to be damaged to any considerable degree, it may be entirely dissolved off by means of a dilute acid, without injuring the silver on which it is deposited, when the plate may again be covered with copper, and rendered as good as new."
Plates of copper, steel or zinc are employed in this process. These are first washed over with a dilute solution of sulphuric; acid in order to remove the film of oxide, then well rubbed with a mixture of carbonate of soda, and well dried. A solution of bichromate of potassa and gelatine: is then flowed over the surface, and dried by the application of heat until the film assumes a beautiful yellow color. This operation is performed in the dark-room.
|Saturated solution of bichromate of potassa,
Mix the two solutions and filter. The mixture will keep for some time. In summer it is sufficiently fluid; but in winter it requires to be warmed before it is flowed upon the plates. It must lie preserved in a dark place. The proportions alcove given are found to work well, but they may be changed, however, without altering the result. The color
of the film is pale yellow and generally bordered with narrow fringes of prismatic colors. If the whole surface is covered with this prismatic appearance, it indicates that the film is very thin, perhaps, if any thing, too much so for successful manipulation.
The transparent positive or other object is now placed the printing frame and the prepared plate upon it. An albumen photograph is the best adapted for such operation because: the film is the least liable to be damaged. The two are in juxtaposition. An exposure of two or three minutes to the rays of the sun will produce a picture whit: will appear yellow on a brownish background. A longer exposure is required in diffused light; the amount of which will have to be modified by experience.
The next operation consists in covering the film of the plate when removed from the printing-frame with very fine copal or resin powder. This part, of the work has to be performed with great care and uniformity. It is frequently effected by placing a heap of the finely pulverized material on the bottom of the box and then with a pair of bellows to make a cloud of the dust in which the plate is placed. The object of this operation is to communicate to the plate the aqua-tinta granulation. If the film of copal or resin be too thick, the etching fluid will not be able to penetrate to the metallic plate beneath. The plate thus covered with the powder is heated over an alcohol lamp in order to melt the copal. The fusion is known to be effected by a change in the color. The plate is then allowed to cool. The ordinary way of producing an aqua-tinta foundation is to project the resinous powder on the denuded surface of the metal; in this case it is on the surface of the gum itself; and it is found to act well.
The etching fluid is prepared as follows: Saturate hydrochloric acid with sesquioxide of iron by means of heat. The solution is filtered and evaporated until when cooled it becomes a concrete mass, which is preserved in well-stoppered bottles. It is a very deliquescent salt. With this salt prepare three solutions in the following manner
No. 1. Saturated solution of sesquichloride of iron in water.
No. 2. Contains five or six parts of No. 1 to one of water
No. 3. Contains equal portions of No. l and water.
The stronger the solution, the less effective in etching; the right strength can. be learned only by experience. Make a trial as follows: Pour a small quantity of No. 2 upon the plate and spread it with a camel's hair pencil. It is not necessary to have an elevated border of wax around the plate, because but a very small quantity of fluid is used, and there is no danger of its flowing over the edges of the plate. The etching fluid penetrates the gelatine where the light has not acted, and this penetration is in proportion to the deficiency of the luminous action. On this remarkable property is founded, in a great measure, the art of photographic engraving. After a minute or so, the engraving begins to show itself by turning dark, brown or black; and soon the effect extends over the whole plate. The details of the picture appear with great rapidity in each part. This rapidity must not be too great, and, where there is a tendency in this direction, the progress of the etching must be impeded before it has acquired a sufficient depth, (which requires an action of a few minutes' duration.) If in these preliminary experiments it be found that this tendency prevails, the solution No. 2 has to be modified by the addition of a portion of the saturated solution No. 1, before No. 2 can be employed in the etching of afresh plate; but if, on the contrary, the engraving fails to appear after the lapse of a minute, or if it commences but proceeds too slowly, it is a sign that the liquid No. 2 is too strong or too near its saturation. This deficiency is corrected by adding a little water before it is employed for a second plate. In making this correction the operator must not forget that a small quantity of water often produces a great difference and causes the etching to proceed very quickly. As soon as the strength of No. 2 has been appropriately graduated, which in general requires three or four experimental trials, it may afterward be employed with safety. In this case the plate is flowed as before indicated, and the operation proceeds until all the details appear and present a satisfactory aspect to the eyes of the operator, which takes place generally in two or three minutes, the etching liquid being kept moving over the surface all the time by a camel's hair pencil. As soon as it appears probable that the engraving will not be any better, the operation is stopped, by wiping off the fluid with a pad of cotton or of wool and afterward flowing the plate with a sheet of cold water. The plate is then wiped with a clean linen cloth, and afterward rubbed with soft Spanish white and water in order to remove the gelatine. The engraving is now complete.
