Verfahren zur Herstellung eines photographischen entwicklerhaltigen Umkehrmaterials

1,012,860. Direct positive photographic emulsions. ILFORD Ltd. July 28, 1964. [Aug 28, 1963] No. 34090/63. Heading G2C. A photographic material comprises, on a support, (1) a layer of direct positive fogged silver halide emulsion containing at least 95 mol per cent of silver chloride, and containing a desenting agent effective to sensitise the Herschel effect to produce direct positive characteristics, and (2) a separate layer of water-permeable colloid containing a developing agent. The layers may be contiguous or separated by a thin layer of water-permeable colloid. Suitable direct positive emulsions are described in Specifications 871,938, 873,937, 875,887, 905,237 and 907,367. The emulsions are preferably fogged with formaldehyde. Hydroquimone is the preferred developer. In the example a gelatino silver chloride emulsion was fogged with formaldehyde, neutralised with citric acid, desensitised with 1-(2-pyridyl)-2-(4-pyridyl)-ethylene bis-benzyl bromide; coated on to paper, dried and a gelatin solution containing hydroquinone applied; the material was then activated with alkali and stabilised, with an aqueous ethanolic solution of ammonium thiocyanate, sodium sulphite, sodium metabisulphite and 1-phenyl-5-mercaptotetrazole.