Patent GB-511462-A (GB)
Title: Improvements in or relating to colour photography
IPC: G03C7/14
Filed: 1938-07-05
Abstract: 511,462. Colour photography. COMPAGNIE FRANCAISE POUR L'EXPLOITATION DES PROCEDES THOMSON-HOUSTON. July 5, 1938, No. 19947. Convention date, July 9, 1937. [Class 98 (ii)] In a process of obtaining photographs in colour starting from a lenticular film bearing a nlurality of developed and fixed primary colour component images in black and white, an additional light-sensitive layer is applied to the emulsion layer of the film, and one of the colour component images is printed thereon and coloured, for example by toning, and the steps of applying an additional light sensitive layer, printing a primary image thereon, and colouring is repeated until all the primary images have heen printed and coloured. The original emulsion layer may be re-sensitized for example by chromium salts and one of the primary images therein illuminated and coloured. The antihalation layer may be sensitized and used as one of the additional layers. Two or more of the primary images may be successively printed and coloured in one additional layer. In an example, a layer of gelatin sensitized with a bichromate is attached to a processed lenticular film, the green component image is illuminated and the additional layer is treated in a bath containing Pinatype Red F. The additional layer may then be lightly tanned. Two further additional layers are then successively attached, the appropriate component images are illuminated and coloured with Pinatype Blue F and Pinatype Yellow F respectively. Owing to diffusion a subtractive effect is obtained. A transparent non-sensitive layer may be placed between the original emulsion and the first additional layer or the light source may be increased in size or moved to produce blurring. Brown images formed by chromium salts are removed in an acid bath and silver salts are moved either wholly or partially by a mixture of ferricyanide and thiosulphate. The processes employing light-sensitive diazo compounds, iron salts, and potassium permaganate may also be employed. In another example, an additive effect is obtained by avoiding diffusing, but using the colours of subtractive synthesis using suitable light sensitive compounds such as diazo compounds. The silver image is not removed and the additional layers may comprise collodion or regenerated cellulose layers sensitized with diazo compounds. Two primary images may be illuminated simultaneously and the colours of additive synthesis employed to colour the non-illuminated third images. In a further example light sensitive leuco bases in layers of collodion varnish, or salts of chromium, cobalt or cerium, or diazo-compounds such as diazosulphonates, are used as the sensitive materials to produce the coloured film either by additive or subtractive synthesis. In the latter case the original silver image is removed after processing. In a further example silver bromide or chloride layers may be used and the colour produced by toning or mordanting. All or two of the additional layers may be dispensed with by resensitization of the original emulsion: A water-insoluble varnish such as collodion may be applied to the original emulsion and between the additional layers may be applied to preserve the original and secondary images from the successive treatments applied to the additional layers. Slightly permeable intermediate layers, for example layers of gelatine hardened by alum, may also be employed. The exposure of the successive layers is effected with light to which the previous coloured images are transparent. Layers containing light-sensitive leuco-bases or diazo-compounds are particularly sensitive to colours complementary to those produced in the material. Ultra-violet light can be used for exposure. Bichromatic layers may be treated with a solution of an ultra-violet absorbing compound such as aesculin, which is absorbed only in the non-hardened non-coloured parts. The sound track may be protected from the final removal of the silver by varnishing. The lenticulations may be removed by rolling. The coloured images may be observed by reflection. Specifications 487,685 and 488,398 are referred to.