Increasing the Washing Rate of Motion-Picture Films with Salt Solutions

Abstract

Adsorbed thiosulfates may be effectively eliminated from films by the use of salt solutions. The salts may be employed in the wash water, as when washing with sea water, or as a separate bath previous to washing. The rate of elimination is largely controlled by the anion, and monovalent anions such as acetate and chloride are less effective than polyvalent anions such as sulfate, sulfite, phosphate and citrate. — These principles are incorporated in the Kodak Hypo Clearing Agent (K.H.C.A.). The effectiveness of this bath is most striking with films fixed in strongly hardening alum fixing baths and washed in cold water. Under these conditions, it is not unusual for the hypo to be reduced to 1% of that left by washing alone for equal periods. The results obtained when this product is applied to machine, spray, and rewind processing of motion-picture films, microfilms and aerial films are described. In general, savings are effected in both the time required and the water consumed, while very low levels of residual hypo are attained.