GB501000A - Process of colour photography - Google Patents

Abstract

501,000. Colour photography; photographic developing processes. KODAK, Ltd. May 10, 1937, No. 26469/38. Convention date, May 9, 1936. Divided out of 500,826. [Class 98 (ii)] Relates to a process of producing colour developed reversed images in a three-layer photographic element whose upper layer is not specially colour sensitized and which contains colour sensitizers in the middle and bottom layers which are stable to photographic developing baths and to mild silver oxdizing baths. In one form the first latent images are developed to silver and the silver removed, then the reversed silver halide image in the middle layer is selectively made developable by exposure to coloured light and developed to colour, then the reversed silver halide image in the bottom layer is selectively made developable by exposure to coloured light from the back and developed to colour and finally the reversed silver halide image in the top layer is made developable by exposure to light and developed to colour. In another form the reversed silver halide image in the bottom layer is first selectively made developable by exposure to coloured light and developed to colour, then the reversed silver halide image in the middle layer is made developable by exposure to coloured light from the front and developed to colour and finally the reversed silver halide image in the top layer is made developable by exposure to light and developed to colour. In order to avoid the effect of local under-exposure in the lower layers, all the layers are first saturated with developing agent in high concentration and are then treated with weak alkali to effect development. Alternatively a concentrated developing solution is allowed to diffuse into all the layers at as low a temperature as it is possible to employ without alteration in composition of the solution and the development process started or accelerated by warming the layers to room. temperature or above. The residual silver halide may be converted in one or more layers to silver chloride, in a line state of subdivision as described in Specification 501,003. Suitable colour sensitizers are : (a) for extreme orangered and red, 4: 4<1>-dichloro-2 : 2<1> : 8-triethylthiacarbocyanine chloride ; (b) for red, 2 : 2<1>- dimethyl-8-ethyl-3 : 4 : 3<1> : 4<1>-dibenzthiacarbocyanine iodide; (c) for yellow-green, 2 : 1<1>- diethyl-3 : 4-benzthia-2<1>-cyanine iodide. Specifications 427,518, 427,520, 454,498, 454,499, and 454,622 also are referred to.