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This process gives blue impressions on a white ground from positive clichÉs, and white impressions on a blue ground from negative clichÉs. It is termed “positive ferrotype process.”
The cyanofer is an application of one of the numerous and useful inventions for which photography is indebted to A. Poitevin. In 1863 he discovered that certain organic substances were rendered insoluble by ferric chloride, and that they again became soluble; when under the influence of light the ferric chloride has been reduced to a ferrous salt. This curious phenomenon is the base of the process now to be described. As usual the process has been modified by compounding the sensitive solution in various ways and by minor details in the manner operating. But although these modifications have rendered the process easier to work with, there is not a great difference in the results obtained. We give two formulas. Aside from the addition of gum arabic, which was suggested by Mr. Pellet, and which constitutes the capital improvement of the process, the formula is substantially that devised by Mr. Poitevin.
Prepare three solutions as follows:
| A. | Gum arabic, best quality | 50 parts |
| Water | 170 parts | |
| B. | Tartaric acid | 12 parts |
| Water | 80 parts | |
| C. | Ferric chloride solution at 45 deg. BaumÉ | 35 parts in volume |
Mix gradually B to C, then C, by small quantities, in agitating briskly. It is important to prepare the solution as directed, for by adding the ferric chloride before tartaric acid, the gum arabic would be at once coagulated. When the ferric chloride is mixed, the solution at first thickens, but [pg 38] becomes sufficiently fluid for use in a certain period. It does not keep, and should be employed the day it is made if possible.
The paper, which should be well sized and calendered, and which, when not giving good results by too much absorbing the sensitive solution, must be starched as before directed, is coated either by brushing or by floating. By the first method a roll of paper five yards long can be prepared without great trouble, and give, perhaps, better results than if prepared by floating; but the latter method is by far the the most convenient: one does not generally prepare by brushing sheets of paper larger than about 30×40 inches.
For brushing, the paper is pinned on a board, then, with a large badger brush dipped in the sensitive solution, the latter is applied as evenly as possible; after which, by lightly passing the brush over, the striae are removed, the coating well equalized, and the paper hung up to dry. The coating should not be very thin, and, above all, not too thick, for then it would require an unusually long exposure to allow the light acting through the whole thickness of the film, which is a sine qua non to obtain a clear ground, i.e., not stained blue.
To prepare by floating, pour the solution in a shallow tray, which needs not to be more than 20×34 inches, 30 inches being the width of the drawing paper usually employed; then roll the paper and place it on the solution. Now, taking hold of it by two corners, draw it out slowly: the paper will unroll by itself. This operation can be done by diffused daylight, but, of course, the paper should be dried in a dark room. It dries rapidly. Endless rolls are prepared by machinery. To expose, the drawing is placed in the printing frame, face downwards, and the sensitive paper laid over it. The whole is then pressed into contact by interposing a cushion between the lid of the frame and the paper, and exposed so that the rays of light fall perpendicularly upon it.
The cyanofer preparation is quite sensitive. From half a minute to two minutes exposure, according to the intensity of the light and the thickness of the coating, is sufficient in sunshine to reproduce a drawing made on the ordinary tracing paper. In the shade, by a clear sky, the exposure is about [pg 39] five times longer, and varies from half an hour to an hour and more in cloudy weather, but then the design is seldom perfectly sharp.
The progresses of the impression is followed by opening one side of the printing frame and examining the proof. The exposure is sufficient when the paper is tinged brown on the parts corresponding to the ground of the design. The image appears then negative, that is, yellowish on a tinged ground.
Another and more safe method of ascertaining the correct time of exposure, which can be employed concurrently with the other, is to place a few strips of the same sheet of sensitive paper between the margin of the design, upon which a few lines have been traced, and the paper, and, without opening the frame, to draw one of them, from time to time, and dip it in the developing solution. If the whole strip be tinted blue, the proof is not sufficiently exposed; but if the lines soon appear with an intense coloration on the yellowish ground of the paper, and the latter do not turn blue in a minute, at the most, the exposure is right. By excess, the lines are with difficulty developed or broken.
For developing, we provide with three wooden trays lined with lead or gutta-percha, or, more economically, coated with yellow wax. The wax is melted, then applied very hot, and, when it is solidified and quite cold, the coating is equalized with a hot iron, whereby the cracks produced by the contraction of the wax when cooling are filled up.
One of these trays should contain a layer, about three-quarters of an inch thick, of an almost saturated solution of potassium ferrocyanate (the developer); the next be filled with water, and the third with water acidified by sulphuric acid in the proportion of three per cent. in volumes.
