FOTOLAC - deep etch coating for PHOTOENGRAVING :
Negative Photoresist . One of the oldest type of photoresist based on PVA. Develops in water. It is used for coating on the zinc and steel plates to be resistant in the nitric acid tanks to form shoulders. Fotolac produces a tough stencil and this makes it ideal coating for producing multi-metal plates.
Sensitizer for Fotolac. Add 50 ml. in 1 lt Fotolac.
CHROMIC ACID to harden and strengthen the stencil:
Dilute 420 gr chromic acid (flake form) in 4 lt. of water. After developing the plate in the water, wash the plate in the chromic acid solution for 30 sec. By doing this, the image on the plate has a darker color. If the plate is kept less than 30 sec. in the solution the image has a weaker resolution, or if the plate is kept more than 30 sec. in the solution the image decays.