GB732691A - Colour photographic process - Google Patents

Abstract

732,691. Colour photographic process. GILBERT, W., ILLSLEY, C. R., and IMPERIAL CHEMICAL INDUSTRIES, Ltd. Nov. 2, 1953 [Nov. 19, 1952], No. 29202/52. Drawings to Specification. Class 98 (2). A layer containing a mixture of at least two separately prepared gelatino-silver halide emulsions of different speeds, the speed of the fastest being at least 8 times the speed of the slowest, and containing also a colour former, is exposed and colour developed to produce a colour image of much higher density than that of the mean of the two emulsions, which mean would result from a corresponding mixed layer in black and white procedure. A chosen film speed may thus be attained by use of lower than the calculated proportion of the faster and more coarse-grained emulsion, leading to better resolution and greater clarity of the layer and, in multilayer work, of underlying layers. Any or all of the layers of a conventional multilayer element may be of the mixed emulsions. Development may be direct or by reversal and colour-correcting masks may be provided in the layers as by use of coloured colour formers as of Specification 673,091, diazo treatment of Specifications 645,170 and 652,953, styryl dye procedure of Specification 651,059, or black and white methods. One or more fast emulsions may be mixed with one or more slow emulsions and the colour former, and if desired water, surface-active agents, sensitizers or other adjuvants added. Example 1 details the composition of a red sensitized-cyan colour former emulsion mixture of 100 parts emulsion of speed 90 and 900 parts emulsion of relative speed 1, exposure of a layer of this to red light from a coloured object, treatment in a colour developer containing ethylene-diamine-tetra-acetic acid, hydroxylamine hydrochloride, sodium carbonate and sulphite, potassium bromide and 2-methyl- 4-N: N-diethylaminoaniline, bleaching and fixing. A graph from results of exposure of the fast and the slow emulsions and of the mixture thereof to a red stop wedge shows that the mixture will record a higher relative brightness range than either of the separate emulsions and a higher speed than the calculated mixture. Example 2 describes, similarly, a green sensitized-magenta colour former mixture of 450 parts emulsion of speed 60 with 550 parts emulsion of relative speed 1; and example 3 a multilayer material comprising the layers of examples 1 and 2 overcoated with a blue sensitive-yellow colour former mixture of equal parts of emulsions of relative speeds 8 to 1 and processing thereof to a multi-colour negative.