Patent GB-521888-A (GB)
Title: Production of coloured pictures
IPC: G03C7/26
Filed: 1938-10-22
Abstract: 521,888. Colour photography. SCHINZEL, K., and SCHINZEL, L. Oct. 22. 1938, No. 23022/39. Convention date, Oct. 22, 1937. Divided out of 521,746. [Class 98 (ii)] In an exposed three - colour photographic material having on a single support three differentially colour-sensitized silver halide emulsions, each of which contains a water insoluble ,organic derivative of a leuco dye such as a leuco vat dye ester or ester salt and preferably an indigosol, vat dye. colour component images are produced in the respective emulsions from the water insoluble organic compounds contained therein by a process which includes the step of developing a silver halide image in each of the emulsions or of intensifying a silver image in each of the emulsions by means of a physical developer containing hydroquinone or the like and also containing silver nitrate or a mercury salt which deposits the metal or a compound thereof on the image while simultaneously oxidizing the leuco derivative to form the dye image on the developed or intensified image. The silver halide image may be residual silver halide remaining after development of a silver image, which may be removed before the physical development of the residual silver halide. The silver image intensified may be that remaining after development and fixing of the original latent image. The physical developer may contain an inorganic acid, and may comprise a 1 to 3 per cent. solution of hydroquinone or its halogen substitution products or metol or p-aminophenol acidified with sulphuric acid and containing silver nitrate or mercury salts. In reversal, a long second exposure is necessary. Three-layer material containing colourless or yellow dye derivatives, preferably insoluble or non-diffusing salts of leuco sulphuric acid ester with organic bases not split by dilute sodium carbonate, sodium hydroxide. or ammonia, may be used. The organic bases are preferably easily destroyed by oxidation. Numerous suitable dye derivatives are referred to, and the. organic bases may be yellow dyes such as auramine, thioflavine T, trypaflavine, or other acridinium dye, or may be diphenylguanidine, triphenylguanidine. aristochin, or di- or poly-cinchonine. A yellow dye derivative may be used for either of the three emulsions. When certain dye derivatives are used. the residue must be washed out. With kinematographic films. especially if actinic rays are filtered from the projection light, the residual dve derivatives may be left. Reversal may be effected by reducing and removing the first-formed image dyes and oxidizing the residual dye derivatives. High - molecular dye derivatives mav be employed in the form of water-soluble alkali or ammonium salts or as insoluble salts with organic bases. The residual dye derivatives may be hydrolysed in the absence of air and washed out. Highly-polymeric azo indigosols may be employed and both the azo indigo and the residual azo indigosol split by reducing agents before removal of the latter. The dye derivatives may be absorbed on the silver halide grains. Colloidal insoluble salts of leuco esters formed with high-molecular bases may be coagulated on the silver halide grains. The emulsion may be saturated with excess of precipitant for the sensitizer and filter dye. Betaine hydrochloride may be used as the acid to prevent attack on the gelatin. In the case of triphenylmethane and azotriphenylmethane dyes a phosphotungstate may be added during the reaction to prevent diffusion. Specifications 500,826, 503,752, 512,559, 520,173 and 523,296 are referred to. The Specification as open to inspection under Sect. 91 comprises also the subject-matter of Specifications 516,536, 516,719, 521,746, 521,833, 521,834, 521,835. 521,836 and 521,837. This subjectmatter does not appear in the Specification as accepted.