Patent GB-516514-A (GB)
Title: Improvements in and relating to the photographic reproduction of coloured objects
IPC: G03C7/18
Filed: 1938-03-29
Abstract: 516,514. Colour photography. KODAK Ltd. March 29, 1938, No. 9526. Convention date, March 31, 1937. Drawings to Specification. [Class 98 (ii)] In a method of producing a corrected colour component record of a multi-coloured object which comprises directly exposing to the object through a filter transmitting both the component colour to be recorded and the correcting component colour a sensitive element having two superimposed differently colour sensitized emulsions and in which the latent image of the colour component to be recorded is processed to a negative and the latent image of the other colour component is processed to a positive of lower gamma than the negative the following alternative elements are employed. The element may comprise two gelatine-silver bromide emulsions superimposed on the same side of the support and the latent images produced therein are first developed to silver without fixing. The upper silver image is bleached to silver chloride and removed, the remaining silver bromide is fogged, the silver bromide in the upper layer only is developed, and both layers are fixed. The element may also comprise a top silver bromide and a bottom silver chloride emulsion, or may be such that the positive image is in the form of a colouring matter, for example produced in the dye destruction process. Three examples of the methods are described. In (1) A plate or film is coated with an emulsion layer sensitized to green light by 2 : 1<1>-diethyl-3: 4<1>-benzthio- 2'-cyanine iodide, a thin layer of gelatin and a layer of low contrast emulsion sensitized to red with 2: 2' diethyloxadicarbocyanine iodide. It is exposed through a yellow filter, developed and washed. The upper layer is bleached in a bath of glycerine, isopropyl alcohol, quinone and hydrochloric acid, time control being used and the action stopped by a bisulphite, isopropyl alcohol-glycerine bath. The silver chloride is then removed by means of sodium sulphite containing silver bromide, the plate fogged and the upper layer developed by controlled diffusion, in a bath containing hydroxyhydroquinone, paraphenylene diamine, sodium sulphite and triethylamine. The layers are thus fixed and washed to give a combination from which a magenta print-' ing plate is made. In (2), the lower layer is a silver chloride emulsion and after controlled bleaching as in (1) the plate is.fixed with sodium sulphite containing silver bromide, and the remaining silver bromide in the upper layer developed to a positive image by a standard developer containing monomethyl p-aminophenol sulphate, hydroquinone &c. In (3), a film is coated with an emulsion dyed yellow and sensitive to green, a plain gelatin layer and a blue sensitive emulsion; after exposure, development and fixing, it is treated in an acid solution of thiourea which bleaches the dye at the silver image. The element may then be printed with blue light to give a corrected positive. Alternatively the dye may be Vat yellow R and bleached by alkaline sodium stannite. Specifications 427,516, 427,517, 427,518, 427,520, 454,498, 454,499, 477,524 and 501,661 are referred to. The Specification as open to inspection under Sect. 91 comprises also a method in which the positive is produced on a solarising emulsion and a method in which emulsion layer is not specifically colour-sensitized and the other is green-sensitized, 'the positive being produced in this latter layer by reversal. This subjectmatter does not appear in the Specification as accepted.