An emulsion of sodium thiosulfate (called hypo by photographers) is used to stop development of exposed film. Thiosulfate converts undeveloped silver bromide grains in the film into water-soluble silver thiosulfate complexes that can be removed when the film is washed.
See these Web sites for more detail on the chemistry of photography:
|A laboratory exercise showing how photographic developers work. Includes a section on toning for iron, copper, and sepia.|
|The composition and preparation of film paper, and developing chemicals is described.|
Author: Fred Senese email@example.com
Copyright © 1997-2010 by Fred Senese
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Last Revised 08/17/15.URL: http://antoine.frostburg.edu/chem/senese/101/consumer/faq/print-photographers-hypo.shtml