| FOR YELLOW. |
|---|
| Carbolic acid, cryst | 5 parts |
| Water | 500 parts |
| FOR PURPLE. |
|---|
| Naphthylamine | 6 parts |
| Hydrochloric acid, in volume | 6 parts |
Mix in a mortar, then add
| FOR BLACK. |
|---|
| Eikonogen, white crystals | 6 parts |
| Water | 500 parts |
Pulverize the eikonogen, add the water and, at the same time, the material on its removal from the printing frame, and keep in motion until the development is effected.
| FOR BROWN. |
|---|
| Pyrogallol | 5 parts |
| Water | 500 parts |
After the development, which requires but a few moments, it suffices to wash the material to fix the image by eliminating the soluble compounds. However, for purple the material should be passed in a dilute solution of tartaric acid and not washed afterwards; it should remain acid.
When it is desirable to obtain an impression in several colors, the various developers are thickened with starch, then locally applied with a brush on the image, which is always visible after exposure.