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The American Carbon Manual/Swan's Carbon Process

SWAN'S CARBON PROCESS.

Prior to entering into a detailed description of Mr. Swan's Carbon Process, it may be desirable to place before the reader the specification of the patent in which is stated the essential features of principle and practice combined in the process. It proceeds as follows:

“My invention relates to that manner or style of photographic printing known as carbon or pigment printing. In this style of printing, carbon or other coloring matter is fixed by the action of light passing through a negative, and impinging upon a surface composed of gelatine, or other like substance, colored with carbon or other coloring matter, and made sensitive to light by means of bichromate of potash, or bichromate of ammonia, or other chemical substance having like photographic property; those portions of the colored and sensitive gelatinous surface which are protected from the light by the opaque or semi-opaque portions of the negative, being afterwards washed away by means of water, while the parts made insoluble by light remain, and form a print. This kind of photographic printing, although possessing the advantage of permanency, and affording the means of insuring any required tone or color for the print, has not come into general use, because of the difficulties hitherto experienced in obtaining by it delicacy of detail, and complete gradation of light and shade.

“The difficulties referred to were more particularly experienced in attempts to employ paper coated with the colored gelatinous materials, and arose from the fact, that, in order to obtain half-tone, certain portions of the colored coating lying behind or at the back of the photographically-impressed portions required to be washed away, and the employment of paper in the way it has been employed hitherto, not only as a means of supporting the colored coating, but also to form ultimately the basis or groundwork of the print, obstructed the removal of the inner or back portions of the colored coating, and prevented the obtaining of half-tone.

“Now, my invention consists in the formation of tissues adapted to the manner of printing referred to, and composed of, or prepared with, colored gelatinous matter, and so constructed, that while they allow, in the act of printing, free access of light to one surface of the colored gelatinous matter, they also allow free access of water, and the unobstructed removal of the non-affected portions of the colored matter, from the opposite surface, or back, in the act of developing; and I obtain this result either by the disuse of paper altogether, or by the use of it merely as a backing or temporary support of the colored gelatinous matter; the paper, so used, becoming entirely detached from the colored gelatinous matter in the act of developing, and forming no part of the print ultimately.

“My invention consists, furthermore, in the special mode of using the said tissues, whereby superior half-tone and definition in the print are obtained as aforesaid, and also in a mode of transferring the print, after developing, from a temporary to a permanent support, so as to obtain a correction in the position of the print in respect of right and left. In producing the photographic tissues referred to, I form a solution of gelatine, and for the purpose of imparting pliancy to the resultant tissue, I have found it advisable to add to the gelatine solution, sugar or other saccharine matter, or glycerine. To the said gelatinous solution I add carbonaceous or other coloring matter, either in a fine state of division, such as is used in water-color painting, or in the state of a solution or dye, or partly in a fine state of division, and partily in solution.

“With this colored gelatinous solution I form sheets or films, as hereafter described; and I render such sheets or films sensitive to light, either at the time of their formation, by introducing into the gelatinous compound bichromate of ammonia, or other agent of like photographic properties, or by applying to such non-sensitive sheets or films, after their formation, a solution of the bichromate, or other substances of like photographic property. This latter method I adopt when the sheet or film is not required for use immediately after its formation. I will, in my future references to the bichromate of ammonia or the bichromate of potash, or to other chemicals possessing analogous photographic properties, denominate them ‘the sensitizer;’ and in referring to the colored gelatinous solution, I will denominate this mixture ‘the tissue-compound.’ When the tissue to be produced is required for immediate use, I add the sensitizer to the tissue compound; but, where the tissue is required to be preserved for some time before using, I prefer to omit the sensitizer from the tissue-compound, with a view to the tissue being made sensitive to light subsequently, by the application of a solution of the sensitizer.

