How Does Color Film Developing Work?
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What is color film?
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For color film developing or chromogenic film developing, most people use color negative film in their point and shoot cameras, but color reversal film or slide film is also used. Color negative film forms a silver color-reversed image when exposed by a camera's shutter and is then fixed into a positive color dye image. Slide film is also reversed into a positive image during developing but is made into a slide and can then be projected onto a screen or be viewed on a backlit slide table.
C-41, the most common film, has multiple layers of emulsion on it which are each sensitive to a different wavelength of light and have dye couplers in the layers so the blue, green and red layers also have yellow, magenta and cyan dyes.
Developer
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When a photographer wishes to develop a color photo or a roll of color film, it is put through a five-step process similar to black and white film in a dark room so that the film does not attain accidental extra exposure. The film is first put in a color-developer bath with the CD-4 ingredient (Paraphenylene Diamine). This develops the silver in the emulsion layers while the oxidized developer reacts with the dye couplers, forming the colors.
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Bleach, stop-bath
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The film is then put into a bleach stop-bath which prevents the alkaline developer from going overboard and over developing the image. Stop baths can be made of acetic acid, citric acid, or plain water and an automatic squeegee like in 1-hour processing machines.
Fixer
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A fixer, like the name states, allows the image in the film to remain permanent by washing away any of the remaining chemicals. Fixer is made of salts such as sodium thiosulfate or ammonium thiosulfate. If traces of silver halide are left on the photograph it can become foggy and dark. In contrast if traces of the fixer are left on then the picture can become washed out and bleached so the next process is just as important.
Washing and Drying
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Washing the photograph is one of the last steps and must be done thoroughly. The water wash must be fresh and clean each time it is used. Hypo Clearing Agents are sometimes used in place of water. Lastly the film is dried in a proper dust-free environment and can then be printed on color paper.
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