All this being ready, the margin of the proof is turned upwards—so as to form a disk of which the outside is the impressed surface—in order that the ferrocyanate solution does not find its way on the back of the proof, which would produce stains. Now the proof is laid, the lower edge first, on the developer, and gradually lowered upon it, when, taking immediately hold of it by the two corners nearest to the body, [pg 40] it is lifted out and held upright to allow one following the development of the image; and, presently, if any air-bubbles are seen on the proof, they should at once be touched up with a brush wetted with the ferrocyanate solution; the reason explains itself.
The image appears at once. As soon as the fine lines are well defined, the blue intense, and, especially, when the ground has a tendency to be tinged blue, the proof is placed in the tray filled with water and in this turned over two or three times, when it is immersed in the diluted sulphuric acid. In this bath the print acquires a deep blue coloration, consisting of Prussian blue, and the ground becomes tinted with a blue precipitate without adherence, which is easily washed off by throwing the liquid on the proof with a wooden spatula, or, better, by rubbing with a rag tied to a stick. When the ground is cleared, and after three or four minutes immersion to dissolve the iron salts acted on, the proof is rinsed in water several times renewed to free it from acid, and hung to dry.
There are two causes of failures in this process, viz., over and under-exposure. In the former case the fine lines are broken or washed out in clearing the proof (which may also arise from the drawing made with an ink not opaque enough); in the latter the ground is more or less stained.
The blue stains, the lines for corrections, etc., are erased with the the potassic oxalate (blue salving, as it is termed) whose formula has been given.
The additions, corrections and writing are made with a Prussian blue ink prepared by mixing the two following solutions:
| A. | Ferric chloride, dry | 4 parts |
| Water | 350 parts | |
| B. | Potassium ferrocyanate | 15 parts |
| Water | 250 parts |
The precipitate being collected on a filter and washed until the water commences to be tinged blue, is dissolved to the proper consistency in about 400 parts of water. This ink does not corrode steel pens.
It has been stated that the cyanofer process keeps for years [pg 41] if preserved from the combined action of dampness and the air. The writer found in his practice that the ferric salts in presence of the organic matters (the sizes) acts as does potassium bichromate and renders, in a certain period, the cyanofer film insoluble even after a prolonged insulation. Paper freshly prepared is always more sensitive and gives better whites and generally finer results.
The prints can be toned black in operating as in the cyonotype, but the results are seldom good.
Captain Pizzighelli's formula is as follows: Prepare
| A. | Gum arabic | 15 parts |
| Water | 100 parts | |
| B. | Ammonia ferric citrate | 45 parts |
| Water | 100 parts | |
| C. | Ferric chloride | 45 parts |
| Water | 100 parts |
For sensitizing mix in order:
| Solution A | 100 parts |
| Solution B | 40 parts |
| Solution C | 20 parts |
The mixture very much thickens at first, but becomes sufficiently fluid for use in a few hours. It keeps well for two or three days. Leaving out B and replacing it by rain water, this makes also a good solution for the cyanotype.
This process gives black positive impressions on white ground from positive clichÉs, and negative impressions from negative clichÉs. It has been attributed to Mr. Colas, but in reality it was invented by Mr. Poitevin, who describes it as follows in his communication of May, 1860, to the SociÉtÉ Francaise de Photographie:
“I make a solution containing—”
| Iron perchloride, cryst | 10 parts |
| Tartaric acid | 3 parts |
| Water | 100 parts |
“I apply the paper on this mixture and let it dry spontaneously in the dark, and at the moment of using it I completely desiccate it at a gentle heat. Thus prepared the paper is of a deep yellow color. Light decolors it rapidly, and ten or twelve minutes' exposure through a positive clichÉ suffices to well impress it, that is, to reduce in the whites the iron perchloride to the state of protochloride.”
“To print, one is guided by the decoloration of the paper, and even for more facility I add to the solution of iron perchloride and tartaric acid a small quantity of a solution of potassium sulphocyanide for the purpose of obtaining a red tint, which is more visible and disappears also under the influence of light in proportion to the decomposition of the perchloride. One obtains then after exposure a red design on the white ground of the paper. This red color is not permanent. It even disappears by keeping the proof in the dark.”
“To develop and then to fix the design thus obtained I wash rapidly the paper in ordinary water, or better, in water holding chalk in suspension. The red coloration disappears, a part of the iron perchloride is washed out, and in the parts which have not been acted on by light the perchloride is transformed into sesquioxide. I replace then the water by solution of gallic acid or of tannin and the image progressively appears in ink-black. When I judge the image to be sufficiently intense I wash the proof in rain water, in preference to ordinary water, [pg 43] which might cause the gallic acid and tannin to turn brown. I sponge between sheets of blotting paper and let the proof dry spontaneously.”
“If in place of gallic acid I use a diluted solution of potassium ferricyanide (red prussiate of potash), Prussian blue is formed in the parts acted on by light. The preparation is even sensitive enough to permit one to obtain an impression in the camera obscura in developing by the ferricyanide.”
