Patent GB-547519-A (GB)
Title: Improvements in and relating to colour correction in colour photography
IPC: G03C7/18
Filed: 1940-11-21
Abstract: 547,519. Colour photography. KODAK, Ltd. (Eastman Kodak Co.). Nov. 21, 1940, No. 16737. [Class 98 (ii)] A colour photographic record is provided with an integral colour-correcting mask in a material having two or more emulsions on a single support, of which one is a light-sensitive unexposed silver salt emulsion, and another is a uniformlydevelopable silver salt emulsion, one being superimposed upon the other, by producing one colour record image of a coloured original by exposure of the said light-sensitive emulsion, simultaneously developing this image and the silver salt in the uniformly-developable emulsion, fixing out the undeveloped silver salt, uniformly oxidising the silver formed in the uniformlydevelopable emulsion only to a light-sensitive silver salt, colour-sensitizing it if desired, and producing a second latent colour record image of the same coloured original to serve as the mask, by exposure of this light-sensitive silver salt. The second image may be developed to silver and the undeveloped silver salt again fixed out. The residual silver salt in the initially lightsensitive emulsion may be colour developed after developing the first latent image in the emulsion to silver, in which case the second latent image in the other layer may also be colour developed, e.g. to neutral grey, or be developed to silver. When there are more than two emulsions for the colour record components of the original, there may be two uniformly-developable silver salt emulsion layers, each intended to contain a different masking image; or two different masking images may be produced in one layer. The invention is illustrated as applied to the production of a multicolour record with an integral mask in a multilayer film comprising three colour sensitive emulsion layers for the colour component images, preferably all on the same side of the support, and an ordinary emulsion layer coated on top for the masking image, this layer being fogged by light or chemically before or after coating. There may be a yellow filter to protect the green and red sensitive layers from blue light. The emulsions may be of silver bromide, chloride, or chloro-bromide. After exposure in a camera or printer, the images are developed to negative silver, e.g. in a metolhydroquinone developer (formula specified), the top layer being at the same time developed to give a uniform silver deposit. The film is then colour developed, e.g. as described in Specification 507,841 to produce colour component images from the undeveloped silver halide in the three colour sensitive layers. The uniform silver deposit in the top layer is converted to silver halide by a controlled bleaching operation, e.g. in an aqueous bath containing quinone, potassium bromide, sulphuric acid, ethyl alcohol, and ethylene glycol, whereafter the silver in the lower layers is removed as by acidified potassium bichromate solution. The top layer is sensitized, e.g. to red light as in an aqueous-alcoholic bath containing pinacyanol, pyridine and benztriazole, and the film is exposed through the support to red light so that the red transmission of all the lower image layers is impressed on the top layer, and this is then developed to produce a silver masking image of lower maximum density and preferably also of lower gamma than the subtractive colour records. The film is finally fixed, washed, and dried. If desired, the top layer may be sensitized for regions of the spectrum other than red, the exposure light in making the masking image being altered to suit the sensitization; in particular it may be sensitized for two of the colouraspect regions instead of only one. Instead of a silver masking image, a neutral grey dye masking image may be produced, either by colour development using a mixture of colour-couplers or p-benzyl phenol as colour coupler as in Specification 527,332; or a silver masking image may be toned as to silver sulphide, or with platinum. Instead of developing the colour records to positives, they may be developed to negatives, the colour sensitive emulsions in this case containing appropriate colour couplers to yield coloured negative images in the first development; or they may be processed to false colours as in Specifications 475,784 and 475,786. Specifications 427,518, 447,092, 454,498, 501,661. 512,608, 516,514, 516,816, 517,416, 537,864, 541,298 and 541,589 also are referred to.