“With respect to the composition of the tissue-compound, it will be understood by chemists, that it may be varied without materially affecting the result, by the addition or substitution of other organic matters, similarly acted upon by light, when combined with a salt of chromium, such as I have referred to. Such other organic matters are gum arabic, albumen, dextrine; and one or more of these may be employed occasionally to modify the character of the tissue-compound, but I generally prefer to make it as follows: I dissolve, by the aid of heat, two parts of gelatine, in eight parts of water, and to this solution I add one part of sugar, and as much coloring matter in a finely divided state, or in a state of solution, or both, as may be required for the production of a photographic print with a proper gradation of light and shade. The quantity required for this purpose must be regulated by the nature of the coloring matter employed, and also by the character of the negative to be used in the printing operation. Where it is desired that the coloring matter of the print should consist entirely or chiefly of carbon, I prefer to use lampblack finely ground and prepared as for water-color painting, or I use Indian-ink; and where it is desired to modify the black, I add other coloring matter to produce the color desired. For instance, I obtain a purple black by adding to the carbon, indigo and crimson-lake, or I add to the carbon an aniline dye of a suitable color; where the coloring matter used is not a solution or dye, but solid matter in a fine state of division, such as Indian-ink or lampblack, I diffuse such coloring matter through water, or other inert liquid capable of holding it in suspension; and after allowing the coarser particles to subside, I add, of that portion which is held in suspension, as much as is required, to the gelatine solution. In preparing tissue to be used in printing from negatives technically known as ‘weak,’ I increase the proportion of coloring matter relatively to that of the tissue-compound; and I diminish it, for tissue or paper to be used in printing from negatives of an opposite character.

“Having prepared the tissue-compound as before described, I proceed to use it as follows: For preparing sensitive tissue, I add to the tissue-compound more or less of the sensitizer, varying the quantity added, according to the nature of the sensitizer, and to the degree of sensitiveness to be conferred on the tissue to be produced from it. For ordinary purposes, and where the tissue-compound is made according to the formula before given, I add about one part of a saturated solution of bichromate of ammonia to ten parts of the tissue-compound; and I make this addition immediately previous to the preparation of the tissue, and I maintain the tissue-compound in the fluid state, by means of heat, during the preparation of the tissue, avoiding the use of an unnecessary degree of heat; I also filter it through fine muslin or flannel, or other suitable filtering medium, previous to use; and I perform all the operations with the tissue-compound, subsequent to the introduction of the sensitizer, in a place suitably illuminated with yellow or non-actinic light. In forming tissue upon a surface of glass, I first prepare the glass, so as to facilitate the separation of the tissue from it. For this purpose, I apply ox-gall to the surface of the glass (by means of a brush, or by immersion), and allow it to dry. The glass is then ready for coating with the tissue-compound, or I apply to the glass a coating of collodion, previous to the application of the coating of tissue-compound. In this case, the preparation with ox-gall is unnecessary. When collodion is used, the collodion may consist of about ten grains of pyroxyline in one ounce of mixture of equal parts of sulphuric ether and alcohol. I apply the collodion by pouring it on the surface to be coated, and draining off the excess, and I allow the coating of collodion to become dry before applying the coating of tissue-compound. I generally use a plane surface on which to form the tissue, but surfaces of a cylindrical or other form may sometimes be used advantageously. In preparing sheets of sensitive tissue on a plane surface of glass, I prefer to use the kind of glass known as plate, or patent plate. Before applying the sensitive tissue-compound, I set the plate to be coated, so that its upper surface lies in a horizontal position, and I heat the plate to about the same temperature as the tissue-compound, that is, generally, to about 100 degrees, Fahrenheit. The quantity of the tissue-compound that I apply to the glass varies with circumstances, but is generally about two ounces to each square foot of surface coated.

