Patent GB-500721-A (GB)
Title: Improvements in and relating to three-colour photography
IPC: G03C7/30
Filed: 1937-05-10
Abstract: 500,721. Colour photography. KODAK, Ltd. May 10, 1937, No. 36871 /38. Convention date, May 9, 1936. Divided out of 500,826. [Class 98 (ii)] Colour developed reversed images are pro. duced in material comprising three silver halide emulsion layers on a single support of which the upper layer is not specifically colour sensitized and of which the middle and bottom layers contain colour sensitizers, that in the bottom layer at least being resistant to the action of developing agents, and having a yellow filter colouring matter not destroyed by development in the upper layer or between the upper layer and the middle layer, by developing the first latent images to silver, exposing the residual silver salt image in the lowest layer only by coloured light to which the other layers are not sensitive and colour developing the lowest layer, exposing the residual silver salt in the upper layer by blue 'light and colour developing, and then colouring the reversed image in the middle layer, and removing the positive and negative silver from all the layers. The middle layer may be colour developed without exposure by a colour developer containing ammonia, caustic alkali, alcohol or acetone, preferably out of contact with the air. Alkaline, alcoholic, or acetonic solutions of leuco vat dyes may be used. The residues of the latent images in the other two layers are destroyed by mild oxidizing agents such as a mixture of potassium ferricyanide and ammonia. The residual silver halide of the middle layer may be made developable by exposure from above or, both sides to ultra-violet light or soft X-rays and colour developed. A residual silver bromide image in the middle layer may be converted to silver iodide or a complex salt thereof, which is then coloured purple by a mordanting dye and the latter made insoluble. The material may comprise a blue-violet sensitive upper layer, a yellow and green sensitive middle layer, and a red or infra red sensitive lower layer, or a blue-violet sensitive upper layer, a middle red and orange or infra-red sensitive layer and a lower yellow and green sensitive layer, or a red sensitive upper layer, a yellow green sensitive middle layer, and a bluesensitive lower layer. 4: 4<1>-dichloro-2 : 2<1> : 8- triethylthiacarbocyanine chloride very strongly sensitizes to the extreme orange-red and the red but not to 'yellow and green. A yellow filter may be arranged between the bluesensitive and middle yellow-green or redorange sensitive layers or in the blue-sensitive layer itself. 'Green or red-orange filter may be arranged between the middle and lower layers. A colourless or yellow layer may be arranged between the middle and lower layers. The whole material may be coloured yellow. The yellow filter colouring matter must be resistant to the first developer and the colour sensitizers to a neutral black developer and a weakly alkaline colour developer. Latent images produced in the material after camera or printing exposure are developed with a neutral black developer such as ferrous oxalate, amidol or diamido-o-cresol or with organic developers containing sodium carbonate. Colour sensitivity, may be restored by treatment with alkali sulphite or bisulphite. All three layers may be saturated in a strong solution of the developing agent and development effected in solutions of sodium carbonate, ammonia, alkali bicarbonate, borax, trisodium phosphate or sodium aminoacetate. A concentrated developing solution may be allowed to diffuse into all, the, layers at a low temperature and development effected by warming. The residual silver halide is then used for reversal development. Specifications 376,746, 427,518, 427,520, 454,498, 454,499, 454,622, 498,663, 498,876, 500,720, and 500,826 are referred to.