Tanning, Photographic

the chemical processing of the light-sensitive gelatin layers of photographic materials in order to increase their mechanical strength and heat resistance and to reduce their swelling in water and aqueous solutions. Both inorganic substances (chromium or aluminum-potassium alums and chromium acetate) and organic substances (Formalin, glyoxal, and others) are used as tanning agents. Tanning agents are often introduced into the photographic emulsion during the manufacture of the photographic materials. If the tanning of the gelatin layer thus produced is insufficient, then photographic tanning is carried out during developing (some developers, such as pyrogallol and pyrocatechol, have a tanning action at the same time) and, most frequently, during fixing. Fixing solutions that contain tanning agents are called tanning fixers.