with the prepared surface next the negative, mounting with a solution of shellac and Venice turpentine in alcohol, or with albumen, and then coagulating; soaking until the original paper leaves the gelatine and pigment, and then developing with hot water.
It is not necessary to mention all the minor modifications of Swan's method which were proposed; nor the various suggestions which grew out of the discussion of his process. We may, however, mention one or two of the latter. Mr. Frank Eliot suggested taking advantage of M. Poitevin's last process with perchloride of iron and tartaric acid. He proposed working with black paper, coating it with gelatine and white pigment, sensitizing with the iron salts and tartaric acid; then exposing, and developing, to obtain an image in white pigment on a black ground. If any attempt were made to carry out such a scheme, it is obvious that a pigment must be found which would not decompose the iron salt or be affected by it.
During the following year, Mr. M. Carey Lea published working details of two processes, both of which were analogous to some of the earlier processes. In the first,[1] the paper was prepared with a mixture of gelatine, glycerine, bichromate of potash, and water; and, after drying, was exposed under a positive cliché. The parts intended to form the lights become hardened and insoluble; the shadows, being protected from the light, swell and soften, but do not dissolve on immersing the print in cold water. The prints are left soaking, to remove as much of the color of the reduced chromic salt as possible from the lights; and afterwards, finely-powdered lampblack is applied, which adheres to the softened gelatine, and forms the picture. Mr. Lea points out that,
- ↑ “Philadelphia Photographer,” vol. ii.
