Paper is impregnated with primuline either by floating or brushing. The best results are obtained with paper previously sized with arrowroot or gelatine in order to keep the image entirely on the surface of the paper.
Linen, silk and wool are treated as calico.
The clichés should be positive to obtain positive expressions and somewhat more opaque than those employed in the processes before described, else vigor and intensity could not be obtained. Here we must state that the primuline process seems to be better adapted for the reproductions of drawings, such as made for the black process, and of opaque photo-clichés in lines, or white and black, than for printing in half tone.
When the material to print upon is thick and wholly impregnated with diazotized primuline, it is advisable, since the insulation could not be prolonged to effect the change through, to expose the back of the material for a certain but [pg 54] short period in order to clear it. This is especially advantageous when the cliché is not of good intensity.
During the exposure, which varies from 30 seconds to 10 minutes and more by a dull light, the progresses of the luminous action is seen by the bleaching of the material which assumes a dingy coloration. But in order to ascertain when the decomposition is complete on the ground of the image, it is well to use tests as in the cyanofer process, dipping one of them in the developer from time to time.
The developers are compounded as follows:
| FOR RED. | |
|---|---|
| Beta-naphthol | 4 parts |
| Caustic potassa | 6 parts |
| Water | 500 parts |
Rub the alkali and the naphthol with a little water in a mortar and add the remainder of the water.
| FOR ORANGE. | |
|---|---|
| Resorcin | 3 parts |
| Water | 500 parts |
When dissolved add