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.

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.