Photographic fixer

Chemicals used in photographic processing of film

Photographic fixer is a mixture of chemicals used in the final step in the photographic processing of film or paper. The fixer stabilises the image, removing the unexposed silver halide remaining on the photographic film or photographic paper, leaving behind the reduced metallic silver that forms the image. By fixation, the film or paper is insensitive to further action by light. Without fixing, the remaining silver halide would darken and cause fogging of the image. Fixation is commonly achieved by treating the film or paper with a solution of thiosulfate salt. Popular salts are sodium thiosulfate—commonly called hypo—and ammonium thiosulfate—commonly used in modern rapid fixer formulae. Fixation involves these chemical reactions (X = halide, typically Br−):AgX + 2 S2O32− → [Ag(S2O3)2]3− + X− AgX + 3 S2O32− → [Ag(S2O3)3]5− + X−

This keyword could refer to multiple things. Here are some suggestions: