GB967036A - Photographic reversal process - Google Patents

Abstract

967,036. Photographic reversal processes; dye-bleach processes. CIBA Ltd. Dec. 19, 1962 [Dec. 20, 1961], No. 47950/62. Heading G2C. A reversed image is produced in a photographic silver halide material of which the halide is predominantly bromide by developing the exposed material to a silver image, converting the silver to silver chloride and selectively removing the latter in a thiosulphate bath without removing the unexposed silver bromide, removal of the silver bromide being prevented by treating the material with a heterocyclic mercaptan at any time after the primary development but not later than during the action of the thiosulphate. The silver bromide remaining is then converted into a silver image in known manner. The mercaptan may be 2-mercaptobenzthiasole or 2-mercapto-benzimidazole. They may be used in a separate bath after the stop bath, or in the stop bath or thiosulphate bath or both. The stop bath may comprise acetic acid and sodium acetate. The primary silver image may be converted into silver chloride in a copper nitrate/ hydrochloric acid bath or in a potassium ferricyanide/sodium chloride bath. The invention may be applied to the silver-dye bleach process by including a bleachable dye in the light-sensitive silver halide material. After the formation of the reversed silver image according to the invention, the dye is bleached imagewise and the excess remaining silver removed by conversion into silver chloride in a copper nitrate/hydrochloric acid bath and fixing. An example is given of the production of a multi-colour image by the silver dye-bleach process.