Photo-activity of Bichromated Colloids

Abstract

THE hardening of bichromated colloids, forming as it does the basis of nearly all photo-engraving processes, is of great importance in the printing industry. In the photogravure process the colloid used is gelatine which is coated on paper to form carbon tissue. This is activated by immersion in a solution of potassium bichromate, which in practice is frequently rendered alkaline by the addition of ammonia. We are at present studying the effect of pH of the gelatine and of the bichromate solution on the photographic qualities of the tissue.