After pouring the requisite quantity of the tissue-compound upon the surface of the plate, I spread or lead the fluid by means of a glass rod or soft brush, over the entire surface, taking care to avoid the formation of air-bubbles; and I keep the surface in the horizontal position, until the solidification of the tissue-compound. In coating other than plane surfaces, I vary, in a suitable manner, the mode of applying the tissue-compound to such surfaces. In coating a cylindrical surface, I rotate the cylinder in a trough containing the tissue-compound, and after having produced a uniform coating, I remove the trough, and keep up a slow and regular rotation of the cylinder until the coating has solidified. After coating the surface of glass or other substance as described, I place it in a suitable position for rapid drying, and I accelerate this process by artificial means, such as causing a current of dry air to pass over the surface coated, or I use heat, in addition to the current of air, or I place it in a chamber containing quick-lime, chloride of calcium, or other substance of analogous desiccating property. When the tissue is dry, I separate it from the surface on which it was formed, by making an incision through the coating to the glass, around the margin of the sheet; or I cut through the cylindrical coating near the ends of the cylinder, and also cut the coating across, parallel with the axis of the cylinder, when, by lifting one corner, the whole will easily separate in a sheet. When the tissue-compound is applied over a coating of collodion, the film, produced by the collodion, and that produced by the tissue-compound, cohere, and the two films form one sheet. Sometimes, before the separation of the coating from the glass, I attach to the coating a sheet of paper, for the purpose of strengthening the tissue, and making it more easy to manipulate. I generally apply the paper, in a wet state, to, the dry gelatinous surface; and having attached the paper thereto in this manner, I allow it to dry; and I then detach the film and adherent paper from the glass, by cutting around the margin of the sheet, and lifting it off as before described. Where extreme smoothness of surface, such as is produced by moulding the tissue on glass, as described, is not of importance; and where greater facility of operation is desired, I apply a thick coating of the tissue-compound to the surface of a sheet of paper. In this case, the paper is merely used as a means of forming, and supporting temporarily, the film produced from the tissue-compound; and such paper separates from the gelatinous coating in a subsequent stage of my proces. In coating a surface of paper with the sensitive tissue-compound, I apply the sheet, sometimes of considerable length, to the surface of the tissue-compound contained in a trough, and kept fluid by means of heat, and I draw or raise the sheet or length of paper off the surface with a regular motion; and I sometimes apply more than one coating to the same sheet in this manner. After such coating, I place the coated paper where it will quickly dry, and seclude it from injurious light.

“The sensitive tissue, prepared as before described, is, when dry, ready to receive the photographic impression, by exposure under a negative in the usual manner, or by exposure in a camera obscura, to light transmitted through a negative in the manner usual in printing by means of a camera. I prefer to use the sensitive tissue within two days of the time of its preparation. Where the tissue is not required for immediate use, I omit the sensitizer from the tissue-compound as before mentioned; and with this non-sensitive tissue-compound, I coat paper, glass, or other surface, as described in the preparation of the sensitive tissue or paper. In preparing sheets of non-sensitive tissue by means of glass, as described, I use no preliminary coating of collodion. I dry the non-sensitive tissue in the same manner as the sensitive, except that in the case of the non-sensitive tissue, seclusion from daylight is not necessary.

“The non-sensitive tissue is made sensitive, when required for use, by floating the gelatinous surface upon a solution of the sensitizer, and the sensitizer that I prefer to use for this purpose is an aqueous solution of the bichromate of potash containing about two and a half per cent, of this salt. I apply the sensitizer (by floating or otherwise), to the gelatinous surface of the tissue; and after this, I place it in a suitable position for drying, and exclude it from injurious light.

