Patent GB-560373-A (GB)
Title: Method of producing photographic color separation images
IPC: D06M15/53
Filed: 1942-03-04
Abstract: 560,373. Colour photography. GASPAR, B. March 4, 1942, No. 2848. Convention date, Jan. 24, 1941. Drawings to Specification. [Class 98 (ii)] A colour separation record is produced from a multilayer material containing latent colour record images, e.g. the two-layer element of a three-colour bipack or a three-layer material, by developing all the images to silver, converting said silver to a silver salt having substantially the same optical properties as the residual silver halide in the layers and having substantially no sensitivity to the light and substantially no reactivity to the developer used in the further processing, selectively exposing the residual silver halide in one of the layers, developing it, and printing the resulting reversed image on to a separate layer sensitive to the printing light used. A second colour separation record may then be produced by converting the silver of the already-printed image to a silver salt of the above-defined character, selectively exposing the residual silver halide in another of the layers, developing it and printing the resulting reversed image on to another sensitive layer as before. When the material has more than two sensitive layers, the procedure may be repeated for making a third separation record. In a modified process, exemplified in the production of three separation records from a three-layer material, but applicable also in processing a two-layer material, the latent image in the top layer only is developed to silver with a rapid developer, and printed on to a separate sensitive layer, the remaining images are developed to silver, the silver in all three layers is converted to a silver salt of the above-defined character, whereafter the remaining two separation records are made successively by the above-described procedure of selective exposure, development and printing, with an intermediate conversion step. The material used may include yellow and red filter layers. The method is illustrated by three examples in which the silver conversion baths may be ferricyanide-iodide yielding silver iodide, or cupric bromide yielding silver bromide ; and the sensitivity of the layers after the conversion step may be restored as with a sodium sulphite bath containing sodium hydroxide or ammonia, or with a bath of ammonia only. The selective reversal exposures are made with light affecting only the layer to be reversed ; and the printing exposures are made with light, e.g. infra red, which does not affect the silver salts in the multilayer material, except in the case of the final printing step, which may be made with white light after fixing out the silver salts from the whole film. A formula is given for a rapid metol-hydroquinone developer containing also methyl' alcohol, sodium sulphite, sodium hydroxide, and potassium bromide ; and reference is made to a 1 per cent acetic acid stop bath, to cryptocyanine and a benzthiotricarbocyanine as infrared sensitizers, to pinacyanol as a red sensitizer, to thiopseudocyanine as a green sensitizer, to the calcium salt of the dye Xylenwalkgelb G as a yellow filter, and to the Panared filter described in Specification 496,559.