Another method by the same author is the following: When the plate is ready for etching pour upon it a small quantity of No. 1, the saturated solution. This may be left on the plate for a minute or two. No apparent effect is produced by this operation, but it acts beneficially by hardening the gelatine. After this it is poured off aid a sufficient quantity of No. 2 takes its place and produces the etching already described, which, on its appearing satisfactory, requires nothing more to be done.
But it frequently happens that a few patches of the engraving, such as distant mountains or vessels in a landscape, refuse to appear, and as without these the engraving would be incomplete, it is recommended to apply, by means of a camel's hair pencil, a little of No. 3 to those parts, without pouring off No. 2. This simple means is frequently effective in bringing out the details of the picture, and sometimes with great rapidity, so that the operator his to be very cautious lest this fluid might corrode parts that are to remain white. With proper skill this mode of strengthening certain parts will be found of great advantage in bringing out portions which probably would remain invisible
The substance used to produce the image on the plate under the influence of light is asphaltum or the bitumen of Judea. The process of Nicéphore Niepce has undergone various modifications by his nephew Niepce de Saint Victor. The solution of asphaltum was formerly applied by means of a roller covered with leather, or of a pad of cloth or leather; it is now applied like collodion.
Varnish of Niepce de Saint victor.
|Essence of citron-peel,
|Pure bitumen of Judea,
In order to render the benzine more anhydrous, place a quantity of freshly prepared chloride of calcium in the vial which contains it, and shake the mixture frequently. In twenty-four hours it may be used.
Asphaltum or the bitumen above mentioned dissolves very easily in benzine; it is necessary, however, to shake the mixture, and then to allow it to settle for a day or two, after which the more liquid part is decanted and filtered in order to remove all insoluble particles. The varnish is then very fluid, and produces a very thin film. The thinner the film, the more sensitive it is to light. If a thicker film be required, it is obtained by removing the stopper of the vial for a while, and allowing the varnish to evaporate, or by adding three or four parts of asphaltum instead of two. But a thick film presents more resistance to the etching fluid, and there is a limit to its application, otherwise the half-tones will be entirely wanting. The bottle containing the varnish must be kept filled and well closed, and be preserved in a dark room, if it is to be kept some time. It is better, however, to prepare only a small quantity at a time for present use.
Plates of steel, copper, zinc or of glass may be used in this process. The first conditions, naturally, for all such operations of contact-printing, are, that they be perfectly plane and well-polished. Whether direct from the planing-machine or from previous use where it has failed to succeed, the plate of steel, for instance, is cleaned with benzine in order to remove all greasy material, then rubbed with a pad of cotton dipped in alcohol ninety five per cent strong, and very fine emery powder. By this means the steel can be polished as bright ht as a daguerreotype plate. Copper and zinc plates as also those of glass are polished with rotten-stone. Immediately before use it is well to cover the steel, etc., plate, with a coating of rotten-stone and alcohol, allow the film to dry and then to rub it off; afterward use the broad camel's hair pencil, as in the wet collodion process, in order to remove all particles of dust.
This operation is similar to many others already briefly described. Be careful not to shake the varnish before it is poured upon the plate, otherwise it will give rise to an infinite number of small bubbles in the film. Pour the varnish either on the middle or the upper right-hand corner of the plate, as you would collodion, and as you are accustomed to do so with success; and allow the excess to flow off at the lower right-hand corner. Invert the plate and let it lean against the wall on the opposite corner to that from which the excess was poured and with the film toward the wall. This operation may be performed in a weak diffused light; let the plate, however, dry in the dark-room, which will take place very rapidly, and use it as soon as dry; for its sensibility is now the greatest. The more uniform and thin (to a certain extent) the film may be, the greater the probability of a successful issue.
The printing operation is performed in the printing frame, only a transparent positive is used instead of a negative. A paper print maybe substituted for the glass positive, first making the paper transparent by a solution of wax in turpentine or otherwise. The glass positive is placed upon the glass plate of the printing frame; and then the prepared asphaltum plate lies upon the positive, their two films being in contact. In this the frame is exposed to the direct rays of the sun or to diffused light. The time of exposure will seldom exceed a quarter of an hour in the sun or an hour in diffused light; the right time has to be learned by experience.
This operation consists in dissolving the parts that have not been acted upon by light and thus removing them and exposing the plate beneath.
|Rectified oil of naphtha,
This solvent is poured upon small plates in the same way as collodion, or the developer, etc.; but when the plates are large, it is necessary to have a porcelain or glass dish, at the bottom and the left end of which the plate is placed. The solvent is poured upon the inclined right end, and by elevating this end the liquid flows uniformly over the whole plate. This operation of flowing the plate must be performed immediately after the exposure, whether in the camera or by contact.