“In applying to photographic printing the various modifications of the sensitive tissue, prepared as before described, I place the sensitive tissue on a negative in an ordinary photographic printing-frame, and expose to light in the manner usual in photographic printing; or I place it in a camera obscura in the manner usual in printing by means of a camera obscura. When the tissue employed is coated with a film of collodion on one side, I place the collodionized side in contact with the negative; or where it is used in the camera, I place the collodionized side towards the light passing through the camera lens. Where the tissue is not coated with collodion, and where paper forms one of the surfaces of the tissue, the other surface being formed of a coating or film of the tissue-compound, I place this last-named surface in contact with the negative; or, when using it in the camera, I present this surface towards the light transmitted by the lens. After exposure for the requisite time, I take the tissue from the printing-frame or camera, and mount it in the manner hereinafter described, that is to say, I cement the tissue, with its exposed surface, or, in other words, with that surface which has received the photographic impression, downward, upon some surface (usually of paper) to serve temporarily as a support during the subsequent operation of developing, and with a view to the transfer of the print, after development, to another surface; or I cement it (also with the exposed or photographically impressed surface downward), upon the surface to which it is to remain permanently attached. The surface, on which it is so mounted, may be paper, card, glass, porcelain, enamel, etc. Where the tissue has not been coated with collodion previous to exposure to light, I prefer to coat it with collodion on the exposed or photographically impressed side, before mounting it for development, but this is not absolutely necessary; and I sometimes omit the coating with collodion, more particularly where the print is intended to be colored subsequently. Or where I employ collodion, with a view to connect the minute and isolated points of the print firmly together during development, I sometimes ultimately remove the film it forms, by means of a mixture of ether and alcohol, after the picture has been finally mounted, and the support of the film of collodion is no longer required. In mounting the exposed tissue or paper previous to development, in the temporary manner, with a view to subsequent transfer to another surface, I employ, in the mounting, a cement that is insoluble in the water used in the developing operation, but that can be dissolved afterwards, by the application of a suitable solvent; or one that possesses so little tenacity, that the paper or other support, attached temporarily to the tissue or paper by its means, may be subsequently detached without the use of a solvent.

“The cements that may be used for temporary mounting are very various, but I generally prefer to use a solution of India-rubber, in benzole or other solvent, containing about six grains of India-rubber in each ounce of the solvent, and I sometimes add to the India-rubber solution a small proportion of dammar-gum, or gutta-percha. In using this cement, I float the photographically impressed surface of the tissue upon it, and I treat, in a similar manner, the paper or other surface intended to be used as the temporary mount or support during development; and, after allowing the benzole or other solvent to evaporate, and while the surfaces coated with the cement are still tacky, I press them strongly together in such a manner as to cause them to cohere.

“When the photographically impressed, but still undeveloped tissue is to be cemented to a surface, that not only serves to support the picture during its development, but also constitutes permanently the basis of the picture, I prefer to use albumen or starch paste as the cementing medium; and where I employ albumen I coagulate or render it insoluble in water (by means of heat, by alcohol, or other means), after performing the cementing operation, and previous to developing. In the permanent, as in the temporary mode of mounting, I cement the tissue, with its photographically impressed surface downwards, upon the surface to which it is to be permanently attached. After mounting the tissue, as before described, and allowing the cement used time to dry, where it is of such a nature as to require it, I then submit the mounted tissue to the action of water, sufficiently heated to cause the solution and removal of those portions of the colored gelatinous matter of the tissue which have not been rendered insoluble by the action of light during exposure in the printing-frame or camera. Where paper has been used as a part of the original tissue; this paper soon becomes detached by the action of the warm water, which then has free access to the under stratum or back of the colored gelatinous-coating, and the soluble portions of it are therefore readily removed by the action of the water; and by this means the impression is developed that was produced by the action of light during the exposure of the tissue in the printing-frame or camera, and the picture remains attached to the mount, cemented to the photographichlly impressed surface previous to development. I allow the water to act upon the prints during several hours, so as to dissolve out the decomposed bichromate as far as possible. I then remove them from the water, and allow them to dry, and those not intended for transfer, but that have been permanently attached to paper, previous to development, I finish by pressing and trimming in the usual manner. Those which have been temporarily mounted, I transfer to paper, card, or other surface. In transferring to paper or card, I coat the surface of the print with gelatine, gum arabic, or other cement of similar character, and allow it to dry. I then trim the print to the proper shape and size, and place its surface in contact with the piece of paper or card to which the transfer is to be effected, such piece of paper or card having been previously moistened with water, and I press the print and mount strongly together; and, after the paper or card has become perfectly dry, I remove the paper or other supporting material, temporarily attached, previous to development, either by simply tearing it off, where the cement used in the temporary mounting is of a nature to allow of this without injury to the print, or I apply to the temporary mount, benzole or turpentine, or other solvent of the cement employed, or I immerse the print in such solvent, and then detach the temporary mount, and so expose the reverse surface of the print; and, after removing from the surface of the print, by means of a suitable solvent, any remains of the cement used in the temporary mounting, I finish the print by pressing in the usual manner. If, however, the print be collodionized, and be required to be tinted with water-color, I prefer to remove the collodion film from the surface of the print, and this I do by the application of ether and alcohol.

