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This International Standard specifies test methods for the determination of residual thiosulfate and other related chemicals in processed photographic materials.

This International Standard applies to silver halide/gelatin products that have been processed with a final thiosulfate fixing bath and a water wash. This International Standard does not apply to stabilised black-and-white products, thermally processed films, or instant-type products. The procedures given in this International Standard measure residual thiosulfate, and the silver densitometric method measures residual related polythionate materials as well. Measurements carried out by the procedures in this International Standard may, within the limitations stated in annexes A and B, correlate with the image stabilities of processed photographs.

Film or plates with photographic-sensitive layers on both sides, or with a photographic sensitive layer on one side and a gelatin backing layer on the reverse side, may contain approximately twice as much thiosulfate after processing as samples having a coating on one side only. This situation will be true for materials for which residual thiosulfate is determined by the iodine-amylose or methylene blue procedures.

The iodine-amylose can be used with fibre-based paper, resin-coated paper, films and plates. It is the method to be used with films and papers containing incorporated developing agents.

The methylene blue method can be used with fibre-based paper, resin-coated paper, films and plates but not with films and paper containing incorporated developing agents.

The silver sulfide densitometric method measures thiosulfates, polythionates and all other residual chemicals in a processed product that react with silver ion to form a silver “stain” under the conditions of the test.

A tabulated summary of methods, scope, etc. is given in annex B.