Photographic fixer

A fixing agent is in the photography a chemical which renders the exposed light sensitive film. Through a bath in the chemical, the chemical structure of the film is changed so that the light-sensitive substances of the film material are converted into light-sensitive substances. This then allows further processing and subsequent storage of the resulting film from the negatives.

The fixing of a movie is a thiosulfate solution nowadays. This exploits that the thiosulfate ion ( S2O32 - ) forms a stable complex with the silver halides. During the fusing process, the present as a solid silver bromide is converted via several intermediate steps in water-soluble compounds:

(1)

(2)

(3)

(4)

The now in the solution Dithiosulfatoargentat (I ) complex is easily washed out and the film thus fixed, because when exposed to light now no more silver halides can be converted to silver, as no more silver halides are present.

Earlier (NH3 ) was used as a fixing agent ammonia. Ammonia forms a similarly stable complex [ Ag (NH3 ) 2] X - is the Diamminsilber (I ) halide. The X stands for the halide anions (Cl -, Br -, I- ).