The negative for this process must contain all the details very clear, must be soft, and not be too dense.
The different colour plates are thus in this process obtained by long or short printing, by strong or weak developing, and finally the details in the dark plates are obtained by separate development and covering up the other places with gum.
The breaking up of the half-tones into printable grain is effected by graining the stone, before coating with the light sensitive asphalt film. On the finer or coarser graining of the stone depends also the structure of the grain of the image.
This process yields the most beautiful results with correct manipulation, and in the hands of an expert photographer and lithographer is a valuable aid to the preparation of colour plates. The process is patented.
(C.) J. BARTÖS’ PROCESS FOR PREPARING PHOTO-LITHOGRAPHS AND PHOTOTYPES IN GRAIN AND HALF-TONE.
Bartös’ process belongs to those in which the breaking up of the half-tones into a printable grain is effected subsequently on the plate or stone by mechanical means. This is attained in a very original manner by means of a sandblast, which makes the half-tone printable. We have here not the breaking up of the half-tones in a mathematically regular manner, dependent on optical laws, as is the case with autotypy, but a method similar to that of Pretsch, which obtains the printable grain by reticulation of the chromated gelatine film, or other discoverers who attain the same result by asphalt dusting or some other means.
For this process a well-polished litho stone or zinc plate is coated with a thin film of varnish, composed of—
| Chloroform | 300 | g. |
| Mastic | 5 | g. |
| Asphalt | 10 | g. |
| Benzole | 300 | g. |
| Linseed oil | 2 | g. |
On the stone or plate thus prepared is transferred a carbon image in half-tone.
This pigment film, when completely dry, is flowed over with a mixture of—