Wood panels are prepared by removing the surface of the paint only with soda solution. After drying, a tooth is given by rubbing with fine sand paper and coating with solution as under:—
| Gelatine (Cox's soup) | 3 | oz. |
| Sugar | 1 | " |
| Glycerine | ½ | " |
| Water | 30 | " |
| 30 grain chrome alum solution | ¾ | " |
Note.—Before transferring to either kinds of canvas or wood panel in cold weather, it is absolutely necessary to thoroughly warm the final support, otherwise the gelatine solution will gelatinize before the excess can be removed from between the surfaces.
THE SINGLE TRANSFER PROCESS.
The single transfer process may be briefly described as follows:—The sensitive tissue is exposed under a negative and the exposure gauged by actinometer as for double transfer printing. After removal from the pressure frame the printed tissue is plunged into clean cold water along with a piece of transfer paper of any desired surface or quality, cut a little larger than the tissue (to provide a margin by which the picture may be handled without injury during development). After soaking the requisite time, the two prepared surfaces are brought into contact under the water, removed to a squeegeeing board, plate of glass or zinc, and squeegeed into contact; care must be taken to use only as much pressure as is needed to remove the superfluous water from between the surfaces. A sponge may be used instead of a squeegee, or both may be dispensed with, if care is taken to remove every trace of air from surfaces before lifting from the cold water bath. When neither squeegee or substitute for it is used, the print must be handled with greater care, as undue bending before atmospheric pressure comes into operation would destroy contact. The print is hung up to drain, and more time allowed between mounting and development. Development is the same as in double transfer, with one or two rather important exceptions. 1st. The single transfer print is developed upon the material on which it is to remain. 2nd. There is no preparation of the supports, neither in the case of paper or opal. 3rd. The developed print can be soaked for a considerable time in a saturated solution of alum without injury, the alum solution greatly assisting in removing bichromate.
CARBON TRANSPARENCIES.
Carbon transparencies, either for projection, enlargement, or reproduction, are printed in a special tissue known as transparency tissue, and developed on glass plates prepared with a thin coating of fine hard gelatine. The coating solution is composed as follows:—
| Gelatine | ¾ | oz. |
| Water | 40 | " |
| Bichromate potash | 1 | dram. |
The glass plates are carefully selected, free from bells, scratches, and other defects; thoroughly cleaned, either by acid or rubbing with plate powder to remove every trace of grease, and then coated with the gelatine solution, and placed in a rack to dry; when dry, exposed to light to render the film somewhat insoluble. It is not desirable to print until the film is absolutely hardened throughout. The print adheres firmly to the plate when the substratum is not over-printed.
A positive intended for projection should show clear glass in the highest lights without undue density in the shadows, all details plainly seen—in a word, quite transparent.