GB658588A - - Google Patents

Abstract

658,588. Photographic silver halide emulsions. DU PONT DE NEMOURS & CO., E. I. June 17, 1949, No. 16205. Convention date, June 17, 1948. [Class 98 (ii)] A photographic developing-out emulsion comprises a silver halide dispersion in a hydrophilic colloid binder containing a small amount of a sulphur sensitizer and very small amounts of gold, palladium, and mercury, e.g. 0.0000723 to 0.000288 mol. per cent of gold, 0.000104 to 0.000975 mol. per cent of palladium, and 0.000108 to 0.000162 mol. per cent of mercury, based on the silver content of the emulsion. The sulphur sensitizer may be a sulphur compound naturally occurring in photographic gelatine or an added compound such as sodium thiosulphate or thiocyanate or allyl thiourea or isothiocyanate. The emulsion binder may be gelatine, agar-agar, a polyglycuronic acid, zein, collodion, a water-soluble cellulose derivative (e.g. substantially hydrolysed cellulose acetate, an alkali metal salt of a cellulose ester of a dicarboxylic acid such as phthalic acid, or a cellulose ester of a hydroxymonocarboxylic acid such as lactic or glycollic acid), polyvinyl alcohol, a partially hydrolysed polyvinyl acetate or an interpolymer thereof with an unsaturated compound such as styrene or maleic acid, or a water-soluble polyvinyl acetal. In examples, the relative speed, gamma, and fog values are given for a silver iodobromide emulsion sensitized with 3 : 3<SP>1</SP> - diethyl - 9 - methylthiocarbocyanine iodide and with and without various additions of sodium thiosulphate, chlorauric acid, palladium chloride, and mercuric chloride. In a further example, the additions (apart from sodium thiosulphate) are made to a silver iodobromide emulsion in gelatine containing naturally occurring sulphur sensitizers. Specifications 527,283, 542,703, 542,704, 551,659, 570,393, 602,158, 636,140, 636,234, and U.S.A. Specifications 2,059,642, 2,110,491, and 2,211,323 are referred to.