as in this process the lights are embodied in the shadows, and no part is washed away, there is no danger of losing the half-tones, as in some processes; and that he thinks it is possible to obtain some degree of gradation by this method.
The second process proposed by the same gentleman[1] is avowedly for the reproduction of subjects without half-tone. In this process he employs a mixture of gum-arabic, albumen, glycerine, double chromate of potash and ammonia, powdered graphite, and water. The mixture is of the thickness of honey, and is applied to the paper with a broad brush. When dry, it is exposed under a negative of any subject in line or stipple. After exposure, the right amount of which may be ascertained by examining the back of the print, it is developed by soaking in cold water, which removes the unaltered material, leaving clean lights and good blacks.
A more recent suggestion for a method of carbon printing was made in the course of last year by Dr. Gotschalk. He observes that graphitic acid, a substance prepared by the action of nitro-sulphuric acid upon graphite, is sensitive to light, which deoxidizes it, reducing it again to the condition of graphite. Hence it was proposed to prepare paper with a solution of this body, and expose it under a negative to the action of light. The first difficulty in the way is its insolubility, or sparing solubility, in any available menstruum. The trace, dissolved by water, applied to paper, is sufficient to color the paper brown when exposed to light. A method of checking its action, or fixing the print, would also be required. No practicable application of this substance for this purpose has yet been found.
Although Mr. Swan has perfected a process for us, by
- ↑ “Photographic News,” vol. ix, p. 459.
