GB622772A - Improvements in or relating to coloured colloid layers - Google Patents

Abstract

622,772. Colour photography. WALLER, C., DICKINSON, H. O., and ILFORD, Ltd. April 3, 1947, No. 9144. [Classes 97 (i) and 98 (ii)] Coloured colloid layers are produced by treating a substantially colourless colloid layer, containing colloidal silver selenide in such small quantities that substantially no colour is imparted to the colloid layer, with a solution of a reducing agent in the presence of another silver compound and a solvent therefor. When forming part of a photographic material the colloid layers may contain a silver compound such as silver halide or may be adjacent to a silver halide emulsion layer. Reduction is effected as by a photographic developer in the presence of a solvent for the silver compound such as potassium thiocyanate or sodium sulphite, the colour produced being yellow to red, or brown. Layers containing the colloidal silver selenide may be made by adding to a colloid such as gelatine or other protein, polyvinyl alcohol or hydrophilic cellulose derivatives, a selenium compound such as selenourea, allyl selenourea and selenosulphates and a silver salt such as the nitrate or halide and heating for a short period. The layers are of particular value as filter layers in colour photography, and a multilayer material may comprise a transparent support carrying red-, green- and bluesensitive silver halide emulsion layers with two interposed layers according to the invention, that between the green- and blue-sensitive layers being coloured yellow with a fugitive dyestuff or by inclusion of yellow colloidal silver. The material may also include subbing, antihalation and antiabrasion layers and an ultraviolet absorbing layer. The exposed material is developed in a developer containing a silver solvent when the two interposed layers both become coloured. The emulsion layers may be selectively processed to colour by reversal colour development with the aid of the filter layers by successive blue light exposures on each side of the material and by rendering the middle emulsion layer developable by exposure to very bright light or X-rays or by fogging with sodium arsenite, hydrogen peroxide or guanidine thiocyanate. The first formed negative silver images may be removed by acid dichromate or permanganate before re-exposure, the silver selenide being unaffected by this treatment. On treating the final product with Farmer's reducer, all the silver and silver salts are removed, to leave a colour picture. Example 1 describes a three-emulsion film and its development to colour, the colour formers being contained in the final developers, and example 2 a film and process in which the redsensitive layer itself contains a colour former, the details being the same as those of examples 1 and 2 of Specification 595,582, except that the sulphides of that Specification are replaced by selenides. Specification 505,099 also is referred to.