A photographic material consists of a base made of a sheet of plastic film, glass, or paper coated

with a photographic emulsion (consisting of a polymeric material such as gelatin containing

numerous fine crystals of light-sensitive silver halide). Silver halides used in photographic

emulsions include silver bromide, silver chloride, silver iodide, or mixtures of these. Exposure of

this photographic emulsion to light results in the formation of a “latent image,” a four-to-ten

atom speck of metallic silver on the silver halide crystal. In simplified terms, light striking

molecules of silver halide (AgX) in the emulsion causes some of them to be reduced to metallic

silver (Ag0) atoms.