This section is from the book "Complete Self-Instructing Library Of Practical Photography", by J. B. Schriever. Also available from Amazon: Complete Self-Instructing Library Of Practical Photography.
This transfer is absolutely necessary on account of the image being formed under the surface of the tissue, which is insoluble. Therefore, in order to develop the concealed image it is necessary to transfer the carbon tissue to another support and develop from the back of the tissue, where the light has not penetrated, and the gelatin, in consequence, is unaltered.
233. Carbon pictures are developed with plain hot water, which softens the paper or original support and makes soluble the unaffected parts of the gelatin, which then allows the paper to be removed. The image is thus exposed to the action of the hot water, which dissolves and washes away all the soluble parts, and with it the pigment or coloring matter its contained, thereby clearing the image and effecting the development.
The Single Transfer. If a carbon tissue which has been regularly exposed (printed) under a negative is placed in a tray of cold water, and allowed to absorb the water until' the tissue begins to flatten out, and is then brought into intimate contact with a specially prepared paper or any smooth material impervious to water, such as transfer paper, celluloid, porcelain, etc., the pigment paper will firmly adhere to these during the process of development, providing all the conditions pertaining to the sensitizing and drying of the tissue have been strictly adhered to, and will dry down with a smooth surface, where it will remain permanently and will not leave the support.
235. This is called the single transfer process, on account of the one transfer and because the image is developed upon the final support. This process is used almost exclusively by the majority of the carbon printers, and the resulting pictures are as good as the more difficult double transfer process, the only difference being that the pictures printed from the ordinary negative are reversed.
236. Where negatives are made specially for carbon printing, this obstacle may be overcome by reversing the plate in the holder, glass side to the lens, and when making the exposure you do so through the glass onto the film. You should invert the ground-glass in the camera with the ground surface on the outside to assure a sharp focus. Usually, a reversal of the image is not objectionable, especially in portraiture; therefore, we advise making the negatives in the regular way and using single transfer process. No one will know the image is reversed except the printer. If the print is being made from a film, it is, of course, only necessary to print through the back of the film to obtain a correct image; the slight thickness of the film will not mar the sharpness of the print to any material extent.
Carbon Supports. The final support for single transfer can be procured already prepared, in all grades and kinds. The paper supports are supplied by dealers, in cut sizes, large sheets, or rolls. There are different grades-smooth, medium, rough, etc. One side of this paper is especially prepared for receiving pigmented paper. The coating is such that water will not penetrate through it, thus supplying a solid, impervious support. The paper is coated with a substratum of insoluble gelatin, which may be distinguished from the uncoated side, when dry, by its lustre. The gloss is not noticeable when wet; therefore, as a precaution, mark the back of each piece of paper before immersion.
238. Any kind of paper already prepared may be used as a final support. For very artistic effects heavy, coarse drawing paper prepared with the same substratum will supply a good support.
239. To prepare paper specially for support, coat with the following solution:
White sugar ..........................
240. Soak the gelatin in the water for about one hour; add the sugar, and then melt the gelatin by placing the vessel containing it into hot water. Procure a kettle larger than the vessel containing the gelatin, and pour one quart of water into it and place it on a stove to boil. Into this kettle of boiling water place the vessel containing the gelatin, and allow the water around it to boil. When the gelatin is thoroughly melted, dissolve the chrome alum (80 grains) in two ounces of water, and add this chrome alum solution, a few drops at a time, to the gelatin, and stir vigorously while the water is boiling around the inner vessel. If the mixture should thicken up, add one-half a dram of glacial acetic acid. Stir well until the mixture is quite limpid. Filter this mixture while still hot into a tray which should be a little larger than the sheet of paper which is to be coated. With wood clips, attach a thin strip of wood on the back of the sheet to both the top and bottom, and float the paper on the bath. Hold the paper over the bath with both hands and carefully lower the end in the right hand first; then gradually raise the right hand, at the same time lowering the left. Repeat this operation about four times.
241. Now lay the paper, face side up, on a clean blotter and examine the surface for bubbles. If any exist, dip a small camel's-hair brush into the gelatin mixture and cover these spots evenly. A much more convenient, and equally as good, way to coat the paper is to lay it on some smooth surface and with a three-inch camel's-hair brush apply the gelatin mixture evenly over the sheet. As soon as the mixture is set, the sheet may be suspended in your drying-room, away from dust, to dry. Paper so prepared will keep for any length of time, providing it is stored in a perfectly dry place.
242. The substratum, or gelatin mixture, which is left after preparing what paper you need, should be returned to the vessel in which it was prepared and saved for future use.