Gelatin is used to hold silver halide crystals in an emulsion in virtually all photographic films and photographic papers. Despite some efforts, no suitable substitutes with the stability and low cost of gelatin have been found.
It is also used as a surface sizing it smoothes glossy printing papers or playing cards and maintains the wrinkles in crepe paper.
Photographers' Formulary 10-0590 1LB Specs
Colorless or light yellow, transparent, brittle, practically orderless sheets, flacks, or coarse powder.
Preparation of emulsions Sizing paper Adhesives Light filters
Gelatin contains a large number of glycine (almost 1 in 3 residues, arranged every third residue), proline and 4-hydroxyproline residues. A typical structure is -Ala-Gly-Pro-Arg-Gly-Glu-4Hyp-Gly-Pro-.
Swells up and absorbs five to ten times its weight of cold water.