“As to the proofs in gallate (or tannate) of iron, they can be transformed into Prussian blue in a solution of potassium ferrocyanide (yellow prussiate of potash) slightly acidified by sulphuric acid.”
The paper most suitable for this process is that which has been previously well sized with starch, as explained in a special paragraph of this pamphlet. Paper prepared with a film of coagulated albumen gives also good results. It may be prepared by brushing as well as by floating, but in either case the paper should be wetted on the surface only and dried rapidly at a temperature of about 115 deg. Fahr. (46 deg. C.) and kept in a dry place. It does not keep for more than from ten to fifteen days, owing to the hygroscopicity of the iron compound. Mr. Colas, who prepares the paper for the Parisian market, I think, states that he avoids its deterioration by keeping it wrapped in blotting paper, between two sheets of India rubber, to exclude air and dampness. Silvered albumen and plain paper, well desiccated, could be kept in that way for a certain period, especially if the blotting paper is impregnated with sodium bicarbonate and well dried.
Mr. A. Fisch advises to discard the preliminary washing and to develop just on the removal of the proofs from the printing frame. In operating in this manner the development is best made by floating, taking care that the solution does not run off the back of the proof.
The developer may consist of a dilute solution of nutgalls or of
| Tannin or gallic acid | 4 parts |
| Oxalic acid | 0.15 parts |
| Water | 1,000 parts |
After developing the proof should be washed rapidly—under a jet of water, if possible—for were the iron salt and the [pg 44] reagent not soon removed, or any remain in the paper, the ground would be tinted violet. And whatever be the care taken, it very seldom occurs that the whites are pure when the proof is dry. This for half-tone pictures has not a great importance, but for the reproductions of plans it is sometimes objectionable. In fact it must be acknowledged that none of the processes now at our disposal—if we except the so-called Artigues process described further on—gives an entirely satisfactory result. A simple and expeditious process, yielding intense black impressions on a white ground, is yet to be found for the reproduction of plans, maps, etc., without resorting to a negative clichÉ or drawing.
This process gives positive impressions from negative clichÉs.
| Uranic nitrate | 10 parts |
| Cupric nitrate | 2 parts |
| Water | 100 parts |
Float for a minute strong, well-sized paper on this solution and let it dry spontaneously in the dark. Expose until the image is visible, then develop by floating on a solution of potassium ferricyanide at 5 per 100 of water—the image appears at once with a rich brown color. When developed, wash it in several changes of water until the unaltered salts are eliminated. The proof is then fixed, and, if too intense, can be reduced in water slightly acidified with hydrochloric acid. A fine black image is obtained by toning in a solution of platinic chloride at 1 per 100 of water.
The chemical actions giving rise to the formation of the metallic ferrocyanide, of which the image consists, are quite complicated. Under the luminous agency the uranic nitrate is first reduced, then the uranous oxide acts on the cupric nitrate, forming cupric oxide, which is finally reduced to the metallic state. This metal now converts the ferricyanate in the ferro compound, which, by another action, forms both cupric and uranic ferrocyanate.
The following uranium process gives black impressions:
In a saturated solution of tartaric acid dissolve freshly precipitated ferric oxide, and keep the solution—ferric tartrate—in the dark. To prepare the sensitizing solution, dissolve 20 parts of uranic nitrate and from 1 to 3 parts of tartaric acid in 100 parts of water, and add a small quantity of ferric tartrate, the proportion varying with the tint desired: an excess gives a blue black. With this solution brush the [pg 46] paper over, and, when dry, expose under the negative clichÉ, then develop with a solution of potassium ferricyanate at 4 per 100 of water. To fix, it suffices to wash in water, renewed three or four times.
As pointed out by Mr. B. J. Burnett (see Introduction), many photographic processes can be devised by basing them upon the various chemical changes, of which uranous oxide, reduced by light from the uranic nitrate or sulphate, is susceptible by means of metallic or organic reagents.
In the Appendix some of the most important processes, with or without silver salts as reagents, will be described.
The aniline process was published in 1865, by Mr. Willis, the inventor of the platinotype.
There are various methods of operating; we will briefly describe them.
| SENSITISING SOLUTION. | ||
|---|---|---|
| 1. | Potassium bichromate | 6 parts |
| Sulphuric acid | 6 parts | |
| Magnesium chloride | 10 parts | |
| Water | 150 parts | |
Willis recommended 10 parts of solid phosphoric acid instead of sulphuric acid; the latter forms a preparation about twice more rapidly reduced.
| 2. | Potassium bichromate | 10 parts |
| Manganous sulphate | 4 parts | |
| Potassium bisulphate | 20 parts | |
| Water | 300 parts | |
| 3. | Ammonium bichromate | 5 parts |
| Ammonium chloride | 5 parts | |
| Cupric sulphate | 1 part | |
| Sulphuric acid | 8 parts | |
| Water | 150 parts |
Good well-sized paper should be employed. Rives is too tender and absorbs too much. Steinbach is better. For small sizes, whatever be the paper selected, it is well to size it with starch and, if possible, to calender it on a hot steel plate, or, in lieu, to iron it. This is not, however, a sine qua non. [pg 48] The paper is sensitized by brushing or by floating. To sensitize by floating, it should be left but for a few seconds on the solution and removed by dragging it on a glass rod in order to remove the superfluous liquid. Only the surface of the paper should be impregnated, otherwise the whites would be more or less tinted and the image imbedded not as sharp.
