Light-sensitive photographic element and process using it

595,582. Colour photography. WALLER, C., DICKINSON, H. O., and ILFORD, Ltd. July 10, 1945, No. 17544. [Class 98 (ii)] Coloured colloid layers are produced by treating a substantially colourless colloid layer containing colloidal silver sulphide in such small quantity that substantially no colour is imparted thereby to the layer with a solution of a reducing agent in presence of another silver compound and a solvent therefor. When forming part of a photographic material the colloid layer 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, the colour produced being yellow to red or brown. Layers containin gthe colloidal silver sulphide may be produced from gelatin alone (which contains sulphur compounds) heated with silver nitrate or silver halide, or a sulphur compound, such as thiourea, allyl thiourea, thiosulphates, thiosemicarbazide or allylthiosemicarbazide may be added. A multilayer material may comprise a transparent support carrying red-, green- and blue-sensitive silver halide emulsion layers with two interposed layers according to the invention, that between the green and blue sensitive layers being dyed yellow with a decolourisable dye. The material may also include subbing, antihalation and anti-abrasion layers and an ultraviolet absorbing front layer. The exposed material is developed in a developer containing a silver solvent, when the two interposed layers become coloured and the yellow dye is decolourised. 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 eacli side of the material and by rendering the middle emulsion layer developable by exposure to 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, e.g. by acid dichromate or permanganate, before re-exposure, the colloidal silver sulphide being unaffected by this treatment, and the filter layers being coloured on re-development in the presence of a silver halide solvent. In example 1, material comprising a support (a), a red-sensitized silver iodobromide emulsion (b), a gelatin layer (c) containing colloidal silver sulphide and silver iodobromide, a green-sensitized silver iodobromide emu