Patent GB-523179-A (GB)
Title: Photographic material for taking colour photographs
IPC: G03C7/18
Filed: 1938-12-28
Abstract: 523,179. Colour photography. GASPAR, B. Dec. 28, 1938, No. 37611. [Class 98 (ii)] In multilayer material comprising a support carrying at least two differently sensitized silver halide emulsion layers, one of the layers has uniformly distributed therein a colouring, substance capable of colouring the exposed and unexposed parts of the layer with two differently coloured dyes, the layer with the colouring substance in the form of only one dye having for light of a definite waveband the same absorption as the same layer with the substance completely converted into the other dye, the waveband being that of coloured light for which an imageforming dye in another is highly absorptive. In an example, the multilayer material has three emulsion layers on one side of a transparent. support. The bottom red-sensitive layer is dyed magenta with Direct Brilliant Pink B, the middle green-sensitive layer is dyed yellow with Chrysophenine G or Sinuslichtgelb R extra and the top blue-sensitive layer is undyed. After exposure and development the material is treated with a dye-destruction bath containing hydrochloric acid, potassium iodide and 2:3- diaminophenazine. A yellow positive image is obtained in the middle layer, while in the bottom layer a magenta positive image and a yellow negative image are obtained. The blue-sensitive layer may be on a separate support. On printing simultaneously or successively with green and blue printing lights, the green printing light prints only the magenta image on to a greensensitized layer, and the blue printing light prints the yellow positive image on to a blue sensitive layer, the yellow negative image in the bottom layer correcting for absorption in the magenta positive image. In another example the top bluesensitive layer is uncoloured, the middle greensensitive layer contains Benzo Light Yellow RL, and the bottom panchromatically sensitized layer contains Benzopurpurine 10B and the dyeformer Naphthol ASG. After exposure, development, fixing, and washing, the top layer is dyed with Pontamine Sky Blue 5BX, the film treated in a dye-destruction. bath comprising hydrochloric acid, sodium chloride, and 2-amino-3- hydroxyphenazinesulphonic acid, washed and bleached with acid cupric chloride solution, and a yellow image formed after re-exposure in the bottom layer of colour development. The silver is removed with Farmer's reducer. In a further example the top blue-sensitive layer contains carbonyl - bis - 8 - [4 - (4 - aminobenzamino) - benzamino] - naphthol - (1) disulphonic acid (3:6) and Indigosol 06B, a middle orthochromatic layer containing Benzo Light Yellow RL and a bottom panchromatic emulsion containing Hessisch Purple. After exposure, development, and fixing, the film is treated firstly with diazotized sulphanilic acid and sodium acetate to give a magenta dye in the front layer, secondly with a dye-destruction bath, and thirdly with an oxidizing solution as in example 6 of Specification 379,679 to form a blue-green dye locally in the front layer. The silver halide is removed by fixing. In place of Naphthol ASG leuco-esters of vat dyes may be used. The dye formers may also be converted into dyes by colour development or local azo-dye synthesis. Nitro-compounds may be first converted into an amino compound and then into the dye. A layer may contain an azo-coupling component and a nitro compound, the former being uniformly converted into a dye and locally destroyed while the nitro compound is simultaneously reduced to an amino compound, which can be used for local azo dye formation or colour development. The colour of the printing light is selected so that the dyes in the main and supplementary images have at the points of their maximum density the same absorption. Specification 492,672 also is referred to.