THE CYANOFER. (Pellet's Process.)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 quality50 partsWater170 partsB.Tartaric acid12 partsWater80 partsC.Ferric chloride solution at 45 deg. Baumé35 parts in volumeMix 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 asine qua nonto 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 fallperpendicularlyupon 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 aPrussian blue inkprepared by mixing the two following solutions:A.Ferric chloride, dry4 partsWater350 partsB.Potassium ferrocyanate15 partsWater250 partsThe 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.10The prints can be toned black in operating as in the cyonotype, but the results are seldom good.Captain Pizzighelli's formula is as follows: PrepareA.Gum arabic15 partsWater100 partsB.Ammonia ferric citrate45 partsWater100 partsC.Ferric chloride45 partsWater100 partsFor sensitizing mixin order:Solution A100 partsSolution B40 partsSolution C20 partsThe 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.THE BLACK OR INK PROCESS. (Ferro-tannate Process.)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 theSociété Francaise de Photographie:“I make a solution containing—”Iron perchloride, cryst10 partsTartaric acid3 partsWater100 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 ofTannin or gallic acid4 partsOxalic acid0.15 partsWater1,000 partsAfter 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.THE CUPROTYPE. (Burnett's Process.)This process gives positive impressions from negative clichés.Uranic nitrate10 partsCupric nitrate2 partsWater100 partsFloat 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.The aniline process was published in 1865, by Mr. Willis, the inventor of the platinotype.11It is based on the oxidation of aniline by chromic acid, thus: A sheet of paper brushed with a solution of potassium bichromate and sulphuric acid, dried, and after insolation under a cliché exposed to the fumes of aniline which, in reacting with the chromic compound not reduced by light, forms a blue-black image.The process gives, consequently, a positive impression from a positive cliché.There are various methods of operating; we will briefly describe them.SENSITISING SOLUTION.1.Potassium bichromate6 partsSulphuric acid6 partsMagnesium chloride10 partsWater150 partsWillis recommended 10 parts of solid phosphoric acid instead of sulphuric acid; the latter forms a preparation about twice more rapidly reduced.2.Potassium bichromate10 partsManganous sulphate4 partsPotassium bisulphate20 partsWater300 parts3.Ammonium bichromate5 partsAmmonium chloride5 partsCupric sulphate1 partSulphuric acid8 partsWater150 partsGood 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, asine 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 usetestsas 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 madead hoc.The aniline solution consists ofAniline (commercial for red)8 partsBenzine, rectified100 partsIn 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 theJournal of the American Chemical Society, pp. 189et 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 bicarbonate1 ounce or 480 partsSalt1 ounce or 480 partsSodium vanadate2/3 grain or 0.66 partWater20 ounces or 9,600 partsB.Sulphuric acid2 ounces or 960 partsWater10 ounces or 4,800 partsWhen 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 bichromate460 gramsSodium chloride460 gramsAmmonium vanadate0.75 gramSulphuric acid1 literWater13 liters[pg 52]THE PRIMULINE OR DIAZOTYPE PROCESS.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 yieldspositive 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 ofSodium nitrite, commercial7 partsHydrochloric acid, commercial16 partsWater100 partsAfter 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 toclearit. 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 usetestsas in the cyanofer process, dipping one of them in the developer from time to time.The developers are compounded as follows:FOR RED.Beta-naphthol4 partsCaustic potassa6 partsWater500 partsRub the alkali and the naphthol with a little water in a mortar and add the remainder of the water.FOR ORANGE.Resorcin3 partsWater500 partsWhen dissolved addCaustic potassa5 partsFOR YELLOW.Carbolic acid, cryst5 partsWater500 partsFOR PURPLE.Naphthylamine6 partsHydrochloric acid, in volume6 partsMix in a mortar, then addWater500 partsFOR BLACK.Eikonogen, white crystals6 partsWater500 partsPulverize 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.Pyrogallol5 partsWater500 parts[pg 