If the action of the light has been too long, a stronger solvent is needed; the strength of this solution is increased either by increasing the quantity of the benzine or diminishing that of the naphtha. If the whole of the film of asphaltum is dissolved off, the action of the light has not been either sufficiently intense or prolonged; if; on the contrary, but little has been dissolved, either the luminous action has been too long, or the asphaltum was very sensitive, in which case the image is always foggy.
If the asphaltum peels off in certain parts of the plate, it is an evident sign the plate was moist. It sometimes happens, however, that when the film is too thick, the same inconvenience takes place.
The solvent may be used several times in succession, taking care to filter it when it becomes too colored.
The picture in general appears very quickly, so that the action of the solvent has to be stopped almost immediately after its application. If the exposure has been too long, the solvent action of the varnish is not so rapid. In order to prevent all further action, the plate is plunged into a vessel of water and afterward well washed beneath the tap until every trace of the solvent and all particles of dust are removed. The plate is then allowed to dry spontaneously, or is dried by artificial heat.
The film of asphaltum, unfortunately, is not quite impermeable to the action of the etching fluid used afterward. Various means have been resorted to so as to obviate this difficulty. Wax is sometimes added in small proportions to the varnish to remedy this evil. The best result is obtained by subjecting the plates after development to the vapors of the essence of lavender or spikenard. For this purpose an arrangement is required similar to those used for iodizing the silver plate in the daguerreotype process. At the bottom of this vessel a small porcelain capsule is placed containing the pure essential oil not distilled or rectified, which is heated from below by means of a spirit-lamp to the temperature of about from 150° Fahrenheit to 170° at the most, lest the oil should be volatilized in too large a quantity. In the first place let the fumigator be filled with vapor, then introduce the plate and keep it there for two or three minutes. The same essence may be used a second time, but no more.
The color of the film after fumigation, when successful, must be the same as before it has been acted upon by the light, bronzed and iridescent.
The plate is then dried by exposing it a moment to the air before the etching fluid is applied, and if the operation of fumigation has been properly timed and conducted, the film, has become quite impermeable. It is necessary to guard against carrying the deposition of the essential oil too far, otherwise the acids will have no action whatever upon the metallic plate.
This operation is indispensable for plates obtained direct either by contact or in the camera from a photograph, a landscape or portrait, etc.; if the plate be copied from an engraving, it is not necessary. Without this expedient the plate will not retain the ink.
The grain is applied in the following manner: Resin reduced to an impalpable powder is placed at the bottom of a box made for this purpose, which, by means of a pair of bellows, is raised into a cloud, and thus, when it settles on the plate, communicates to the latter the granular condition denominated aqua-tinta. The plate is then heated, whereby the resin becomes melted and forms a sort of network over the whole surface. This operation gives the shades a grain more or less fine, (according to the impalpability of the powder,) which retains the printing ink, and thus permits numerous impressions to be taken of the plate as soon as the varnish and the resin have been removed by the aid of fatty bodies and essential oils or benzine.
It would be useless to attempt to etch a plate where the conditions are not appropriate. The film must have a brilliant and iridescent appearance, be sufficiently impermeable to the acid employed, free from fogginess, (that is, the. metallic plate must be completely denuded in the deep shadows and partially so in the half-tones,) and the aqua-tinta grain must have been communicated to it. This being the case, proceed as follows
Raise a border of mastic all round the edge of the plate, and varnish those parts that are intended to be quite white in the print, as is practised in ordinary etching. Next pour upon the film a dilute solution of nitric acid, beginning with one per cent of acid, and strengthening it to as high as twelve per cent, according to the resistance of the varnish and the depth of etching required. The etching fluid has to be changed, without increasing the per centage of acid; for it frequently happens that the plate resists the action of the fluid for some time, and especially if the film has been fumigated with the essential oil of spikenard. Very good results may be obtained by pouring hot water over the plate before the acid is applied; but in this case be sure to remove every bubble of water from the interstices by blowing before you pour on the etching fluid.
As soon as the etching is supposed to have advanced far enough, all further action is suppressed by dipping the plate in cold water; this must be clone in time, otherwise the varnish would be attacked in those parts that ought to be preserved, a circumstance that sometimes happens, for which unfortunately no definite cause can be ascribed. To obviate this difficulty a saturated solution of iodine in water at 60° is used as an etching fluid, instead of the aqua-fortis. The fumigation is omitted; and the iodine solution is poured upon the plate and kept there for ten or fifteen minutes, until it becomes nearly colorless; this operation is repeated two or three times, until the etching is regarded as deep enough or nearly so; it is then terminated by employing a dilute solution of aqua-fortis, which completes the etching without attacking the varnish.
