GB665150A - Improvements in or relating to colour photography - Google Patents

Abstract

665,150. Colour photography. ILFORD, Ltd. March 20, 1950 [March 23, 1949], No. 7945/49. Class 98 (ii). A masked colour record suitable for printing improved colour copies of opposite sense is made by exposing a multilayer film having red, green and blue-sensitive silver halide layers containing colour formers, the blue-sensitive layer being either outermost or else next to a support, colour developing followed if desired by a vigorous bleach and white development, reexposing part of the residual silver halide, developing in a non-colour-forming developer, converting at least part of the then remaining silver halide to silver sulphide, and removing silver and any still remaining silver halide. The position and contrast of the sulphide masking, image may be controlled by fully reexposing any layer in which a mask is not required, by fully re-exposing but incompletely re-developing 'a layer in which a mask is required or by partially re-exposing and fully redeveloping such layer. Conversion of silver halide to silver sulphide may be effected by use of sodium sulphide or alkaline thiourea solution and the silver sulphide may be converted by ion interchange to cadmium, arsenic or antimony sulphide. In example (1) a specified film of conventional true colour negative type is re-exposed in the top, blue-sensitive layer by blue light whose action is restricted thereto by an underlying yellow colloidal silver filter layer, to provide masks in the red and green-sensitive layers, and it is suggested that a high contrast positive film should be used for printing this. Example (2) describes reexposure of the red-sensitive layer with red light in addition to the blue light re-exposure, resulting in a mask in the green-sensitive layer only. Specifications 475,784, 475,786, 544,645 and 550,994 are referred to.