Sensitized, the paper must be dried as rapidly as possible. It does not keep, and should be employed the day it is prepared or the day after, keeping it well wrapped in paper.
As said above, it is exposed under a positive clichÉ, plans, designs, etc., drawn on tracing paper or linen. The more transparent the material, the more rapid the chemical changes. During the insolation—and it is very short—the chromic compound is reduced, the parts corresponding to the ground, that is, the transparent parts of the clichÉ, are discolored, while those under the design remain unaltered; the image being, therefore, faintly visible, and being formed of the chromic mixture, it is developed by the fumes of aniline in a blue black tone. Therefore, if the paper be not sufficiently exposed, the ground is colored like the image, although not as deeply, since the dye formed is proportionate to the more or less quantity of unreduced compound, and if exposed too long the image is imperfectly developed or not at all by excess.
The discoloration of the ground, which turns to a greenish hue, easily indicates when the exposure is sufficient. But, to ascertain it, the beginner should use tests as in the cyanofer process. Mr. Endemann regulates the time of exposure by partly covering a strip of the sensitive paper with a piece of the tracing material upon which the design is made, and exposing the whole until the covered part of the paper assumes the same shade as the part directly exposed to light.
To develop the print is placed in the bottom of a tray, which is then covered with a lid upon which is pinned blotting paper well imbued with an aniline and benzine mixture, or the reverse; that is, exposing the print fastened to the lid and placing the aniline on the bottom of the tray. The tray should be hermetically closed; that is a condition to obtain a fine and equal coloration. For this purpose the lid should be [pg 49] well lined with sheets of blotting paper and a weight placed over it during the operation. Large prints are necessarily developed in a fumigating box made ad hoc. The aniline solution consists of
| Aniline (commercial for red) | 8 parts |
| Benzine, rectified | 100 parts |
In place of benzine, ether U.S.P., sp. grav. 0.837, may be used.
When the proof is not over-exposed the development commences in a few minutes. The image first takes a dirty black olive color which turns blue in water, then the tone darkens to a dark-brownish tint. The time of exposure to the aniline fumes depends on the time of insolation; if short, the ground is soon tinted, and consequently the development should then be stopped; if over-exposed, the development proceeds slowly. The darkest tone is obtained by a rather full exposure which admits a long fumigation. Sometimes the image takes a green color; it suffices then to wash the proof in water rendered alkaline by a few drops of aqueous ammonia to obtain the normal color.
To somewhat improve the tone of the image and, if objectionable, to remove the chromic oxide which tinges the ground greenish, the proof should be immersed in a dilute solution of sulphuric acid 1:100, then washed twice, and finally passed in ammoniacal water 1:100.
Mr. Hermann Endemann has published, in 1866, the following process in the Journal of the American Chemical Society, pp. 189 et seq.:
The paper, which must be well sized with glue, 1:50, is sensitized with the following solution and exposed when dry, but still slightly damp:
| A. | Potassium bicarbonate | 1 ounce or 480 parts |
| Salt | 1 ounce or 480 parts | |
| Sodium vanadate | 2/3 grain or 0.66 part | |
| Water | 20 ounces or 9,600 parts | |
| B. | Sulphuric acid | 2 ounces or 960 parts |
| Water | 10 ounces or 4,800 parts |
When cold mix to A.
[pg 50]“From the composition of the solution,” says Mr. Endemann, “it is evident that it must be strongly acid; but when this solution is exposed to light, in the presence of the organic substances of the paper, the acidity of the solution disappears, we obtain potassium and sodium sulphates, basic chromium sulphate, salt and vanadic acid. While, therefore, the unchanged parts of the paper remain acid, the changed parts acquire a neutral reaction, and while the first will readily assimilate bases, the second will not. Exposed in an atmosphere laden with water and aniline, the aniline will be absorbed in those parts where the solution remains acid and in proportion to the remaining acidity.”
To develop the image the paper is spread over the opening of a frame tightly placed on a pan, in the bottom of which is heated a solution of aniline in water, 1:50, until the image appears brown, and for further development in a box laden with steam water, which, according to Mr. Endemann, requires two hours to obtain a deep black coloration. To remove the chromium compound the picture is immersed in a solution of aqueous ammonia, 1:6, then washed and dried.