Copper requires a much stronger etching fluid than either steel or zinc, and iodine can not be used in this case; it has therefore been recommended to etch the parts by galvanism.
The plates in general require touching up with the graver, especially if copied from photographs; whereas distinct pen and ink drawings or plans or maps may be engraved in the way prescribed, without requiring the aid of the graver's tool.
Etching on glass is performed, when the plates are prepared, by placing them with the film downward over the fumes of hydrofluoric acid. For this purpose a box is constructed of lead, of the size and shape of the plate, and about two inches deep. At the bottom of this place a small saucer of lead containing pulverized fluor spar and sulphuric acid intimately mixed. Cover the box with the inverted and prepared plate as a lid, and apply heat to the bottom of the leaden box by means of a spirit-lamp; fumes of hydrofluoric acid will be set at liberty, and will corrode those parts of the glass that have been denuded by the solvent.
The plate, prepared either with asphaltum or the bichromate of" potassa and gelatine, is subjected to the luminous impression beneath a positive instead of a negative. After exposure and washing, the plate is attached to the negative pole of a battery and immersed in a solution of gold for electrolytic purposes. In this way the lights of the design are protected with a film of gold, the middle tones are partially covered, and the blacks only just sufficient to communicate a sort of reticulated structure which forms the necessary grain.
The metallic plate, the wood, stone or glass is first covered on both sides with a varnish quite impermeable to the action of acids; it is then flowed on the prepared surface with iodized or bromo-iodized collodion, and treated in every respect the same as a glass plate for the reception of an ambrotype; that is, it is sensitized in the bath of nitrate of silver, exposed in the camera, or by contact with an albumen, etc., print on glass to the view, etc., developed, fixed, washed and dried. Finally, the surface of the picture, thus obtained, is covered with a solution of dextrine to preserve it from injury. The plate, etc., is now ready for the draughtsman, and when prepared by him by means of a fine-pointed style, it is submitted to the etching fluid, as before directed.
These branches have been brought to a high degree of success within the last two or three years. They are not yet quite perfect; the want of perfection consists in the in. ability to obtain easily and uniformly the middle tones. Drawings in pen and ink, maps, plans, pages of letter press, etc., in which there is no intermediate tones between the lights and shades, are executed to any amount of reduplication by the photo-lithographic process, and very successfully; but landscape scenery, architecture and portraiture, where there is a regular blending of light into shade, can not always and at will be reproduced satisfactorily by any of the known processes of photo-lithography or photo-zincography, although it must be confessed that the specimens published in the work on Photo-zincography by Colonel Sir Henry James indisputably prove the possibility of the accomplishment of this desideratum.
The various processes practised in this department of photography depend upon the properties of asphaltum, the persalts of iron, and of chrome already frequently alluded to; and the object to be attained consists either in preparing surfaces where the shades are etched out as in the copperplate, or in relief, as in common type.
In some processes the designs are taken directly upon stone or zinc; in others on prepared paper, and afterward transferred to stone or zinc. By the latter the picture is obtained in a direct position; whereas by the former, without previous arrangement, the image is inverted.
This process was originally employed by Nicéphore Niepce in the production of heliographic engravings. The first attempts in photo-lithography were made at the suggestion of Barreswil, in connection with Lemercier, a lithographer, and Lérebours, an optician. Davanne, too, co-editor with Barreswil, of the Chimie Photographique, assisted in the preparation of the specimens published as early as 1853.
The properties of asphaltum dissolved in ether or in essential oil, are the following:
First. It is sensitive to light, and becomes changed in proportion to the intensity, whereby parts, not acted upon by the luminous impression, can be removed by a subsequent operation of washing with a solvent.
Second. It is sufficiently adhesive to the stone and impermeable to the etching liquids to prevent the latter from acting upon the stone, excepting on the parts denuded by the solvent.
Third. The parts of asphaltum left on the stone have an attraction for the greasy ink used in photo-lithography.
Now these are the properties required in photolithography
The stone is first prepared as for lithographic purposes, and then placed on a leveling stand and made perfectly horizontal. Next take a quantity of bitumen, reduce it to a powder and dissolve it in ether; filter as much of the solution as may be required to flow the stone. Whilst flowing the stone with this preparation be very careful to avoid agitating the air so as to set the dust in motion, or produce undulations in the film. The excess of bitumen may be allowed to flow off on the sides and corners; and where there is a tendency of the fluid to become stagnant or to flow back again upon the stone, this is prevented by the application of a glass rod to guide the superfluous fluid over the sides. The object is to obtain a thin, uniform film, which beneath a magnifying glass presents a reticulated appearance all over the stone, communicating to it what is denominated by engravers a grain. The quantity of asphaltum in ether required to produce such a thin and uniform film has to be ascertained by practice.
As soon as the asphaltum is dry., a negative is placed on its surface, (the two films being in juxtaposition,) and is held down in contact by pressure on the sides and corners by means of a pressure-frame. Any negative may be used. The stone is now exposed to the light of the sun for a time, which has to be learned by experience. This operation being concluded, the stone is taken into a room feebly lighted, the negative is removed and the surface containing the latent image is washed with ether. The parts, on which the light has acted, have become insoluble; these,, therefore, are not disturbed by the solvent; whereas all the rest of the bituminous film that has been protected by the shades of the negative, is dissolved and washed off. If the time of exposure has been too short, the image is destitute of all middle tones; it is mere black and white; if, on the contrary, the exposure has been too long, the picture is foggy, that is, the fine lines have become heavy and the stone imperfectly denuded in the lights. In order to be successful, the surface must be well washed with ether, otherwise spots will arise that can not afterward be removed.
The film is then dried, and if the image thus formed is satisfactory, the stone is then treated in the same manner as a drawing with lithographic crayons; that is, it is first flowed with a weak acid solution containing a little gum, so as to preserve the whites and give more transparency to the picture; it is then washed in several waters, and if need be, in oil of turpentine; finally it is inked with lithographic ink. If all succeeds well, the image will take the ink with facility as soon as the roller is passed over it, and will require no touching up. Prints are obtained from stones, prepared in the manner above described, as with any other lithographic stone; they improve gradually after a number of impressions have been taken. The authors, whose process I have copied, assert that they have prepared a number of stones by this process, that have given great satisfaction and have not been worn out quicker than any ordinary lithographic impression.
The mixture proposed by Talbot of bichromate of potassa and organic matter, such as gelatine, albumen, gum, etc., is used by Poitevin in the processes about to be described.
An ordinary lithographic stone is covered with a solution of albumen and bichromate of potassa, and allowed to dry spontaneously. It is then exposed to the light of the sun beneath an albumen, tannin, etc., negative, by which the parts to which the light has not been able to penetrate through the opaque shades of the negative, are preserved in their natural and soluble condition, while the parts impressed by the light have become insoluble. Thus modified, the latter parts repel water, as if the light had produced some greasy substance in the film. In this condition these parts easily adhere to ordinary lithographic ink, whilst there is no adherence between the ink and those parts that have undergone no actinic impression. A roller charged with such ink is then passed over the stone; and the image is made manifest by the adherence of the ink to the parts impressed and in accordance with the intensity of the impression. The excess of ink is removed with a wet sponge. The stone is then covered with a weak acid which acts upon the parts not imbued with ink, and thus presents the image in relief, which is treated afterward like any other ordinary drawing on stone with lithographic crayons.
Poitevin has also availed himself of a peculiarity, which gelatine in connection with bichromate of potassa possesses, of swelling when exposed to cold water and before it has been impressed by light. His mode of proceeding is as follows
A plate of glass is flowed with an even film of a solution of gelatine, which is allowed to dry spontaneously. The plate is then immersed in a concentrated solution of bichromate of potassa; and when the film has become completely permeated with the salt, the plate is quickly washed in order to remove all excess of the solution, and is put away in the dark-morn to dry. The plate is then ready for exposure beneath a negative, which must be very clear, transparent, well-defined and vigorous. After exposure it is immersed in cold water, by which the parts that have been protected beneath the dark shades of the negative, swell. In this condition the plate is moulded in plaster. This mould is afterward submitted to the electrolytic action of a galvanic battery, from which a metallic matrix may be obtained for printing from by the typographic press.
The processes above described, whatever the success in manipulation, are defective in one essential point: the pictures are laterally inverted. It is true that negatives may be obtained by copying in a condition to produce the proper effect.
A lithographic stone or a plate is covered with a solution of one quart of water, four ounces of gum-arabic, one hundred and sixty grains of sugar, and a certain quantity of bichromate of potassa. The stone is then put away to dry in the dark-room. It is next exposed either in the camera or beneath a transparent positive. The gum becomes almost insoluble by the action of the light. The stone is then washed with a solution of soap, which removes the parts that have not been acted upon by light, while the soap is decomposed in those parts where the luminous impression has been made, "the action of the soap being inversely proportional to the intensity of the light." The stone thus prepared is washed with water, and when it is dry it is covered by means of a roller with a layer of printer's ink, which, combining with the soap, adds new body to the print. When it is desired to obtain gradations of light and shade, the stone is submitted to the graining process above described; but this is not necessary where blacks and whites alone are required.