55]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, CANVAS, OPAL, AND TRANSPARENCIESPrinting 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 ofCommon gelatine5 partsGum arabic3 partsCastile soap3 partsWater100 partsDissolve 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:Gelatine1 partsAlum0.1 partWater100 partsWhile 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 ofIsinglass3 partsWater100 partsand 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.12For 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:Isinglass8 partsUranic nitrate5 partsCopper nitrate2 partsWater200 partsPrinting 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.Gelatine4 partsWater70 parts in volumeDissolve and mix little by little in order:B.Chrome alum0.25 partsWater, hot20 partsC.Alcohol10 partsWhen 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 withA.Gelatine6 partsWater70 partsB.Chrome alum0.3 partWater, hot20 partsC.Alcohol10 partsSensitize 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]
THE CYANOFER. (Pellet's Process.)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 quality50 partsWater170 partsB.Tartaric acid12 partsWater80 partsC.Ferric chloride solution at 45 deg. Baumé35 parts in volumeMix 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 asine qua nonto 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 fallperpendicularlyupon 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 aPrussian blue inkprepared by mixing the two following solutions:A.Ferric chloride, dry4 partsWater350 partsB.Potassium ferrocyanate15 partsWater250 partsThe 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.10The prints can be toned black in operating as in the cyonotype, but the results are seldom good.Captain Pizzighelli's formula is as follows: PrepareA.Gum arabic15 partsWater100 partsB.Ammonia ferric citrate45 partsWater100 partsC.Ferric chloride45 partsWater100 partsFor sensitizing mixin order:Solution A100 partsSolution B40 partsSolution C20 partsThe 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.THE BLACK OR INK PROCESS. (Ferro-tannate Process.)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 theSociété Francaise de Photographie:“I make a solution containing—”Iron perchloride, cryst10 partsTartaric acid3 partsWater100 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 ofTannin or gallic acid4 partsOxalic acid0.15 partsWater1,000 partsAfter 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.THE CUPROTYPE. (Burnett's Process.)This process gives positive impressions from negative clichés.Uranic nitrate10 partsCupric nitrate2 partsWater100 partsFloat 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.The aniline process was published in 1865, by Mr. Willis, the inventor of the platinotype.11It is based on the oxidation of aniline by chromic acid, thus: A sheet of paper brushed with a solution of potassium bichromate and sulphuric acid, dried, and after insolation under a cliché exposed to the fumes of aniline which, in reacting with the chromic compound not reduced by light, forms a blue-black image.The process gives, consequently, a positive impression from a positive cliché.There are various methods of operating; we will briefly describe them.SENSITISING SOLUTION.1.Potassium bichromate6 partsSulphuric acid6 partsMagnesium chloride10 partsWater150 partsWillis recommended 10 parts of solid phosphoric acid instead of sulphuric acid; the latter forms a preparation about twice more rapidly reduced.2.Potassium bichromate10 partsManganous sulphate4 partsPotassium bisulphate20 partsWater300 parts3.Ammonium bichromate5 partsAmmonium chloride5 partsCupric sulphate1 partSulphuric acid8 partsWater150 partsGood 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, asine 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 usetestsas 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 madead hoc.The aniline solution consists ofAniline (commercial for red)8 partsBenzine, rectified100 partsIn 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 theJournal of the American Chemical Society, pp. 189et 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 bicarbonate1 ounce or 480 partsSalt1 ounce or 480 partsSodium vanadate2/3 grain or 0.66 partWater20 ounces or 9,600 partsB.Sulphuric acid2 ounces or 960 partsWater10 ounces or 4,800 partsWhen 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 bichromate460 gramsSodium chloride460 gramsAmmonium vanadate0.75 gramSulphuric acid1 literWater13 liters[pg 52]THE PRIMULINE OR DIAZOTYPE PROCESS.