Patent GB-485552-A (GB)
Title: Method of producing colour selection pictures from multicolour master images
IPC: G03C7/18
Filed: 1936-08-20
Abstract: 485,552. Printing colour record photographic images. GASPAR, 13. Aug. 20, 1936, Nos. 22927 /36 and 11085/37. Drawings to Specification. [Class 98 (ii)] To avoid the reproduction of unwanted images in printing the part images from a multicolour subtractive record, e.g. on multilayer material, with coloured light, the printing lights are chosen so that the ratio of the absorption of the printing light by the image to be reproduced to the absorption of the light by the undesired image is a maximum, or in the case of more than two images, the smallest of such ratios is a maximum. The printing light may be provided by a source emitting a line spectrum, for example suitable sources are arcs, sparks, discharges in rarefied gases, or lamps in which atomic line spectra are excited by heat, thermal emission, or optically as in resonance tubes. Alternatively, sources emitting band spectra may be used in conjunction with a filter. To avoid the difficulty of overlapping absorption of the dyes constituting the original image, images in which the concentration of the dyestuffs is unbalanced may be used, for example images in which the concentration of dye in the yellow image is considerably increased. Examples of the effect of printing with various sources of light, from images dyed with various dyes in balanced and unbalanced concentration are given in the Specification. The images may be developed to the same or different degrees of contrast. Separate part images may be produced or the printing performed on multilayer material. For example, a multicolour image comprising a blue component record coloured blue-green, a red component record coloured magenta, and a green component record coloured yellow is printed onto three layer material comprising a blue-sensitive layer coloured magenta, a layer sensitized with pinacyanol blue and coloured yellow, and a red-sensitive layer coloured blue-green. Printing is effected of the red record with thallium light, and the other two records with mercury and cadmium lights respectively. If the layers are superimposed on one side of the material and the lower layers separated by a hardened gelatin layer, different gamma values may be obtained in the three layers on development in a single developer. The silver images may be converted into dye images in known manner, e.g. by means of a bath of thiocarbamide and citric acid. In another example, material is used consisting of a colourless red-sensitive layer, a yellow green-sensitive layer, and a colourless blue-sensitive layer, nearest the support. After exposure through the support, developing, and fixing, the uppermost layer is dyed red, and the images in the two upper layers converted to dye images with a bath of acidified thiourea or potassium iodide. The image in the layer nearest the support is then converted into silver ferrocyanide and treated with ferric sulphate giving a Prussian-blue image. The blue picture is then printed with potassium or caesium light onto material sensitized with pinacyanol blue and the red and green partial pictures with cadmium and mercury lights respectively. Further examples are given. A geometrical method of determining the gamma values to which each of the prints is to be developed according to the density of the dyestuffs in the master images is also given in the Specification.