It is difficult to observe any fundamental difference between this process of Newton and the preceding one of Poitevin; it is apparently a mere copy. The remaining processes to be described are the most important and successful; they are founded upon a discovery of Asser of Amsterdam, the transfer-process, although Sutton had remarked that printer's ink, put on gelatine paper, would come away, if soaked in water, leaving the paper quite clean.
This process consists in first obtaining a picture on paper prepared with bichromate of potassa and organic matter, and then in transferring this direct picture on stone or zinc, which, being laterally inverted, yields a direct print in the press. The process has been much improved in the manipulations both by Osborne in Australia, as well as by Captain Scott and Colonel Sir Henry James, in the Ordnance Office, Southampton. Osborne, it appears, made his discoveries and improvements independently of Asser's publication, and of those from the Government office in Southampton. These processes being then essentially the same, it will not be necessary to describe more than one in this work. Colonel Sir Henry James has just published a new edition of his Photo-zincography, accompanied with very neat specimens of prints that can be obtained directly from photographic negatives by this process.
The negatives in this sort of work require above all things to be very transparent, without the slightest fogginess in the transparent parts; the opaque parts, on the contrary, must be exceedingly dense. Such negatives can be obtained only by redevelopment or Intensifying. g. The exposure of the collodion plate to light is not quite so long as for an ordinary negative, nor is the development carried on to the same extent in the first instance as for a negative; it is better to stop the action of the iron solution as soon as the picture has appeared in full brilliancy as a positive, and then to intensify afterward. For copying engravings, pen and ink drawings, maps, plans, etc., where the delineations are purely black and white, this mode of preparing the negatives is certainly to be recommended. Where there is a gradation of tone, the time of exposure and of development must be increased beyond that of a positive or ambrotype, but yet not to the same extent as for a negative.
To intensify the first sort of negative, that is, the one for copying engravings, etc., proceed as follows, as soon as it has been developed and fixed and is perfectly clear in the transparent parts
While the plate is still moist, flow it with a part of the following solution
|Glacial acetic acid,
After moving the solution backward and forward for a minute or so, pour it off into a wine-glass, and add to it about six drops of a solution of nitrate of silver thirty per cent strong, if the plate is stereoscopic size, and so on, according to the size; shake the mixture well and then flow the plate with it, and keep it in motion, and watch the progress of blackening by the light transmitted from below, as before directed and described in the article on the negative collodion plate. It may be necessary to add more silver, or even to repeat the dose of the intensifier, sometimes two or three times; this, however, is a rare occurrence if the time of exposure has been right. When the shades are quite opaque, the operation is so far complete. Wash thoroughly and examine the plate in diffused light. If the lines have become somewhat thickened, or the transparent parts slightly fogged, these evils must be remedied by Osborne's clarifying process.
Dissolve iodine in a solution of iodide of potassium to saturation; of this solution take ten or twelve drops to four drachms of water, (for a stereoscopic plate,) and pour the solution on the moist plate, and keep it in motion until the surface of the negative assumes a uniform film of a cream color. Wash the plate and flow it with a very dilute solution of cyanide of potassium. This will remove the iodide of silver and diminish the thickness of the lines and the fogged appearance of the transparent parts.
Sir H. James intensifies with bichloride of mercury, by immersing the well-washed plate in a weak solution of this salt; as soon as the surface is whitened by the action of the mercurial salt, it is washed again, and a dilute solution of sulphide of ammonium is poured over it, which changes the color to a brown-yellow. If the negative is allowed to dry, the bichloride is used, there will be less danger of filling up the lines; but the edges of the film must be varnished first, to prevent it from slipping off when it is washed.
After the negative has been intensified and is dry, it is varnished, and is then ready for use.
The following are the formula for the various solutions recommended by Sir H. James
For Cleaning the Glass Plate.
Tripoli powder, sufficient to give it the consistence of cream.
|Iodide of cadmium,
|Iodide of potassium,
|Alcohol, sp. gr., .812,
|Ether, sp. gr., .725,
Nitrate of Silver Bath.
|Nitrate of silver recrystallized or fused,
Dissolve and filter, then coat a plate with iodized collodion, and immerse for twelve hours in order to saturate the bath with iodide. If, on exposing the plate, there should be any sign of fogging, add dilute nitric acid, (one of acid to ten of water,) drop by drop, until a clear picture is obtained. If at any time the bath should be too acid, it can be neutralized by adding a little oxide of silver.
|Protosulphate of iron,
|Glacial acetic acid,
|Glacial acetic acid,
|Cyanide of potassium,
The paper suitable for this purpose must be hard, thin, and tough, of even texture, free from wooliness, and but slightly sized. Paper made from linen is the best, such as that used for bank post paper. If there is too much size in the structure, it can be remedied by steeping the paper in hot water a short time before coating it with the solution.
