Photographic fixer

For other uses, see Fixer (disambiguation).

Photographic fixer is a chemical, or mixture of chemicals, used as the final step in the photographic processing of film or paper. The fixer stabilises the image, removing the unexposed light-sensitive material from the media, and making it insensitive to further action by light.

In the gelatin silver process, the basis for all film photography, exposed silver halides are reduced to metallic silver by the developer, forming the image. Once development is complete, remaining silver halides are removed from the film or photographic paper by the fixer, typically sodium or ammonium thiosulfate. Without fixing, the remaining silver halide would darken and cause fogging of the image.

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