“Having now set forth the nature of my invention of ‘Improvements in Photography,’ and explained the manner of carrying the same into effect, I wish it to be understood, that under the above in part recited letters-patent, I claim: First, the preparation and use of colored gelatinous tissues in the manner and for the purpose above described.

“Secondly, the mounting of undeveloped prints, obtained by the use of colored gelatinous tissues, in the manner and for the purpose above described.

“Thirdly, the re-transfer of developed prints, produced, as above described, from a temporary to a permanent support.”

It will be seen that one of the essential features of the process is the production of a “tissue,” which renders the manipulations necessary to perfect results practical and easy, which were before difficult or impossible. We shall see in the historical notes which follow that the principles upon which carbon printing is based had received partial recognition at an early period. As they became more perfectly understood the practical difficulties seemed greater. The imperative condition upon which half-tone depends, the exposure of one side of the film to light, and of the other to the solvents which should remove the unaltered material, seemed to present an insuperable difficulty. Exposure through the prepared paper was attended by two grave difficulties: the passage of the light through the paper, rendered yellow by saturation with the bichromate, was exceedingly protracted; and actinic force transmitted by the negative was to a great extent arrested before it reached the sensitive coating of gelatine and pigment, a brown tint (highly adiactinic) being formed in the texture of the paper. The intervening paper between the negative and sensitive layer is further objectionable on account of the loss of brilliancy incidental to its becoming more deeply brown where the shades of the print come, and consequently offering a proportionally greater obstruction to the light there than elsewhere. Besides, the finished picture, no matter how delicate the negative, bore marks of all the granulation or defects in texture of the paper through which the light passed. The ingenious device of M. Fargier, in which the sensitive coating was applied to a plate of glass, and, after exposure, transported from the glass, by the aid of a film of collodion, in order to wash away or develop on the opposite side of the film, was manifestly impractical on a commercial scale, especially for large pictures, owing to the difficulty of manipulating a thin film of gelatine attached to a thin film of collodion, floating in a vessel of water; and the difficulty, almost amounting to impossibility, of transferring such a film perfectly to paper. The “tissue” described in Mr. Swan's specification, together with the series of ingenious devices accompanying its use, have been the means of effectually overcoming the many practical difficulties above enumerated, and of making the production of carbon prints, of any size, in any number, and of unimpeachable quality, a thing commercially practicable.

There are two modes of proceeding in forming the tissue, either of which may be adopted, as circumstances may render desirable. The first consists in coating a plate of glass with plain collodion, and upon this film applying a mixture of gelatine, sugar, coloring matter, and bichromate of potash. When this is dry, it is removed from the glass, and forms a pliant tissue, ready for exposure under a negative, after which it is mounted (exposed face down) on paper, either temporarily, by means of caoutchouc cement, or permanently, by means of albumen. It is then developed, and, if temporarily mounted, is re-transferred, as we shall describe. The second and usual method consists in the application of the gelatine and coloring matter to paper, which can be rendered sensitive, when required, by immersion in a solution of bichromate of potash. It is then exposed under a negative, attached to another temporary basis of paper by a waterproof cement, the first paper being readily removed by soaking in warm water, so as to expose to the water the side of the film-opposite to that which was in contact with the negative, the development and transference following in due course. We shall describe both these methods in detail.

