Abstract
The addition of sodium thio ulphate to the washing step before an acid-bleaching treatment re,ults in a reinforcement of the fog and of the surface latent image in the overexposure region. This intensification is shown by surface development after bleaching. Fog density rises initially. decreasing afterward., with increasing thiosulphate concentration. At the same time, overexposurc surface latent image shows intensification, which is ubstituted afterwards by a rever’al with respect 10 fog.A corresponding behaviour is reported when the overall treatment is carried out on grains which have been developed in both a surface developer and in a very diluted developer.These etrects have been studied in three commercial -ray emulsions for dinerent thio. ulphale concentrations.The results are interpreted in termS of initial adsorption and ulierior desorption of thiosulphate ions at the grain surface and at developed silver image, where the thiosulphate adsorbed gives rise to developable silver sulphide nuclei hen il11mer,ed in the acid-bleaching solution. We sugge,t lhal the same mechanism applies 10 the large crystallizcd silver specks which arc photolytically formed at the surface of the grains in lhe solarization and re-revcrsal regions.
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