C-41 process

C-41 is the name given to the process for developing a specific type of color film used in photography and often to the type of film itself. At the time of this writing, C-41 is the most popular film process in use, with just about every photofinishing lab having at least one machine specifically devoted to developing this type of film.

The film for C-41 consists of a gelatin base overlaid with colored emulsions. When exposed to light different colored dyes in the emulsions act as filters so that specific layers within the emulsions are sensitive to different colors in the optical spectrum. The film is then developed as most photographic films and papers are developed: first by soaking in a bath of developer, next a quick stop bath or rinse to halt the development action, then by fixing, followed by thorough washing. This process is fairly familiar in photography, but for C-41 the chemical composition and relative strength of the developer and fixer are unique and specific, as is the way the emulsions are laid on the base.

The resulting film is a negative, meaning that the darkest spots on the film are those areas that were brightest in the source. This result occurs because it is exposure to light and development that turn photographic silver salts black. The negative may then be printed using photo paper to get a positive image.

While C-41 usually considered a color process, the Ilford company does make a brand of black and white film, XP1, that works with the C-41 process. Typically prints from this brand of film done at a retail photofinisher will have a colored hue to them, but printed on standard black and white papers they are indistinguishable from images made using standard black and white films.