Patent GB-540975-A (GB)
Title: Colour photography and kinematography
IPC: G03C7/26
Filed: 1940-03-27
Abstract: 540,975. Colour photography and kinematography. TULL, A. G. March 27, 1940, No. 5494. [Class 98 (ii)] Sensitive material for recording or copying comprises a base coated with silver halide emulsion, different layers or strata of which are differently colour-sensitive, the layer or stratum nearest the base being blue sensitive and diffusely coloured with a yellow dye capable of local destruction under control of a silver image formed therein, and the other strator or layers being substantially colourless. The processing may be direct or by reversal, to natural or complementary colours; -and the images formed in the uncoloured layers may be chemically toned, e.g. to Prussian Blue and uranium ferrocyanide, the red of the latter, if desired, being changed or reinforced by dye-toning. A material described consists of a celluloid support, blue-sensitive yellowdyed emulsion, colourless green-sensitized emulsion, green-absorbing filter (if desired), colourless red-sensitized emulsion, and anti-halation layer (if desired), exposure thereof being made through the support. The first processing step is to develop to silver in an ordinary developer. If a positive is to be produced by reversal, the first developer contains a proportion of a silver-halide solvent, e.g. potassium thiocyanate and thereafter the residual silver halide is converted,, e.g. as in Specification 540,970, into a silver ferrocyanide or other intermediate which permits the images in the upper two layers to be selectively toned, e.g. in a mixed bath containing a ferric salt and uranium salt, the top image to Prussian Blue and the middle image to uranium ferrocyanide, as described in Specification 540,971. The thiourea-containing bath used to effect the conversion of the halide into a complex may be acidified as with sulphuric acid, and may also contain hydroquinone, so that it simultaneously discharges the yellow dye from the silver-containing parts of the bottom layer. Silver and any residual silver halide are finally removed as with Farmer's Reducer. Copies may be made, e.g. on similar material by the same process. The material may be processed to negatives in colours complementary to those of the original, and positives may be printed, e.g. on similar material by exposure through the support of the copy material, using white light or light of different colours in succession. In processing the negative, the silver images first developed are converted into silver ferrocyanide or other intermediate as in a bath of potassium ferrocyanide and ammonia. The top two layers are then subjected to a controlled toning operation in a mixed bath, e.g. as described in Specification 540,971 and referred to above ; or such toning 'agents may be included in the bleaching bath. The negative image in the pre-dyed layer may be produced at a stage in the processing in which the image in the layer exists as silver by treatment with a bath which destroys the dye at the places where silver is not present, e.g. one containing calcium hypochlorite and acetic acid. As before, the uranium ferrocyanide image in the middle layer may be converted into a dye-toned image. The final step is the removal of silver and any remaining silver salts as with Farmer's Reducer. Specifications 540,976, 540,977, 540,979 also are referred to.