For black and white photography, the developer is often a mixture of metol and hydroquinone. These are made up in aqueous solution with sodium carbonate to create the appropriately high pH and sodium sulfite to provide strong reducing conditions to delay oxidation of the developing agents by atmospheric oxygen.
Most developers also contain small amounts of potassium bromide to modify and restrain the action of the developer to enable penetration of the developer throughout the emulsion before over-development occurs on the surface - < ...
In many colour transparencies, the film is first processed in a sophisticated black and white developer and is then treated with a 'reversal chemical which stops the initial development and converts the previously unexposed silver into the new latent image. The film is developed again using a process similar to C41 before final fixing and washing. The most common processing chemistry for such films is E6, derived from a ...
The developer reduces the silver halides in the latent image in the exposed photograph into reduced, opaque, black silver metal. The image is then fixed using photographic fixer.
The mechanism by which this reduction occurs preferentially on those halide grains containing the silver atoms of the latent image is complex. The developer molecule (typical a relatively simple benzene-ring molecule) may act as an 'electron brid ...
