<P> All processes based upon the gelatin - silver process are similar, regardless of the film or paper's manufacturer . Exceptional variations include instant films such as those made by Polaroid and thermally developed films . Kodachrome required Kodak's proprietary K - 14 process . Kodachrome film production ceased in 2009, and K - 14 processing is no longer available as of December 30, 2010 . Ilfochrome materials use the dye destruction process . </P> <P> All photographic processing use a series of chemical baths . Processing, especially the development stages, requires very close control of temperature, agitation and time . </P> <Ol> <Li> The film may be soaked in water to swell the gelatin layer, facilitating the action of the subsequent chemical treatments . </Li> <Li> The developer converts the latent image to macroscopic particles of metallic silver . </Li> <Li> A stop bath, typically a dilute solution of acetic acid or citric acid, halts the action of the developer . A rinse with clean water may be substituted . </Li> <Li> The fixer makes the image permanent and light - resistant by dissolving remaining silver halide . A common fixer is hypo, specifically ammonium thiosulfate . </Li> <Li> Washing in clean water removes any remaining fixer . Residual fixer can corrode the silver image, leading to discolouration, staining and fading . </Li> </Ol> <Li> The film may be soaked in water to swell the gelatin layer, facilitating the action of the subsequent chemical treatments . </Li>

Which chemical makes it possible for a photograph to be exposed to be open to white light