C-41 process

C-41 is the photographic film process used to develop practically all modern still-picture color negative film. It is also used for some black and white films, such as XP2. Slide film can also be cross-processed in C-41 to produce a negative.

A C-41 negative (left), and the same image inverted to produce a positive (right)

How the process works

C-41 film has a safety (acetate or polyester) film base, tinted orange on most films, with an emulsion made of silver halides and dye couplers. These are in multiple layers that record each primary color separately. When the film is developed, the silver is developed first, like black and white film. Oxidized developer then reacts with a dye coupler to produce a visible dye. The film is then bleached and fixed, which removes the silver and unexposed silver halides, making the image permanent. The film cannot be exposed to any light, not even the red darkroom safelight, until the process is completed. The film can then be printed with the RA-4 process, or scanned into a computer.