This solution must be quite fluid at the temperature of 100°.
|Bichromate of potassa,
|Hot water, rain or distilled,
|Gelatine, (the finest,)
|Hot water, (rain, etc.,)
Mix the two solutions and filter while warm. When about to be used let it be poured into a large flat dish, and maintained at a temperature of 100° by placing this dish in another containing warm water.
Float the paper on this solution with the right side downward for three minutes, taking care to break up all bubbles; the operation is performed in the dark-room. Drain the paper and hang it up to dry in the manner already described in the positive printing process. When dry, the paper is floated a second time and hung up to dry by an opposite corner.
The surface is afterward smoothed by passing it through a copperplate press on a hot steel plate-the rolling press with a flat plate is also quite suitable for this purpose.
The amount of exposure is regulated by the appearance of the print. When the lines appear distinctly marked, and of a dark brownish-green, the operation is complete. The time will vary with each negative, and with the light, from one minute in the sun to twenty minutes in dull weather. If the printing is incomplete, the lines will break beneath the sponge in the washing; and where the exposure has been too long, the ink (to be afterward applied) will adhere to the ground of the print.
Formula for the Ink.
|Chalk lithographic ink,
|Middle linseed oil varnish,
Melt the three latter in an iron pot until they begin to burn, stirring the ingredients all the time; finally, add the varnish and the ink, and mix intimately.
When about to use this ink, the necessary quantity is melted with a proportion of turpentine, so as to reduce it, when cold, to the consistence of thick molasses. A small quantity is laid on the printing roller, which is then worked on a stone in the usual manner, till the coating is perfectly even.
The closer and finer the lines of the print are, the thinner should be the coating of ink.
A zinc plate is inked with the printing roller, and the bichromate print is laid face downward on it, and passed through a lithographic press; by this means it receives a very even coating of ink.
After the operation of inking the print is floated on water at 90°, back downward, for five minutes; it is then placed face upward on a porcelain or marble slab, and the surface is gently rubbed with a new soft sponge dipped in gum-water. If all the previous operations have been well performed, the ink will readily leave the ground of the print remaining on the lines.
The less friction is used the better; if the ink does not easily leave the paper where it ought to do so, the print must be floated once more on the warm water, face downward, for a few minutes.
As soon as the ground of the print is quite cleared of ink, and the whites appear in the closest parts where they show on the original, the paper is thoroughly washed in tepid water to remove all the gum from the surface, so that no trace remains. It is then dried and is ready for transferring to zinc or stone.
The plates of zinc are first scraped until all inequalities are removed. A piece of a saw-blade makes a good scraper. Let it be four inches long and three wide, in the form of a rectangle. Grind the long sides quite flat on a grindstone, so that these surfaces present two sharp edges for scraping. Use the scraper as in veneering. When the surface of the zinc is thus made free from blisters, scratches, etc., grind it down flat with a pumice-stone, and smooth it with snake-stone. Finally it is grained with a disk of zinc four inches in diameter, half an inch thick, and fixed to a handle, by rubbing the disk with a circular movement over the surface with fine sand and water. The sand is passed- through a wire sieve containing from eighty to one hundred and twenty meshes in a square inch. As soon as this operation is complete, the plate is thoroughly washed and dried, and then used immediately.
Old plates are first cleaned with turpentine, then with an alkali, and finally with a mixture of equal parts of sulphuric and hydrochloric acid to twelve parts of water. The Braining, too, is repeated.
The bichromate print is first moistened between sheets of damp paper for a few minutes, then placed face downward on the zinc plate, with two or three sheets of paper over it, and passed through the press.
If the transfer print is not more than three or four days old, it will be sufficient to pass it through once; but an old print, on which the print has had time to harden, will require to pass through the press two or three times.
The sheets of paper covering the transfer are then removed, and the latter is damped with a wet sponge for two or three minutes; this causes the gelatine in the lines to swell, and makes the ink leave them more readily.
The print is then pulled carefully from the plate; and nearly the whole of the ink should remain on the zinc.
The etching liquid is prepared as follows
Bruise the galls in a mortar and steep them in the water for twenty-four hours; after which the mixture is made to boil over the fire, and then filtered.
|Gum water of the consistence of cream,
|Decoction of galls,
The phosphoric acid is prepared in the following manner: Take a bottle, three quarters full when holding a pint of' water, and insert sticks of phosphorus in the water, so that parts of them are exposed to the air above the fluid. An incision is cut in the cork to let in air. The phosphorus thus becomes oxidized, and the phosphoric acid is dissolved by the water below. In a few days the solution is sufficiently strong for use.
