Patent GB-468560-A (GB)
Title: Improvements in and relating to colour photography
IPC: G03C7/28
Filed: 1935-10-08
Abstract: 468,560. Colour photography. KODAK, Ltd., and CROWTHER, R. E. Oct. 8, 1935, No. 27765. [Class 98 (ii)] Sensitive material for colour photography consists of three or more emulsion layers sensitized to different colours together covering substantially the whole visible spectrum, and arranged on one or both sides of a support, at least the layer first hit by incident light being uncoloured and containing no colour forming component and at least the layer last hit being dyed with a dye capable of being decoloured or removed at the image or non- image places. Suitable material comprises a support of cellulose acetate coated with three layers on one side, the outer layer being uncoloured and blue-sensitive, the intermediate layer being uncoloured and sensitized for green with 1 : 2<1>-diethyl-5: 6-benzthiapseudocyanine iodide, and the bottom layer being dyed with colloidally dispersed indigo and sensitized for red with 8 - methyl-2 : 21-diethyl- 3 : 4 : 3<1> : 4<1 >- dibenzthiacarbocyanine bromide. Clear gelatin layers which may be dyed with yellow and magenta dyes may be interposed between the emulsion. layers. The emulsion layers may be thin and the upper layers may be more dilute in silver halide, and contain emulsions of finer grain than the bottom layer. The bottom layer may also be dyed with a dye transparent to red light and convertible to a blue-green colour, e.g. Niagara Blue G, Alternatively, the sensitizing of the lower layers may be interchanged, the bottom layer being in this case dyed with Algol Pink BBK and the filter layer above it being bluegreen. After exposure, all the images are developed in an elon-hydroquinone developer and the dye in the bottom layer destroyed at the image or non-image parts by treatment with oxidizing agents, e.g. chromic acid, quinone or potassium permanganate, or reducing agents, e.g. sodium formaldehyde sulphoxylate. The images in the upper layers may be processed to colour by the methods described in Specifications 376,838, 427,516, 427,518, 427,520, 453,233, 454,498, 454,499, 458,664, and 458,665. Where reversal is needed, a bleach bath for the silver images may comprise potassium bichromate and sulphuric acid. The film is in this case redeveloped in an elon-hydroquinone developer, fixed, washed, bleached in a solution of glycerin, isopropyl alcohol, quinone, and hydrochloric acid, the action of which may be stopped by a bath of sodium bicarbonate, glycerin, and isopropyl alcohol and is processed to yellow and magenta as described in Specification 440,032. The silver is finally removed with a solution of potassium ferrocyanide, sodium carbonate, and sodium chloride. An alternative form of film is described having a fourth layer dyed with a neutral black dyed and panchromatically sensitized. This black layer also forms an antihalation layer. Further examples in which the middle layer is coloured with a magenta dye, e.g. Algol Pink BBK and in which the layers are coated on the support in reverse order are given in the Specification. Specifications 341,183, 378,885, 385,267, 444,198, 446,234, 447,748, and 456,279, also are referred to.