GB424563A - An improved method of producing photographic dyestuff images - Google Patents

Abstract

424,563. Colour photography. GASPAR, B., 38, Innsbruckerstrasse, Sch÷neberg, Berlin. June 23, 1933, No. 17963. Convention date, June 23, 1932. [Class 98 (ii)] Photographic dyestuff images are produced in photographic layers containing a silver image and a dyestuff by converting the silver image into a chemical compound which locally prevents or retards the action of a subsequently applied dyestuff destroying bath. As a modification, the silver image layer may contain a dyestuff-forming substance which is converted to a dyestuff simultaneously with the conversion of the silver image into the chemical resist. In an example, a dyed silver image layer is bleached in an aqueous bath of copper sulphate and hydrochloric acid, producing locally a reducing compound, and the dyestuff at the unprotected portions is then destroyed by oxidation, e.g. by permanganate of potash. Alternatively, the silver image may be converted to silver ferrocyanide or toned with selenium &c. In a further example, the silver image is converted to an oxidizing compound, e.g. to lead chromate by treatment with potassium ferricyanide, lead nitrate and potassium chromate, or to manganese peroxide by treatment with a manganese salt, the dyestuff being subsequently destroyed by a powerful reducing agent, e.g. sodium hydrosulphite. In an example involving dyestuff-forming substances, a silver image layer containing a leuco body is treated with copper halide, ferricyanide of potassium &c., to convert the leuco body into the dyestuff and simultaneously form the chemical resist. The invention is applicable to supports coated on both sides or provided with superposed layers ; also to multi-colour particle emulsions. Specifications 395,718 and 397,159 are referred to.