The Removal of Hypo and Silver Salts from Photographic Materials as Affected by the Composition of the Processing Solutions

During processing, if photographic materials are insufficiently fixed and washed, the silver thiosulfates and sodium thiosulfate retained may result in staining of the non-image areas and fading of the image during subsequent storage. In the case of films and plates the thiosulfates may be removed completely if a judicious choice of hardening and fixing baths is made and if the most effective washing technique is employed but, with prints, traces of hypo are invariably retained which can be removed by subsequent treatment in a peroxide-ammonia solution. — Several factors contribute to the retention of sodium and silver thiosulfates and the extent of this retention was measured by careful determination of the residual thiosulfate and silver in the processed material. The hardening agent, potassium alum, used in hardening baths and fixing baths caused the greatest retention while chrome alum had little effect. The accumulation of silver during exhaustion of the fixing bath resulted in retention of silver thiosulfates. — The removal of sodium and silver thiosulfates was aided by (1) use of a second fixing bath to remove silver and (if non-hardening) to assist removal of hypo, (2) an increase in the pH of the fixing bath preferably above the isoelectric point of gelatin, (3) hardening prior to fixation as compared to hardening during or after fixation, (4) raising the temperature of the wash water, (5) increasing the pH of the wash water or by the use of a dilute ammonia solution near the end of the washing process. These treatments were less effective with photographic papers because of the high retention of thiosulfates by the paper base and the baryta coating. Processing recommendations to insure permanency during (a) archival and (b) normal periods of storage are given.

Print ISSN

0097-5834

Published

1943-07

Content type

Original Research

DOI

10.5594/J09840