Bleach-Enhanced Fog and Reduction Sensitization

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Abstract
Fogging of a silver halide emulsion by bathing in a dilute solution of a latent image bleach (bleach-enhanced fog, BEF) has been inve tigated on a series of bromide and iodobromide experimental emulsions. None of the emulsions showed B F in the absence of any deliberate sensitization or when only sulphur ensitized, but with the exception of a cubic bromide emulsion, all showed BEF when either reduction sensitized or sulphur-plus-reduction sensitized. Distribution of BEF between surface and interior depended on the same grain structure and sensitizing conditions that inOuenced latent image distribution. The presence of a desensitizing dye during bleaching prevented BEF. For surface BEF the solution that fogged the emulsionlaler destroyed the fog centres. It is proposed that BEF occurs when the concentration of oxidizing agent is sufficiently low 10 make thermal regression of a speck which has heen reduced in size 10 a single silver alom more probable than bleaching of the silver atom. Tili results in electron injection into the conductivity level and the formation of new fog centres.

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