A few years ago the aniline process was improved by developing the image with the aniline-benzine mixture vaporized by steam in a box made specially for that purpose, whereby a reproduction can be obtained in less than ten minutes.
In the photographic department of Messrs Poulson & Eger's Hecia Architectural and Ornamental Iron Works, which is directed by Charles Bilordeaux, this process is worked in the following manner:
The developing is made of sheet iron with a door sliding up and down, it being balanced by a counterpoise, and provided with a chimney. In the box is a gutter, extending the whole length of the bottom, covered with muslin and connected to a steam pipe; there is also a coil similarly connected. After the insolation, which requires about one minute in sunshine, the print is suspended in the box, the muslin brushed over with the solution of aniline, and live steam allowed to pass through the gutter for only two minutes, whereby the aniline being vaporized acts on the chromic salt and develops the image; then the steam is allowed in the coil, and, in from three to four [pg 51] minutes, the paper is dry and the picture finished. The image stands on a slightly greenish ground, which is not objectionable for the purpose the reproductions are made.
The sensitizing solution is similar to that published by Mr. Endemann, viz.:
| Potassium bichromate | 460 grams |
| Sodium chloride | 460 grams |
| Ammonium vanadate | 0.75 gram |
| Sulphuric acid | 1 liter |
| Water | 13 liters |
Primuline, discovered in 1887 by Mr. A. G. Green, an English chemist, is a dye of a primrose color, possessing a great affinity for cotton fibers, to which it is readily fixed by simply immersing the material for a few moments in a hot solution of the dye. If the material so dyed be placed in an acidified solution of nitrous oxide, the primuline is diazotized, forming a derivative compound of a deeper color, which fades in the light, and which in presence of amines and phenols gives rise to a variety of dyes whose color depends on the reagent employed, while, when acted on by light, the resulting compound is entirely deprived of this property. In other words, the diazotized primuline acts as a mordant only when not altered by the luminous action.
The chemical change light effects in the diazotized primuline is not well known. It is pretty certain, however, that nitrogen is set free, for if gelatine imbued with primuline be immersed in water after insulation, nitrogen is set free and can be collected as usual in a tub filled with water and inverted on the substance.
By itself diazotized primuline is slowly influenced by light, but quickly acted on in presence of organic substances. It is more sensitive when applied on cotton or paper than on wool, silk, linen, and such organic compounds as gelatine, albumen, caseine, starch, etc. Its sensitiveness is about one-tenth less with gelatine than with cotton.
The sensitiveness of diazotized primuline to light, when united to organic substances and the different colors which can be obtained with the unaltered compound, have given rise to an interesting printing method, the invention of Messrs. A. G. Green, C. F. Cross, and E. J. Bevan, which yields positive impressions from positive clichÉs. The manipulations of the process are simple:
In a certain quantity of rain water, kept at nearly the boiling [pg 53] temperature by an alcohol lamp placed under the vessel, dissolve per cent. 2 parts of commercial primuline, and in this immerse, by means of a glass rod, some pieces of calico—free from dressing—turning them over several times during the immersion. When the fibers are well imbued, which requires from four to five minutes, remove the calico with the glass rod and rinse it thoroughly in water. This done, wring out the superfluous liquid as much as possible, and, finally, immerse each piece separately in a solution of
| Sodium nitrite, commercial | 7 parts |
| Hydrochloric acid, commercial | 16 parts |
| Water | 100 parts |
After turning the pieces of calico two or three times over, they are rinsed to eliminate the acid, then drained and placed between sheets of blotting paper to dry. All this, except the impregnation with primuline, should be done in the dark room.
As said above, primuline is transformed by nitrous oxide into a diazotized compound, and consequently the material is now susceptible of being acted on by light. It does not keep, and should be exposed, etc., soon after its preparation.
Paper is impregnated with primuline either by floating or brushing. The best results are obtained with paper previously sized with arrowroot or gelatine in order to keep the image entirely on the surface of the paper.
Linen, silk and wool are treated as calico.
The clichÉs should be positive to obtain positive expressions and somewhat more opaque than those employed in the processes before described, else vigor and intensity could not be obtained. Here we must state that the primuline process seems to be better adapted for the reproductions of drawings, such as made for the black process, and of opaque photo-clichÉs in lines, or white and black, than for printing in half tone.
When the material to print upon is thick and wholly impregnated with diazotized primuline, it is advisable, since the insulation could not be prolonged to effect the change through, to expose the back of the material for a certain but [pg 54] short period in order to clear it. This is especially advantageous when the clichÉ is not of good intensity.
During the exposure, which varies from 30 seconds to 10 minutes and more by a dull light, the progresses of the luminous action is seen by the bleaching of the material which assumes a dingy coloration. But in order to ascertain when the decomposition is complete on the ground of the image, it is well to use tests as in the cyanofer process, dipping one of them in the developer from time to time.
