A fixer is a chemical solution that removes the undeveloped silver halide crystals from films. Fixer also helps to harden the gelatin containing the black metallic silver so the film may be dried more readily.

Chemical, usually acetic acid in the fixer and sodium carbonate in the developer, to neutralize the developer and to swell the gelatin, respectively.

See also Film Processor and X-Ray Film.

Chemical, usually ammonium thiosulfate, added to the fixer to remove undeveloped silver bromine from the film emulsion.

A developing agent is a chemical, usually phenidone, hydroquinone or metole, which reduces exposed silver ions to atomic silver to visualize an image on a film.

See also X-Ray Film, Film Processor, Activator, Clearing Agent, Developer and Fixer.