GB430991A - An improved method of producing coloured photographic materials - Google Patents

Abstract

430,991. Colour photography; colour filters. GASPAR, B., 38, Innsbrucker Strasse, Schoneberg, Berlin. Dec. 28, 1933, No. 36491. Convention date, Dec. 29, 1932. [Classes 97 (i) and 98 (ii)] Coloured photographic images or layers are produced by incorporating hydrazo substances or their derivatives in the photographic or image - bearing layer and subsequently converting them to dyestuff. The hydrazo compounds may be incorporated in the emulsions or in the layer after exposure, by bathing, or in the emulsion before application to the support. A finished silver image may be immersed in a solution of a hydrazo compound which is then converted diffusely into an azo dyestuff, the dyestuff being subsequently destroyed locally at the image or non-image positions, e.g. as described in Specifications 395,718, 397,159, 397,188, and 397,192. Alternatively, the dyestuff may be produced locally by converting the silver image into an oxidant, e.g. lead chromate ; or the hydrazo compound may be locally destroyed at the image points with slightly acidified thiocarbamide, the remaining hydrazo compound being subsequently converted to dyestuff. Multicolour photographs may be produced by combining particles of emulsion of different colour-sensitiveness with different hydrazo compounds in the manner of multicolour screen images, with or without filter dyestuffs ; or by the use of multi-layer material containing appropriate hydrazo compounds in the different layers. Specified hydrazo compounds are benzene hydrazo-alpha-naphthol, hydrazobiphenyl and hydrazoines. Insoluble salts of hydrazo compounds, e.g. hydrazo aryl, sulphonic acids with salts of nitrogenous organic bases may also be employed. Suitable oxidizing agents are ferric chloride and nitrous acid. Colour filters may be produced by treating the layer to form a diffuse silver image and converting this into a diffuse dyestuff deposit.