GB160137A - Improved process for treating and dyeing photographic images and products obtained thereby - Google Patents

Abstract

160,137. Kelley, W. van D. March 11, 1921. Toning; colour photography.-In a process for obtaining colour transparencies by bleaching the silver image and subsequently dyeing it, the silver image is bleached in a bath that will transform the silver into a compound which is insensitive and not redevelopable by a developer, and then dyed in an acid or azo dye bath, which is mordanted only at the places in situ with the original silver. The image film may be first hardened by a formalin bath. The bleaching bath contains a copper or chromium salt or both. A bath instanced contains potassium bichromate, potassium bromide, copper sulphate, and hydrochloric or acetic acid. The image may then be treated in an acid fixing bath of hypo and sodium metabisulphite, or this may be done after dyeing. Acid or azo dyestuffs instanced include ponceaus, fast reds, acid fuschine and dyes such as used in wool dyeing, which give a choice of pure non- dichroic colours and a very transparent image. To brighten the colour a bath of ¢ per cent solution of sulphurous acid may be used. The process is used to obtain one or more of the component colour elements in a two or three colour photograph or kinematograph film, either in the same emulsion layer or on separate films.