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 yieldspositive 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 ofSodium nitrite, commercial7 partsHydrochloric acid, commercial16 partsWater100 partsAfter 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 toclearit. 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 usetestsas in the cyanofer process, dipping one of them in the developer from time to time.The developers are compounded as follows:FOR RED.Beta-naphthol4 partsCaustic potassa6 partsWater500 partsRub the alkali and the naphthol with a little water in a mortar and add the remainder of the water.FOR ORANGE.Resorcin3 partsWater500 partsWhen dissolved addCaustic potassa5 partsFOR YELLOW.Carbolic acid, cryst5 partsWater500 partsFOR PURPLE.Naphthylamine6 partsHydrochloric acid, in volume6 partsMix in a mortar, then addWater500 partsFOR BLACK.Eikonogen, white crystals6 partsWater500 partsPulverize 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.Pyrogallol5 partsWater500 parts[pg 55]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, CANVAS, OPAL, AND TRANSPARENCIESPrinting 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 ofCommon gelatine5 partsGum arabic3 partsCastile soap3 partsWater100 partsDissolve 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:Gelatine1 partsAlum0.1 partWater100 partsWhile 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 ofIsinglass3 partsWater100 partsand 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.12For 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:Isinglass8 partsUranic nitrate5 partsCopper nitrate2 partsWater200 partsPrinting 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.Gelatine4 partsWater70 parts in volumeDissolve and mix little by little in order:B.Chrome alum0.25 partsWater, hot20 partsC.Alcohol10 partsWhen 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 withA.Gelatine6 partsWater70 partsB.Chrome alum0.3 partWater, hot20 partsC.Alcohol10 partsSensitize 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]
THE CYANOFER. (Pellet's Process.)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 quality50 partsWater170 partsB.Tartaric acid12 partsWater80 partsC.Ferric chloride solution at 45 deg. Baumé35 parts in volumeMix 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 asine qua nonto 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 fallperpendicularlyupon 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 aPrussian blue inkprepared by mixing the two following solutions:A.Ferric chloride, dry4 partsWater350 partsB.Potassium ferrocyanate15 partsWater250 partsThe 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.10The prints can be toned black in operating as in the cyonotype, but the results are seldom good.Captain Pizzighelli's formula is as follows: PrepareA.Gum arabic15 partsWater100 partsB.Ammonia ferric citrate45 partsWater100 partsC.Ferric chloride45 partsWater100 partsFor sensitizing mixin order:Solution A100 partsSolution B40 partsSolution C20 partsThe 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 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:
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 asine qua nonto 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 fallperpendicularlyupon 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 aPrussian blue inkprepared by mixing the two following solutions:
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.10
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
For sensitizing mixin order:
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.
THE BLACK OR INK PROCESS. (Ferro-tannate Process.)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 theSociété Francaise de Photographie:“I make a solution containing—”Iron perchloride, cryst10 partsTartaric acid3 partsWater100 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 ofTannin or gallic acid4 partsOxalic acid0.15 partsWater1,000 partsAfter 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 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 theSociété Francaise de Photographie:
“I make a solution containing—”
“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
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.
THE CUPROTYPE. (Burnett's Process.)This process gives positive impressions from negative clichés.Uranic nitrate10 partsCupric nitrate2 partsWater100 partsFloat 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.
This process gives positive impressions from negative clichés.
