GB1282778A - Direct-positive silver halide photographic process - Google Patents

Abstract

1282778 Direct-positive silver halide photographic process EASTMAN KODAK CO 5 Sept 1969 [9 Sept 1968] 44081/69 Heading G2C A method of making a positive photographic record comprises imagewise exposing a sensitive photographic material comprising a layer of a direct-positive silver halide emulsion which contains an electron-accepting compound and a BSI compound (as defined in U. K. Patent Specification 1186718), and of which the silver halide comprises at least 50 mole per cent of silver chloride and of which the grains have internal centres which promote the deposition of photo-lytic silver and surface-fogged outer shells or regions and surfacedeveloping the exposed layer using a polyhydroxybenzene developing agent. The developer may be in the material, in a solution or in a layer on a separate support which is brought into contact with the material. Surface development may be effected with a 'lith' developer (i.e. one capable of giving infectious development) which may contain a carbonyl bisulphite-amine condensation product with at least 0À075 mole of excess free amine per litre and a dihydroxybenzene developing agent. The internal centres which promote the deposition of photo-lytic silver may be produced by chemical sensitization e.g. with potassium chloroiridite, or by fogging by exposure to low or high intensity light. The grains may be surface fogged by chemically sensitizing to fog or by exposure to high intensity light. In the examples the grains are surface fogged by heating with thiourea dioxide and potassium chloroaurate. The electron acceptor may be 1, 1'-diethyl-2, 2'- cyanine chloride treated with N-bromosuccinimide or 1, 3-diethyl-1'-methyl-2'-phenylimidazo- [4, 5-b] quinoxalino-3'-indolocarbocyanine iodide. The BSI compound used in the examples is 3- carboxymethyl-5-[(3-methyl-2(3)-thiazolinylidene)- isopropylidenej rhodanine.