Patent GB-553377-A (GB)
Title: Improvements in or relating to the production of three-coloured cinematographic films
IPC: G03C7/26
Filed: 1941-11-14
Abstract: 553,377. Colour photography. COOTE, J. H. Nov. 14, 1941, No. 14655. Drawings to Specification. [Class 98 (ii)] A multicolour image comprises, in different strata of a single silver halide emulsion layer provided with a gelatin or like supercoating, a magenta image of a nickel compound of a dialkylglyoxime and an insoluble metal salt image mordanted with a basic yellow dye, and in the supercoating a blue-green ferro-ferricyanide image produced by cyanotype sensitization. It is produced by printing in different strata of the emulsion layer images developed to silver from blue and green colour separation negatives, converting the green record print to the magenta dialkyglyoxime image, converting the blue record print to the yellow mordant dye image, sensitizing the supercoating with a cyanotype sensitizer, and printing and developing the blue-green image therein from a red separation negative or positive. In an example, an ordinary film comprising a transparent base, bearing a silver halide emulsion layer incorporating a fugitive yellow dye such as tartrazine is exposed through the base to the green-record negative. The latent image, which is restricted by the yellow dye to the lowermost stratum, is developed with an ordinary metolhydroquinone developer and washed, whereafter the silver image is bleached to a combination of nickel and silver ferrocyanides in a bath confaining potassium ferricyanide and a soluble nickel salt. The film is washed and dried, exposed from the front to the blue-record negative, and the latent image is developed in the upper stratum only by means of a metol-hydroquinone developer loaded as with sodium sulphate to control its rate of penetration. After treatment in a stop bath, an acid fixing bath, and washing, the second image is converted into a mordant for basic dye, e.g. silver iodide or other halide, or a waterinsoluble salt of copper, chromium or iron, washed, dyed yellow as with auramine, thioflavine, or chrysoidin, and washed free from excess of dye. The first image is now toned magenta in an alkaline bath containing dimethylglyoxime, followed by washing and drying. The supercoating is sensitized with a cyanotype sensitizer which is concentrated and of high speed to limit its penetration, e.g. one containing ferric ammonium citrate (or ferric chloride), potassium ferricyanide, and oxalic (or tartaric) acid, exposed to the red-record negative, and the latent image is developed blue-green with water. In another example, the film is exposed through the base to the blue-record negative, developed but not fixed, exposed from the front to the green-record negative, developed and fixed ; the second image is bleached in the aforementioned nickel bath loaded, however, with glycerine or sodium sulphate to limit its action to that image only ; the first image is dye-toned yellow; the bleached second image is toned magenta in the dimethylglyoxime bath ; and thereafter the blue-green image is produced in the supercoating by the cyanotype process as before. The method of producing the blue-green image may in either case be varied by sensitizing with a bath containing ferric chloride and oxalic acid, and developing, after exposure to the negative, with a substance yielding a ferro-ferricyanide, e.g. a potassium ferricyanide bath. A further variation consists in exposing to a red-record positive, and developing in a bath of potassium ferrocyanide. A filter dye less fugitive than tartrazine, e.g. Brilliant Yellow, may be used in the emulsion layer if this is thin, so that the dye is not completely eliminated in the first washing, and the residue assists in restricting the depth of exposure when producing the second image. Formulae for the various baths are given. The invention may be used in the production of still photographs or kinematograph films.