This is a process for the production of photo-lithography in half-tone, direct from the negative, without the intervention of a collotype plate from which to pull the transfer, and is a distinct step in advance.
This process has been named papyrotint, being a modification of Captain Abney’s improved method of photo-lithography, named papyrotype. It is specially adapted to the reproduction of subjects in half-tone, such as architectural drawings in monochrome, or subjects from nature, and it is inexpensive. Its advantages over other methods of half-tone photo-lithography are, that a transfer can be taken in greasy ink, for transfer to stone or zinc direct from any negative, however large, without the aid of a medium, the grain or reticulation being obtained simply by a chemical change. The transfer paper being in direct contact with the negative, the resulting prints are sharper than by those processes where interposed media are used; whilst the same negative will answer either for a silver print, platinotype, or a transfer for zinc or stone. The advantage of being able to use a non-reversed negative is very great, now that gelatine plates have so largely superseded those made with collodion.
The method of manipulation is as follows: Any good surface paper is floated twice on a bath composed of
| Gelatine (Nelson’s Flake) | 8 | ounces. |
| Glycerine | 1 1⁄2 | ounces. |
| Chloride of Sodium (Common Salt) | 2 | ounces. |
| Water | 50 | ounces. |
Great care should be taken that the solution is not overheated, and that the paper is coated without bubbles. It is then dried in a temperature of 60° F. The paper will take about ten hours to dry, and in this state will keep for years. When required for use, it should be sensitized by floating on, or immersing in, a bath of
| Bichromate of Potash | 1 | ounce. |
| Chloride of Sodium | 1⁄2 | ounce. |
| Ferridcyanide of Potassium | 100 | grains. |
| Water | 30 | ounces. |
This need not be done in a dark-room, as the solution is not sensitive to light.
The paper, after sensitizing, is dried in a temperature of 70°, and in a dark room. When dry, it is exposed under any half-tone negative, in the ordinary printing frame. It is preferable to print in sunlight, and, for negatives of medium density, an exposure of three minutes is required; but the exposure will vary according to the density of the negative. The correct time of exposure can best be judged by looking at the print in the frame. When the image appears on the transfer paper of a dark fawn color, on a yellow ground, the transfer is sufficiently printed. It is put into a bath of cold water for about ten minutes, until the soluble gelatine has taken up its full quantity of water; then taken out, placed upon a flat piece of stone, glass, or zinc plate, and the surface dried with blotting paper.
The action of the light has been to render the parts to which it has penetrated through the negative partly insoluble, and at the same time granulated. A hard transfer ink is now used, composed of
| White Virgin Wax | 1⁄2 | ounce. |
| Stearine | 1⁄2 | ounce. |
| Common Resin | 1⁄2 | ounce. |