Science Fair Project Encyclopedia
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 using a developere based on conventional black and white film developer. However, the developer also includes specififc additions to develop the dye-couplers in the film emulsion layers into visible dyes. The control of temperature and agitation of the film in the developer is critical in obtaining consistent results. Development is followed by immersion in a mildly acidic stop bath or rinse to halt the development action, and then by a combined bleach-fix which both dissolves the silver generated by development and removes undeveloped silver halide. This is 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 converts the photographic silver halides into black metallic silver. All C-41 films also include an additional orange coloured dye-layer to offset the optical inadequacies of the dye layers in the film. C-41 negatives always appear orange when viewed directly but this orange base is compensated for in the formulation of colour print materials.
The finished negative may then be printed using colour photo paper to get a positive image.
While C-41 usually considered a color process, Kodak manufactures chromogenic black and white films such as BW400CN and T400CN that are processed using the C-41 process. Ilford also made XP2 Super before they ended their business in 2004. Commercially produced prints from these brands of film will often 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, except for the absence of grain in the image. These films have the advantage that they can be processed by one hour photo shops, and although rated at 400 ISO they have a wide range of exposure at which they will yield a usable negative, between 100 and 800 ISO.
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