The developers are compounded as follows:
| FOR RED. | |
|---|---|
| Beta-naphthol | 4 parts |
| Caustic potassa | 6 parts |
| Water | 500 parts |
Rub the alkali and the naphthol with a little water in a mortar and add the remainder of the water.
| FOR ORANGE. | |
|---|---|
| Resorcin | 3 parts |
| Water | 500 parts |
When dissolved add
| Caustic potassa | 5 parts |
| FOR YELLOW. | |
|---|---|
| Carbolic acid, cryst | 5 parts |
| Water | 500 parts |
| FOR PURPLE. | |
|---|---|
| Naphthylamine | 6 parts |
| Hydrochloric acid, in volume | 6 parts |
Mix in a mortar, then add
| Water | 500 parts |
| FOR BLACK. | |
|---|---|
| Eikonogen, white crystals | 6 parts |
| Water | 500 parts |
Pulverize the eikonogen, add the water and, at the same time, the material on its removal from the printing frame, and keep in motion until the development is effected.
| FOR BROWN. | |
|---|---|
| Pyrogallol | 5 parts |
| Water | 500 parts |
After the development, which requires but a few moments, it suffices to wash the material to fix the image by eliminating the soluble compounds. However, for purple the material should be passed in a dilute solution of tartaric acid and not washed afterwards; it should remain acid.
When it is desirable to obtain an impression in several colors, the various developers are thickened with starch, then locally applied with a brush on the image, which is always visible after exposure.
For printing on wood, glass and porcelain, see further on.
Printing on Wood.—To print on a wood block a design to be engraved on the same presents certain difficulties. In the first place, the sensitizing solution must not be absorbed by the wood, but remain wholly on its surface; then the photo film, although thick enough to produce an image sufficiently intense to be distinctly visible in all its details, should not scale or clip away under the graver, and not interfere in any way with the work of the artist; the least touch of the graver must reach the wood and make its impression. Lastly, the design should be permanent. These difficulties will be avoided by adhering to the instructions given in the lines following.
The solution to render impervious the surface of the wood consists of
| Common gelatine | 5 parts |
| Gum arabic | 3 parts |
| Castile soap | 3 parts |
| Water | 100 parts |
Dissolve by heat on a water bath.
To apply it, the wood is rubbed with fine sandpaper, then heated over a spirit lamp to about 86 deg. Fahr. (30 deg. C.) and upon it is poured in excess the liquefied and quite warm solution, which must be allowed to penetrate in the pores of the wood by letting it gelatinize, when it is wiped off clean. Nothing must remain on the surface of the wood. This done, and while still damp, the preparation is rendered insoluble by pouring over a solution of alum at 5 [pg 56] per 100 of water. The object of this preliminary operation is to render the wood impervious, and therefore to prevent the sensitizing solution to penetrate its texture. The wood is then heated again and its surface whitened with a little silver white or sulphate of barium, diffused in a small quantity of the following warm solution:
| Gelatine | 1 parts |
| Alum | 0.1 part |
| Water | 100 parts |
While wet, this is smoothed with a jeweler's brush, taking care to leave on the wood, a very thin layer of the mixture, only sufficient to obtain a white surface which, by contrasting with color of the wood assists the engraver in his work. The wood should now be allowed to dry thoroughly, when it is coated with a tepid solution of
| Isinglass | 3 parts |
| Water | 100 parts |
and dried.
Now the sensitizing process differs according as whether the clichÉ is positive or negative. In the former case the preparation is sensitized with the solution employed in the black process, proceeding afterwards as usual; in the latter, that is, when the clichÉ is negative, the best process is the cuprotype.
For printing, special frames are employed to permit one to examine the progress of the impression from time to time without the possibility of either the wood block or the clichÉ moving. These frames open in two. The upper frame is provided with screws on the four sides to hold firmly the block when it is placed into contact with the clichÉ by means of the screws fixed on the cross bars. As to the clichÉ, if it is made on a glass plate, it is secured on the thick glass plate of the lower frame by two wooden bars against it pushed by screws.
[pg 57]When the block is ready for printing, the prepared side is usually concave. It is straightened by slightly wetting the back and resting it on one end, prepared side against the wall.
Printing on Canvas.—The canvas should be first brushed with a solution of aqueous ammonia in alcohol, 1:3, to remove greasiness until the thread just commences to show, then, when rinsed and dry, rubbed with fine sand to give a tooth, dusted, washed with a sponge and then coated with the following solution, proceeding afterwards as in the cuprotype process:
| Isinglass | 8 parts |
| Uranic nitrate | 5 parts |
| Copper nitrate | 2 parts |
| Water | 200 parts |
Printing on Opal, Celluloid, etc., is quite simple; it suffices to coat the material with the following gelatine solution, and, when the film is dry, to proceed in operating by any one of the processes before described.
The sensitizing compound may be incorporated to the gelatine solution, but we prefer not to do it and to sensitize the plates as they are wanted for use.
| A. | Gelatine | 4 parts |
| Water | 70 parts in volume |
Dissolve and mix little by little in order:
| B. | Chrome alum | 0.25 parts |
| Water, hot | 20 parts | |
| C. | Alcohol | 10 parts |
When coated place the plates on a level stand until the gelatine is set, and let them dry on a rack.
Transparencies.—Prepare the plate as directed above with
| A. | Gelatine | 6 parts |
| Water | 70 parts | |
| B. | Chrome alum | 0.3 part |
| Water, hot | 20 parts | |
| C. | Alcohol | 10 parts |
Sensitize with the uranic-copper solution employed in the cuprotype. By this process transparencies of a rich brown, [pg 58] not actinic, color are obtained. Consequently they can be used to reproduce negatives by the same process. For lantern slides they may be toned black by platinic chloride.
To strip off the picture, apply, first, on the glass plate a substratum of India rubber, 2 to 100 of benzole, coat with plain collodion, immerse the plate in water as soon as the film is set, and when greasiness has disappeared pour on the gelatine solution and proceed.
For tranferring on any material, a sheet of paper is immersed in a solution of India rubber cement in 20 parts of benzole, dried, coated with the gelatine solution, sensitized, etc., by operating in the ordinary manner. After development, the proof, being dry, is brushed over with alumed gelatine moderately warm, dried, immersed in tepid water until the gelatine is softened and tacky, when it is placed on the material and squeezed into contact. This done, the transfer should be allowed to dry thoroughly. Now, by imbuing the proof with benzole to dissolve the India rubber, the paper is easily stripped off, leaving behind the picture adhering to the material.
[pg 59]We call the attention of metal engravers to this process. It is well known that wood engravers have their original designs photographed on the block in order to save considerable time by not making the drawing themselves; moreover the cost is nominal, so to say, and the copy more true and perfect than it can be done by hand. Why should not the copper engraver and the aquafortist avail themselves of the same advantages? A few do it secretly, no doubt, but the generality not knowing the process, or, if so, not having tried it, think it is not possible or that it may spoil their plates. This is an error. It can be done and very easily by adhering to the following instructions:
Dissolve 2 parts of ammonium bichromate in 100 parts of water, and in this let soak for an hour or so 10 parts of Coignet's best gelatine, then dissolve on a water bath, filter through flannel, and the solution is ready for use.
Before being coated, the plate should necessarily be cleaned free from oxidation and greasy matters. This is done by immersing the plate for a few moments in a warm solution of common potash, then rinsing and rubbing it with chalk moistened with a little water, when after rinsing again and draining the plate should be immediately prepared.
To spread the gelatine solution in an even and thin layer, a tournette is employed. The most simple consists of a round wooden stick of which the upper part is carved in the form of a cup with an edge, or rim, about one quarter of an inch broad. On this rim is melted some gutta-percha, upon which the plate is pressed into contact and adhers quite firmly when the gutta-percha is solidified. The stick is perforated at the lower end and revolves on an iron pivot fixed at the bottom of the support, being held in the opening on the platform of the same, as shown in the diagram on the following page.
The plate being fastened to the tournette, the warm gelatine solution is flowed over it and spread to the edges by means of [pg 60] a glass rod or a piece of cardboard, avoiding air bubbles. This done the tournette is set into motion, and when the film is equalized, which is done in a moment, the plate is detached, placed on a leveled stand and slowly dried with the spirit lamp.
By a good light the exposure on the shade does not exceed twenty minutes with a pretty intense transparency, and should be regulated with a photometer. When the insulation is sufficient, the image is slightly visible, and should be so. The plate is then bordered with banking wax and bitten-in with a solution of ferric chloride at 45 deg. BaumÉ, or—
| Ferric chloride, crystal | 20 parts |
| Hydrochloric acid | 1 part |
| Water | 100 parts |
The parts of the gelatine film the most acted on are impermeable, so to say, and consequently do not allow the etching fluid to penetrate to the copper; while those the least impressed are permeated according as to their degree of insolation, Therefore, when the ferric chloride solution is poured upon the film and carefelly brushed over with a soft brush, in a few moments the image progressively appears, the deep blacks first, then the half tints, and lastly the most delicate details, the whole requiring but a few minutes. It is now that the etching [pg 61] action should be stopped by washing under the tap. However, should by excess of exposure, or any other cause, the details not appear within five or six minutes, the ferric chloride should nevertheless be washed off, for then it may find its way under the film and the plate would be spoiled. After washing the gelatine is dissolved in a solution of potash, etc., when the image would be found slightly engraved.
