It has been repeatedly suggested that chemical sensitization by sulfur compounds depends not only on the formation of silver sulfide, but on its rearrangement on the grain surface to form sensitivity centers. The most direct evidence for this is that there is no sensitization on addition of soluble sulfide to the emulsion which forms silver sulfide, but, on heating the emulsion with the sulfide for a longer time and a higher temperature than those used for thiosulfate sensitization, equivalent sensitization can be obtained. Stabilizers such as 6-methyl-4-hydroxy-l,3,3a,7-tetraazaindene (TAI) , which stop photographic sensitization, do not stop the chemical reaction of silver sulfide formation. It has now been demonstrated that when TAI is added to the emulsion after formation of silver sulfide from a soluble sulfide, it prevents the sensitization on heating, and hence must stop rearrangement, l-phenyl-5-mercaptotetrazole retards sensitization when added after the sulfide is formed, but appears to act mainly as an antifoggant during development. Increasing the pAg also retarded the rate of sensitization but did not stop rearrangement.

Library of Congress Subject Headings

Photographic emulsions; Photographic sensitometry

Publication Date


Document Type


Department, Program, or Center

School of Photographic Arts and Sciences (CIAS)


Carroll, Burt


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