Patent GB-486424-A (GB)
Title: Improvements in the production of multi-colour photographic pictures
IPC: G03C7/26
Filed: 1936-10-28
Abstract: 486,424. Colour photography. GROVES, W. W. (I. G. Farbenindustrie Akt.-Ges.) Oct. 28, 1936, No. 29305. [Class 98 (ii)] A process for producing component colour record pictures by means of a photographic material comprising several superimposed, preferably differently sensitized, light sensitive layers, and containing in intermediate layers or in the light sensitive layers, filter substances which selectively absorb the visible, ultra-violet or infra-red regions of the spectrum, comprises subjecting the material to two exposures, the second exposure being by lights which act on one side of the material and are absorbed by the light absorbing substances contained in the material. In a bipack arrangement, the front film has a lower layer not specially sensitized separated from a layer sensitive to green by a yellow filter layer, e.g. Fulling Yellow G or Thioflavine S both of which are not essentially attacked by the treatment baths. The rear film carries a layer sensitive to red. The positions of red and green sensitive layers may be reversed. After the first development of the front film, the silver is removed, e.g. by bichromate and sulphuric acid. The second exposure is conducted separately for the two layers by means of blue light, or, in the case where the sensitizing dyestuff has been destroyed, by white light. The one layer that has been exposed is blackened, and copied onto an auxiliary film which is developed by reversal. After removing the silver in the front film, the other layer is exposed and developed. Three component pictures are thus obtained. Instead of using an auxiliary film, the layers may be separately exposed and colour developed to red and green respectively. The two components are separated by the yellow filter layer and the red dyestuff image can therefore be copied with green light and the green image with red light. A layer of the front film may alternatively be developed or toned so that it is opaque to infra-red light with which it is then copied. When the components are to be obtained as negatives, the silver obtained after first developing and fixing is reconverted to silver halide and given the controlled second exposure. A bipack in which the green and red components are produced on the rear film may also be used, a red, orange, or yellow filter layer between the two component layers enabling the selective exposures to be made. A four colour copy may be made by arranging on the front film a panchromatic layer and above this a filter layer which absorbs ultraviolet, the second exposure of the front film being to ultra-violet light. In a modification in which colour pictures are obtained directly, a material having three sensitive layers has two intermediate filter layers containing substances transparent to all rays except ultraviolet and infra-red, that between the blue and green sensitive layers also containing a yellow dyestuff, and that between the green and red sensitive layers containing a red dyestuff. The dyestuffs are adapted to be destroyed at the first development but the substances which absorb ultra-violet and infrared withstand these baths. In the second exposure the outer layers are exposed to either ultra-violet or infra-red and the middle layer to blue light. The film is then subjected to either colour development or toning. In all cases the last component picture may be produced without a second exposure by chemical conversion or toning or dyeing of the silver halide. The process is applicable also to multilaver material combined with either a colour screen or a lenticular screen. Specification 461,006 is referred to.