Formation of silver sulfide in the photographic image during fixation.

A photo.graphic s!h:er im~ge is m ade ,Permanent (fix ed) aft~r development by bathing It 111 a solutIOn contall1lng thIOsulfate whICh forms a soluble tlllosuifate complex with the res idual silver halide.Some of the sil ver in the image is sulfided by the thiosulfate durin g ~xat io~.The p~rpose of this s tudy was to d etermine the a mount of sulfiding of the silver III t he Image dunng fi xatIOn of film and paper.The amo unt of the silver reacting depends on the type of t he ligh t-sensitive layer.Also, during bleaching, the residual thiosulfate in the film or paper r eacts with silver in a potassium dichromate-s ulfuric acid bleach bath to form silver sulfide.For one p ap er , it was shown that the amo unt of silver sulfide which was formed in the bleach bath increased with the increase of the concentration of the residual thiosuifate in the paper.A procedure was developed for t he reduction of silver s ulfid e in an e mulsion layer to silver so t hat the silver sulfid e may be determined in terms of the optical density of the s ilv l' dep osit.The use of hypo eliminators was investigated an d a test procedure was found for testing the effectiveness of hypo eliminators.A smaH amoun t of potassium iodide added to t he fi xing bath was found effec t iv e in preventing mos t of the s ulfidin g of the silver image during fi xation.