Patent GB-518477-A (GB)
Title: Method of producing photographic multicolour images
IPC: G03C7/28
Filed: 1938-07-21
Abstract: 518,477. Colour photograpby. GASPAR, B. July 21, 1938, No. 21655. [Class 98 (ii)] A multi-colour printing prototype is produced by processing an exposed and developed multilayer taking materialcomprising three differently light-sensitive layers, the front layer being undyed during the exposure, each of the other two layers containing an image-forming dye of which one is yellow, these dyes being destroyed locally where silver is present after the exposure and a dye-image being formed in the front layer from an infra-red absorbing dye. The multicolour master images produced are such that the part images consist of dyes of widely separated spectral absorption thus permitting the use of printing lights from widely separated spectral regions. Thus, the taking material may be processed to a master-image from which the part-image in the uppermost layer may be printed with infra-red rays, from which a second part-image -may be printed with light from the extreme short-wave part of the visible spectrum or with ultra-violet rays and from which the third part-image may be printed with light of intermediate wave-length, widely separated from at least one of the other wave-. lengths.' The infra -red absorbing dyes may be of the 'basic cyanine type or acid dyes capable of dyeing gelatin. In the use of basic cyanine dyes the front layer is hardened or tanned at the places of the original silver negatives and the dye is subsequently used for dyeing the unhardened parts of the gelatin and may be fixed therein by salt-formation or mordanting, Alternately the layer may be uniformly impregnated with a weakly coloured acid dye which serves to fix a basic dye of good infra-red absorption subsequently applied, whereby the front layer is dyed uniformly throughout and may be subjected like the other layers to local destruction of the acid dye followed by. washing out of the basic dye in accordance with the image. The originally dyed layers are preferably coloured with insoluble azo dyes such as the yellow dye, 4-acetylaminoaniline # p-cresol, and the magenta dye, 1-naphthylamine # 2-naphthol. In an example, a taking material comprising a colourless bluesensitive front layer, _ a green-sensitive second layer containing the above yellow dye and a red-sensitive third layer containing the above magenta dye is exposed, developed, fixed and subjected to local destruction of the dyes, e.g., as described in Specification 397,159. The material is then subjected to an aqueous bath containing potassium bichromate, potassium bromide. potassium ferricyanide, alum and acetic acid to 'convert the silver into silver bromide and to tan the gelatin in accordance with the image and the material is fixed, washed, dried and impregnated in a solution of 2 : 2<1>- diethylbenzthiatricarbocyanine p-toluenesulphonate, or other infra-red absorbing dye such as a suitable pentacarbocyanine, benzthiazole or quinoline dye which dyes the untanned gelatin in the front layer. 'The Provisional Specification refers also to the use of the dye destruction processes of Specification 395,718, 397,188 and 397,192.