A patent has been issued to John C. Crosman, Boston, Mass., for an "Improved Process of Coating Sheets of Paper and Other Material with Solutions." His specifications read as follows:

"My invention relates to a process by which sheets of various material, such as leather, cloth, paper, etc, are covered by a coating applied in the form of a fluid, or a fluid solution, in such a manner that the resulting coating will be smooth and of uniform thickness, and so that when the solution applied contains chemical salts these will be equally distributed over the surface which is so covered. Said process consists in first thoroughly moistening or saturating a sheet which is to be coated, which I do preferably by immersion in suitable fluid, which may be cold or heated, according as one or the other condition is best adapted to produce the desired effect; then, in depositing the dampened sheet on a level table, and by suitable manipulation causing the sheet on its under side to come into contact with the upper surface of the table, by expressing air and any free fluid from between the sheet and table; and also, where found necessary, removing superfluous fluid from the upper surface of the sheet, by application thereunto of bibulous paper, or other suitable absorber or remover; and finally, in applying to the upper surface of the sheet, when in the condition produced by the second operation, a fluid material, or a fluid solution of the material or of the mixture, with which the said surface is to be coated. In practice the level table top should be made of substances not changeable in form on the application of fluid, and glass, slate, marble, or metal may be used, though I prefer glass.

“In applying the solution, which, upon drying, forms the desired coating of the sheet, and where the solution is of such a nature that but a small quantity will leave or deposit the requisite coating, I proceed in the manner of water-color artists when laying broad washes of flat tints. But when a considerable quantity or depth of fluid is required to make the desired coating, I then make use of such a frame as paper-makers term a deckle (the bottom of which may be faced with rubber), placing it on the top of the table around the paper, the edges of which the inside of the frame nearly touches. I then pour on the paper a suitable quantity of solution, which gravitates into uniform depth on the paper, it being prevented from flowing off from the paper by the deckle. In some cases the distribution of solution may be aided by the operator's use of a brush.

“In applying the solution use may be made of a reservoir, caused to traverse over the table, and delivering the solution uniformly over the breadth of the sheet while so passing; and, if desired, the solution may be made to flow into or upon a brush attached to said reservoir, and coming into contact with the sheet, while the amount of the solution delivered may be made to depend upon a suitable valvular arrangement, and the speed with which the reservoir is moved. With this reservoir may be employed the deckle, especially if considerable depth of solution is to be left upon the surface of the sheet. “While this process was devised by me with reference to the preparation of paper for use by photographers, I do not by any means consider it as limited to such use, as sheets of material may be coated in the manner described with alcohol, aqueous, alkaline, or acid solutions, or with fused resins, oils, varnishes, or paints But care must be taken to have the fluid, with which the sheet is saturated, one with which the covering or coating solution or fluid has an affinity.

“The object of thoroughly and uniformly saturating the sheets before applying them to the table is to cause them to lie flat thereupon, so that, if the sheet is of uniform thickness, there will be no valleys in which the deposit of coating matter will be thick, or hills on which it will be thin.”

It will be seen that the patent issued to Mr. Crosman is only for making tissue for use by the Swan, or other processes described hereafter. What arrangements, if any, will be made to allow the photographers of this country to use Mr. Swan's process we cannot yet say, but we are assured that no interference whatever will at present be made with any one who may feel inclined to take it up and experiment with it. A great many have already done so, and are also making their own tissue. The making of the tissue is troublesome, and it is more economical to buy it of the dealers. Great credit, honor and praise is due to Mr. Swan for his process, and the whole world is indebted to him. We had heard that Mr. Swan's and the Crosman interest had been combined, but there has been no public announcement of such a combination. We suppose it is not Mr. Swan's intention to disturb those who are working his process in this country at present. In time, he will no doubt announce his plan for licensing.

A number are now using the process, and have been doing so for two years without interference, and we believe all are safe in doing the same.

We now proceed with the details of the process as worked by Mr. Swan, adding a few foot-notes, giving our experience wherever it differs from that described so fully and so plainly by Mr. Simpson.