GB506359A - Improvements in the production of subtractive colour pictures - Google Patents

Abstract

506,359. Colour photography. L. G. FARBENINDUSTRIE AKT.-GES. Nov. 26, 1937, No. 32690. Convention date, Dec. 1. 1936. [Class 98 (ii)] In the production of subtractive colour pictures by the silver colour bleaching-out process, a. silver picture is superimposed on a component colour picture without an exposure to an original additional to the exposure required for producing the colour picture and is composed of material originating wholly or in part from the silver halide emulsion required for producing the silver picture through whose intermediary the component colour picture is formed. The development of exposed photographiC material may be interrupted by an acetic acid stop bath, followed by destruction of the dyestuff or the stop bath can be dispensed with if an acid dye-destruction bath is used. The silver is dissolved by a bichromate and sulphuric acid or an ironammonium alum and sulphuric acid bath, the remaining silver halide is subjected to diffuse illumination, preferably preceded by treatment with bisulphite to increase the sensitivity, and developed. or blackened without illumination by treatment with sodium sulphide. The first developer may contain a silver halide solvent such as ammonia, an alkali sulphocyanide, or an organic amine. Part of the silver halide may be dissolved before the second development by treatment with sodium thiosulphate or another solvent, or the first development may be separated into two stages the first part of the development being conducted with a dilute developer, and the second part, effected after the dye-destruction, being effected with a powerful developer containing a silver halide solvent. The silver picture can be reduced or intensified subsequently. A lenticular bipack may be printed on to u silver coulour bleaching film having on one side of the support a layer dyed blue-green and un the other side purple and yellow layers. The film is developed, treated in a dye-destruction bath comprising hydrochloric acid, metol, and potassium bromide, further developed in a developing bath of different composition, treated with the iron-ammonium alum and sulphuric acid bath to remove silver, treated with a sodium bisulphite bath containing 2 to 3 per cent of thiosulphate, diffusely illuminated, developed and fixed.