Photographic fixer

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.

[1] Fixation by thiosulfate involves these chemical reactions (X = halide, typically Br−):[2] In addition to thiosulphate the fixer typically contains mildly acidic compounds to adjust the pH and suppress trace amounts of the developer.

In chromogenic films, the remaining silver must be removed by a chemical mixture called a bleach fix, sometimes shortened to blix.

This mixture contains ammonium thiosulfate and ferric EDTA, a powerful chelating agent.

A black and white photographic print in a tray while being processed after exposure to light under a photographic enlarger. Typically three trays are used containing either developer, stop bath, or fixer, in that order. The print must then be rinsed in water to removed the fixer.