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.The aniline process was published in 1865, by Mr. Willis, the inventor of the platinotype.11It is based on the oxidation of aniline by chromic acid, thus: A sheet of paper brushed with a solution of potassium bichromate and sulphuric acid, dried, and after insolation under a cliché exposed to the fumes of aniline which, in reacting with the chromic compound not reduced by light, forms a blue-black image.The process gives, consequently, a positive impression from a positive cliché.There are various methods of operating; we will briefly describe them.SENSITISING SOLUTION.1.Potassium bichromate6 partsSulphuric acid6 partsMagnesium chloride10 partsWater150 partsWillis recommended 10 parts of solid phosphoric acid instead of sulphuric acid; the latter forms a preparation about twice more rapidly reduced.2.Potassium bichromate10 partsManganous sulphate4 partsPotassium bisulphate20 partsWater300 parts3.Ammonium bichromate5 partsAmmonium chloride5 partsCupric sulphate1 partSulphuric acid8 partsWater150 partsGood 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, asine 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 usetestsas 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 madead hoc.The aniline solution consists ofAniline (commercial for red)8 partsBenzine, rectified100 partsIn 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 theJournal of the American Chemical Society, pp. 189et 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 bicarbonate1 ounce or 480 partsSalt1 ounce or 480 partsSodium vanadate2/3 grain or 0.66 partWater20 ounces or 9,600 partsB.Sulphuric acid2 ounces or 960 partsWater10 ounces or 4,800 partsWhen 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 bichromate460 gramsSodium chloride460 gramsAmmonium vanadate0.75 gramSulphuric acid1 literWater13 liters
The aniline process was published in 1865, by Mr. Willis, the inventor of the platinotype.11It is based on the oxidation of aniline by chromic acid, thus: A sheet of paper brushed with a solution of potassium bichromate and sulphuric acid, dried, and after insolation under a cliché exposed to the fumes of aniline which, in reacting with the chromic compound not reduced by light, forms a blue-black image.The process gives, consequently, a positive impression from a positive cliché.
There are various methods of operating; we will briefly describe them.
Willis recommended 10 parts of solid phosphoric acid instead of sulphuric acid; the latter forms a preparation about twice more rapidly reduced.
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, asine 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 usetestsas 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 madead hoc.The aniline solution consists of
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 theJournal of the American Chemical Society, pp. 189et 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:
When cold mix to A.
“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.:
THE PRIMULINE OR DIAZOTYPE PROCESS.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 yieldspositive 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 ofSodium nitrite, commercial7 partsHydrochloric acid, commercial16 partsWater100 partsAfter 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 toclearit. 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 usetestsas in the cyanofer process, dipping one of them in the developer from time to time.The developers are compounded as follows:FOR RED.Beta-naphthol4 partsCaustic potassa6 partsWater500 partsRub the alkali and the naphthol with a little water in a mortar and add the remainder of the water.FOR ORANGE.Resorcin3 partsWater500 partsWhen dissolved addCaustic potassa5 partsFOR YELLOW.Carbolic acid, cryst5 partsWater500 partsFOR PURPLE.Naphthylamine6 partsHydrochloric acid, in volume6 partsMix in a mortar, then addWater500 partsFOR BLACK.Eikonogen, white crystals6 partsWater500 partsPulverize 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.Pyrogallol5 partsWater500 parts[pg 55]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.
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 yieldspositive 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
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 toclearit. 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 usetestsas in the cyanofer process, dipping one of them in the developer from time to time.
The developers are compounded as follows:
Rub the alkali and the naphthol with a little water in a mortar and add the remainder of the water.
When dissolved add
Mix in a mortar, then add
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.
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, CANVAS, OPAL, AND TRANSPARENCIESPrinting 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 ofCommon gelatine5 partsGum arabic3 partsCastile soap3 partsWater100 partsDissolve 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:Gelatine1 partsAlum0.1 partWater100 partsWhile 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 ofIsinglass3 partsWater100 partsand 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.12For 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:Isinglass8 partsUranic nitrate5 partsCopper nitrate2 partsWater200 partsPrinting 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.Gelatine4 partsWater70 parts in volumeDissolve and mix little by little in order:B.Chrome alum0.25 partsWater, hot20 partsC.Alcohol10 partsWhen 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 withA.Gelatine6 partsWater70 partsB.Chrome alum0.3 partWater, hot20 partsC.Alcohol10 partsSensitize 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]
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
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:
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
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.12
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.
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:
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.
Dissolve and mix little by little in order:
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
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.