GB510523A - Production of subtractive multi-colour photographic pictures - Google Patents

Abstract

510,523. Photographic toning processes. GROVES, W. W. (I. G. Farbenindustrie Akt.- Ges.). Jan. 31, 1938, No. 2984. [Class 98 (ii)] In a process for the production of subtractive multi-colour photographic pictures in a multilayer photographic material, iri which a ferrocyanide blue image is produced in one layer and one or more coloured images are produced by the silver dystuff bleaching-out process in another layer or layers, and in which the ferrocyanide blue image is weakened by the bath used for bleaching, the colour density of the ferrocyanide blue image is restored by subjecting the photographic material to treatment with a concentrated suphuric acid-potassium bichromate bath after the bleaching operation. In the example given a film has two layers on one side, the lower being purple and sensitized to red while the upper is yellow and sensitized to green, and one layer on the other side not sensitized and comprising. a yellow dyestuff capable of being washed out by the developer. In the lower of the two layers the image is copied by red light'from the green component image developed to a positive while in the upper of the . two layers the blue component image developed to a positive is copied by green light, and in the single layer the red component image developed to a negative is copied by the blue light. The film is then developed and fixed, toned in blue on the side carrying the red component by floating on one of the known blue toning baths producing a ferrocyanide blue image, fixed and then bleached by the usual dyestuff bleaching-out bath. The film is then run through a bath comprising 1 litre of water, 5 grams of potassium bichromate and 10 c.cs. of concentrated sulphuric acid. The film is then washed or in case any silver halide is present, owing to the presence of halogen in the bleaching bath, it is again fixed and then washed and dried. Specification 454,088 is referred to.