Patent GB-470074-A (GB)
Title: Production of coloured photographic images by development
IPC: G03C7/30
Filed: 1936-02-06
Abstract: 470,074. Colour photography. MURRAY, H. D., and SPENCER, D. A. Feb. 6, 1936, No. 3644. [Class 98 (ii)] Two latent photographic images situated one above another in one or more silver halide emulsion layers attached to one side of a support are developed by applying in succession to one surface of the layer or layers and without any intermediate fixing operation two developers, one to develop the image nearer the surface and the other being a colour developer adapted to develop preferentially the image remote from the surface by the addition to the developer of a soluble thiosulphate, cyanide, iodide or a like soluble substance which reduces the concentration of free silver ions in the emulsion. The substances used are referred to as forming highly insoluble compounds or complex salts with silver salts. Preferably both developers are colour developers and in one form of the invention the two images are first developed by a normal black and white developer, and are then fixed, washed, bleached and redeveloped with two colour developers, one adapted to develop in colour the image nearer to the surface and the other adapted to colour develop preferentially the image remote from the surface. The latent images are preferably produced by exposing the layer or layers from opposite sides. The images may correspond to different colour sensations and the developers may include colour-forming substances adapted to develop images in the appropriate colours. In one method a lightsensitive emulsion, preferably dyed yellow, is exposed first from the front side of the emulsion and then through the support and then developed with a colour developing solution to which has been added a high proportion of an inorganic salt to prevent excessive swelling of the emulsion. After development of the surface image and washing there is used a second colour developer containing a soluble thiosulphate or iodide to develop the image in the depths of the emulsion. The images are then bleached, fixed and washed. In another example rapid development of the surface image is obtained by an energetic developer loaded with inorganic salts or glycerine to delay penetration into the emulsion. The image nearer the base is developed by a colour developer of the kind already described and the surface silver image then converted into a coloured image by toning or by the method described in Specification 377,706. In another example a blue-sensitive bromide emulsion stained with Tartrazine is exposed from the back through a negative and from the front through another negative. After development with a metol developer and washing to remove the Tartrazine the dried emulsion is bleached with potassium ferricyanide and chloride and then the top image developed with diethyl-para-phenylene-diamine hydrochloride and p-nitro-phenyl-aceto-nitrile together with added sodium sulphate to delay penetration ; after rinsing in acetic acid the bottom image is developed with diethyl-para-phenylenediamine hydrochloride and p-nitro-aceto-acetanilide developer containing sodium thiosulphate. After washing and removal of the silver with Farmer's reducer further washing and drying gives a magenta image overlying a yellow one. The invention is also applicable to the processing of " double coated " kinematograph films. For example one side of the film has a blue-sensitive emulsion coating containing a water-soluble yellow dye, the other side has a panchromatic emulsion layer or one sensitized to red and infra-red light, which may contain an inert blue dyestuff removable during the treatment. Printing from three colour separation negatives is carried out by printing, (a) the red filter record by blue light on to the blue-sensitive layer, (b) the blue filter record on the second emulsion by infra-red light through the bluesensitive emulsion and the support (c) the green filter record is printed by blue or red light on to the surface of the second emulsion, the development of this latter image being performed by the already-described developer for images in the depth of the emulsion. Four colour-separation images in two pairs, each in one layer of a double-coated film may be obtained.