GB501002A - Process of and materials for colour photography - Google Patents

Abstract

501,002. Colour photography; photographic developing processes. KODAK, Ltd. May 10, 1937, No. 26471/38. Convention date May 9, 1936. Divided out of 500,826. [Class 98 (ii)] A process of producing colour developed reversed silver halide images in a three-layer photographic element, of the type in which the upper layer is not specially colour sensitized and the other layers are respectively sensitized to the red and green regions of the spectrum and in which the colour sensitizer in the middle layer is resistant to the action of photographic developing baths and mild silver-oxidizing baths and /or there is a yellow filter colouring matter in the upper layer or between the upper layer and the middle layer which is not destroyed by photographic developing baths or which is not destroyed by photographic developing baths and silver-oxidizing baths, is characterized in that the reduced silver is removed from all the layers before exposure of the residual silver halide image of the middle layer but after exposure and colour development of the residual silver halide image in the lower layer or in the lower layer and the upper layer. Suitable sensitizers for the middle layer are: (a) for red, 2 : 21 dimethyl-8-ethyl-3 : 4 : 31 4<1>-dibenzthiacarbocyanine iodide ; (b) for yellow-green, 2 : 1<1>- diethyl-3 : 4-benzthia-2<1>-cyanine iodide. If a very sharp blue image is desired the middle layer can be sensitized to the extreme orange red as well as the genuine red with 4: 4<1>-dichloro-2 : 2<1> : 8-triethylthiacarbocyanine chloride. Several examples of the process are described, in one of which development of the residual silver halide of the upper layer is effected by alkaline-solutions of the leucoforms of various yellow vat dyes preferably with exclusion of atmospheric oxygen to prevent fog as described in Specification 498,876, and in, another of which the middle layer is exposed from both sides to white, blue, or ultra-violet light or to soft X-rays and developed purple. 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. Specifications 427,517,427,520,454,498,454,499, 464,622, 500,717, and 500,793 also are referred to.