The etching liquid is poured on the plate, and spread over the surface with a sponge or camel's hair brush. For fine work twenty seconds will be sufficient; whereas strong lines would bear the action of a minute without injury. The etching solution is next removed entirely with a cloth dipped in water.
Finally, the transfer ink is cleared from the plate with turpentine, or if the design is weak, with turpentine mixed with olive oil and gum-water. The plate is then rolled up with printing ink, the roller being very thinly and evenly coated with it. Impressions can then be printed in the usual manner; fifteen hundred is not an unusual number for the plate to stand without sensible deterioration.
The bichromate print can be transferred to a lithographic stone in a similar manner.
When the subject admits of it, paper, enameled with zinc white, should be used, as the impressions produced are more perfect.
Formula for Zinc Enamel.
Soak for several hours, and then dissolve by heat
|Zinc white, (oxide of zinc,)
Grind with water on a slab, mix gradually with the solution of glue, and pass through a hair-sieve.
This enamel is communicated to the paper with a broad brush, and the streaks are obliterated with a flat camel's hair pencil. A second coating is applied in a similar manner, when the paper is hung up to dry.
Sir H. James remarks that, since the publication of the first edition of the process above copied from his work, he has discovered that the paper coated with the bichromate of potassa and gelatine, after exposure in the printing frame as already described, can be made to produce transfers with hat f tone or gradation of shade by using the following composition for the ink, and washing with a soft sponge moistened with tepid water without gum, and by using a very gentle hand in the manipulation.
Formula for Transfer Ink.
|Lithographic printing ink,
|Middle lithographic varnish,
This is a method of obtaining a single copy, or a, copy or two of some manuscript, plan or document, etc., on paper, without incurring all the trouble of preparing either a stone or a plate of zinc. For this purpose a negative has to be prepared, by copying according to plans already minutely described, in which the parts are not laterally inverted. This can be effected too by simply presenting the glass surface (not the collodion surface) to the view, etc., in the camera.
With such a negative and with paper already prepared with the film of gelatine and bichromate of potassa, a positive picture can be obtained in carbon ink, laterally inverted. The image is brought out precisely as described in the process of photo-zincography. It is then placed face downward on a sheet of paper and passed through a lithographic press. A sharp and clean impression is thus obtained.
Colonel Sir H. James prepares negatives on paper covered or flowed with the wet collodion process. The sensitiveness is superior to that of collodion on glass, and the negatives, when waxed, give excellent results.
A piece of crown or plate glass is selected for receiving the photograph; this glass must be as free as possible from all flaws. It is cleaned as usual, and flowed with the following solution:
|Saturated solution of bichromate of ammonia,
|20 to 30 drachms.
Mix intimately and filter in the dark-room. As soon as the plate is dry by means of artificial heat from a stove or otherwise, it is placed in contact with a transparent positive in the printing-frame. An exposure of a few seconds to the sun will show, on removal front the frame, a faintly indicated negative picture. To bring it out, an enamel color, in a very impalpable state, is gently rubbed over with a soft brush until the whole composition or subject appears in a perfect positive form. It is then fixed by alcohol, in which a small quantity of acid, either nitric or acetic, has been mixed. This mixture is poured over the whole surface, and drained off at one corner.
When the alcohol has completely evaporated, the glass is immersed gently and horizontally in a large dish of clean water, and left until the chromic solution is dissolved, and nothing remains but the enamel color on the glass; it is then allowed to dry spontaneously near a heated stove. When dry it is ready for the kiln.
Enamel of any color may be used, so that by a careful registering a variety of colors can be printed one after the other, so as to obtain a perfect imitation of a picture; also the borders of any description can be subsequently added, and the plate again submitted to the fire.
Naturally ceramic productions can be thus coated with the bichromate photograph, and afterward submitted to the fire to vitrify the image.
White enamel is glass rendered milky by fusion with oxide of tin; it forms the basis of many of the colored enamels, which receive their tinge from the metallic oxides. Thus the purple of Cassius (gold) imparts a fine ruby tint. The oxide or phosphate of silver gives a yellow color. The oxides of iron communicate blue, green, yellow and brown, according to quantity or state of oxidizement. The oxides of copper produce a rich green, and, when mixed with tartar, a red color. Antimony yields a rich yellow. The black oxide of manganese in excess forms black glass; in smaller quantities, various shades of purple. The oxide of cobalt imparts beautiful blues of various shades, and with the yellow of antimony or lead it produces green. Chrome yields greens and reds according to the state of oxidizement.
* Pouncy's New Carbon Process seems to give great promise of being usefully applied.
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