Should the image be in half-tints, it would be advisable to apply a grain of rosin on the gelatine film just before etching. To engrave on steel the operations are the same, but on its removal from the printing frame the plate should be soaked with water renewed several times until the bichromate is washed off. The film is then dried spontaneously and afterwards flowed for about two minutes with the Solution A, then, this being thrown away, with the Solution B, which is allowed to act for a similar period.
| A. | Nitric acid, pure | 120 parts |
| Silver nitrate | 6 parts | |
| Alcohol, 95 deg | 50 parts | |
| Water | 75 parts | |
| B. | Nitric acid, pure | 5 parts |
| Alcohol, 95 deg | 40 parts | |
| Water | 60 parts |
This process consists in converting a clichÉ in half tones into one in lines, which can be directly printed on paper, or impressed, by means of an ink transfer made as explained before, on a stone, or on a zinc or copper plate for etching in relief, or in intaglio, according as the clichÉ is negative or positive.
A clichÉ on gelatine, but preferably on a collodion film, is varnished with a solution of yellow wax and bitumen in benzole and turpentine-oil:
| Bitumen of Judaea | 8 parts |
| Yellow wax | 2 parts |
| Benzole | 40 parts |
| Turpentine oil | 60 parts (filter) |
then etched as done to engrave in the aquafortis manner, the corrections being made by applying with a brush some of the above varnish on the defective parts, which are worked over when the varnish is dry.
The tools are simply needles of various thickness ground in sharp square and round points of different sizes.
When the etching is finished, the parts which should form the ground, or white parts of the design, being covered with the bitumen varnish is non-actinic, or, in other words, does not admit the light acting on the sensitive plate preparation employed to reproduce the design, except by an exposure a good deal longer than that necessary to reduce the metallic salts.
The engraver will see at once that, although it greatly simplifies the copying work and, consequently, saves much time, this process does not, however, bind him to any rules and leaves him perfectly free to follow its inspirations and make such alterations as he thinks proper to produce artistic effects; in a word, the reproduction will no more be a picture taken [pg 63] by a mechanical process, so to say, but an original drawing reflecting his talent and characteristic manner.
A similar process much employed by photo engravers, and presenting the same advantages, is to convert an ordinary photograph on paper—or a blue print, as devised by the writer—into a design in lines by drawing with India ink, or the special ink of Higgins, and, this done, to wash off the photographic image, the design being afterwards reproduced by the ordinary processes as a negative or a positive clichÉ.
When the photograph is a silver print especially made for the purpose in question and, consequently not toned, but simply fixed in a new thiosulphate (hyposulphite) bath, and well washed—it is bleached by flowing over a solution of—
| Bichloride of mercury | 5 parts |
| Alcohol | 40 parts |
| Water | 100 parts |
If the photograph has been toned, i.e., colored by a deposit of gold, or if it was fixed in a thiosulphate bath in which toned prints have been fixed, then the image is dissolved by treatment in a solution of potassium cyanide in alcoholized water.
When a blue photograph is reduced, it is advisable before drawing upon it to first reduce its intensity by a prolonged immersion into water. Pale blue is a very actinic color which is not reproduced in photography, except by the ortho-chromatic process, or if it does, the impression being very weak, is not objectionable. When the image has not been sufficiently or not at all bleached, the blue is dissolved by an alcoholized solution of the blue solving.
[pg 70]This process, devised by J. Wothly, in 1864, did not receive from the photographers the attention it merits, as it is always the case when a process is patented, and can be replaced by another equally practical which is not. It gives pictures of a very good tone, which are quite permanent; we have some made in 1866, which are suffered no change whatever, they seem to have been printed from yesterday.
The first process given by Wothly does not appear to be complete. It has been well described by H. Cooper and a gentleman who signs by the initial letter X.
The process published in 1865 by Wothly is as follows: A sheet of paper is sized by brushing with a paste made of 24 parts of arrowroot in 500 parts of water, to which are added a few drops of a solution of citric or tartaric acid, then coated with a collodion consisting of 100 cubic centimeters of plain collodion, a few drops of oil of turpentine and 30 cubic centimeters of the following sensitizing solution:
| Nitrate of uranium | 30 to 90 parts |
| Chloride of platinum | 2 parts |
| Alcohol | 180 parts |
The time of exposure is about that required for paper prepared with silver chloride. The image is bluish-black but weak. After washing the print is immersed in a solution containing 0.5 parts of chloride of gold for 2,000 parts of distilled water, and then fixed in a bath of sulphocyanate of potassium, which tones the image blue-black.
It may happen that the proof is slightly tinted red. This arises from a small quantity of lime in the paper which forms uranate of calcium.
To prevent the proofs turning yellow, it should be washed in an exceedingly weak solution of acetic acid.
If, after exposure, the print is immersed, without it being [pg 68] washed, in the gold bath, the image becomes rose-red, but the whites remain pure. The effect is peculiar.
