500,796. Colour photography. KODAK, Ltd. May 10, 1937, No. 37123/38. Convention date, May 9, 1936. Divided out of 500,826. [Class 98 (ii)] In the processing of material containing silver salt colour nomponent images in three photographic silver halide emulsions on a single support, one or two of the images only are made. developable by treatment with fogging agents after colour development of the images in the other two emulsions or of Che image in the remaining emulsion. The material may comprise a top non-specifically coloured sensitized layer, a middle yellow and green or red and orange sensitized layer, and a bottom red or yellow and green sensitized layer. 4 : 4<1>- dichloro . 2: 2<1>: 8 - triethylthiacarbocyanine chloride sensitizes to the extreme orange red and the red, but not to the green and the yellow. The three layers may be on the same side of the support or the red or the yellowgreen sensitive emulsion can be on the opposite side of the support to the other two layers. The material may also comprise two layers, either on the same or opposite sides of the support, one being of the mixed emulsion type. Three-layer material with a bottom red and orange sensitized layer and a middle yellow and green sensitized layer is, after camera or printing exposure, developed with a neutral black developer such as ferrous oxalate, amidol, or diamido-o-cresol, or with organic developers in sodium carbonate solution. colour sensitivity is restored if necessary by treatment with an alkali sulphite or bisulphite. The material may be saturated in a strong solution of the developing agent and development effected with solutions of sodium carbonate, ammonia, alkali bicarbonate, borax, trisodium phosphate or sodium aminoacetate, or alternatively a concentrated developing solution may be allowed to diffuse into all the layers at a low temperature and development effected by warming. If the material has a yellow filter in the upper layer or between the upper and middle layers, the bottom layer is exposed to red light and developed blue-green, the upper layer exposed to blue light after removal of the silver and developed yellow, and the residual silver halido of the middle layer is rendered developable by treatment with a fogging agent, such as thiourea, thiosinamine, stannous chloride, arsenite, hypophosphite, thallous salt, triamidophenol or fogging dyes in the presence of heavy metal salts, and developed purple. The fogging agent may be added to the colour developer. All the silver is then removed. If the material has two filters, either both yellow or one yellow or one red or orange, the lower layer is first exposed to blue light. If the material has a colourless or yellow ultra-violet absorbing filter between the top and middle layers, the lower layer is re-exposed to red light and colour developed, the top layer exposed to ultra-violet light and developed yellow, and finally the middle layer is made developable with thiourea or other fogging agent and colour developed. Alternatively, the top layer is re-exposed to blue light and colour developed by controlled penetration of a colour developer, the bottom layer exposed to blue and colour developed, and the middle layer treated with a fogging agent and colour developed. If the material has two ultraviolet filters, the top and the bottom layers are successively exposed to ultra-violet light and colour developed and the middle layer rendered developable by treatment with thiourea or other fogging agent and colour developed. The silver is then removed. If the upper layer is of silver chloride, the lower layer is exposed to red light and developed blue-green, the top and middle layers simultaneously rendered developable by fogging agents such as thiourea or stannous salt, and the top and middle layers successively selectively colour developed. The silver chloride layer may be developed first, another layer rendered developable by exposure and colour developed, and the remaining layer rendered developable with a fogging agent and colour developed. In material with a non- specifically colour sensitized emulsion layer and a mixed emulsion layer of which one emulsion is silver chloride, and a yellow filter in the former layer or between the two layers, the blue-sensitive layer is re-exposed before or after removal of the initially developed silver and developed yellow, the mixed emulsion layer is rendered developable by a fogging agent, the silver chloride emulsion is developed purple or blue-green and the silver bromide emulsion developed blue-green or purple. In material having three layers on one side of the support of which the bottom one is tanned, the two top layers are developed to black, the top layer re-exposed to red or blue light, and colour developed. The middle layer is rendered developable by a fogging agent and colour developed. The lower layer is detanned, treated with a fogging agent and colour developed. Material having two yellow filters, two ultra-violet absorbing filters, or a yellow and an ultra-violet absorbing filter, the material may be developed to black, fixed, bleached to silver chloride or bromide. The two outer emulsions are successively exposed to blue or ultra-violet light and colour-developed, and then the middle layer is rendered developable with a fogging agent and colour developed. Silver and the filter dyes are removed. The ultra-violet absorbing filter need not be destroyed. In material in which the colour sensitizer of the middle layer resists development and oxidation, the middle layer, after general black development, is re-exposed to yenow or red light and colour developed, the other two layers-are treated with a fogging agent, the top layer is colour developed by controlled penetration of a colour developer, and finally the bottom layer is colour developed. Specifications 341,183, 440,032, 440,489, 447,092, 454,622, 499,185, 500,611, 500,719, 500,793, and 500,826 are referred to.