Patent GB-475655-A (GB)
Title: Improvements in or relating to colour photography
IPC: G03C7/26
Filed: 1936-05-23
Abstract: 475,655. Colour photography. POLLAK, L. O. A. May 23, 1936, No. 14596. Drawings to Specification. [Class 98 (ii)] A silver halide emulsion sensitive to part of the spectrum and formed from non-hardened or hot-water-soluble gelatine and containing colour-forming substances, is superposed, with or without intermediate filters, on one or more silver halide emulsion layers sensitive to other parts of the spectrum and formed from insoluble hardened gelatine. The colour-forming substances may be water-insoluble salts of the naphthol-, naphthalene-, naphthylamine-, or benzidine sulphonic or disulphonic-acids. After exposure, the element is desensitized, developed, fixed, washed, and bleached in a solution of copper sulphate, potassium bromide and chromic acid, thereby hardening the gelatine in the upper layer. After treating in hot water to form a wash-out-relief, the bleached image is converted to a dyestuff image by treatment with diazotized dianisidine. Alternatively, the diazo-compound may be in the emulsion, the image being obtained by use of an azo-coupling component. The other images may be mordanted by thiocarbamide and ammonium thiocyanate and dyed with a basic dyestuff, such as rhodamine B. In modifications, the first development may be effected with a tanning developer such as caustic alkaline pyrocatechin. The dyestuff-forming compound may be added to the hot water relief-forming bath. The images may be colour-developed or chemically toned as, for example, with vanadium salts. The non-hardened emulsion layer may contain dyestuff-precipitating agents such as barium carbonate, phosphotungstic acid, antimoniotungstic acid or silicotungstic acid. Leuco-dyestuffs and dyestuff-esters may be added to the emulsion and the oxidation and hot water baths combined. A film may comprise on one side of the support a yellow and green sensitized hardened emulsion, a filter layer, and a yellow and red sensitized non- hardened emulsion containing an insoluble azodyestuff coupling component such as aminonaphthol disulphonic acid H and on the other side a blue-sensitive hardened emulsion poor in silver. After exposure, the element is processed as above, and a blue-green dyestuff formed in the upper layer by diazotized dianisidine. After mordanting in a thiocarbamide, ammonium thiocyanate and acetic acid bath, the other two images are dye-toned bluish-red with rhodamine B. After drying, the twolayer side of the film is varnished, and the red dyestuff image is removed on the other side with acidified potassium permanganate solution. The film is washed, and. the bleached image dye-toned yellow with acridine-yellow or thioflavin T. A bipack element may comprise a two-layer film in contact with a single-layer film. The single-layer film may be dye-toned and registered on the two-layer film or may be used to transfer an image by imbibition on to the two-layer film. A positive film has three superimposed layers comprising a blue sensitive hardened silver bromide or chlorobromide emulsion containing a yellow filter, or having a yellow filter superimposed thereon, a hardened green or red sensitized emulsion, and a non- hardened red or green sensitized emulsion containing an azo-dyestuff coupling component or a dyestuffprecipitator. The negative is printed thereon through a yellow filter to produce latent images only in the upper two layers, which are developed in a tanning developer and treated in a hot water bath containing a diazo-coupler or a dyestuff. The images are bleached and dyed bluish-red with rhodamine B. The negative is again printed on the positive through a blue filter, and developed and toned yellow by a vanadium bath or colour-developed yellow. The remaining silver halide is dissolved out by fixing. The order of processing may be reversed. Multicolour screen negatives may be printed on such positive material or negatives according to the invention may be used in the preparation of positives by the imbibition process. The films may carry a sound track. Specifications 344,365, 353,819, and 430,823 are referred to.