Patent GB-654124-A (GB)
Title: Improvements in or relating to colour photography
Inventor: ROBINSON RICHARD ROBERT
IPC: G03C7/18
Filed: 1948-07-06
Abstract: 654,124. Colour photography. ILFORD, Ltd. July 6, 1948, No. 18192. Drawings to Specification. [Class 98 (ii)] A " false coloured " photographic multilayer material comprises a support carrying a blue-sensitive silver halide emulsion layer (A) which contains a colour-former yielding a dye which, though transmitting light of two primary colours, yet absorbs light of those two colours to a considerable extent, a next adjacent green or red sensitive silver halide emulsion layer (B) which contains a colour-former yielding a dye which, though transmitting light of two primary colours, yet absorbs light of at least one of those two colours to a considerable extent, and a next adjacent red or green sensitive silver halide emulsion layer (C) which contains a colourformer yielding a dye which transmits light of two primary colours, the layer (A) being the emulsion layer most remote from the support, the colour-former in layer (C) yielding a yellow dye and the colour-formers in layers (A) and (B) yielding magenta and cyan dyes or vice versa, in which photographic material the gradations of the said photographic emulsions are dependent on the silver and colour-former coating weights and are such that when the said multi-layer material is exposed and colourdeveloped so that, by means of exhaustion of colour developer as it diffuses through the outer exposed emulsion layer towards the inner emulsion layer, image areas in layer (B) exposed to any particular level and adjacent to image areas in layer (A) have a density less than image areas in layer (B) which have been exposed to the same level but which are not so adjacent, and so that image areas in layer (C) exposed to any particular level and adjacent to image areas in layer (B) or layer (A) have a density less than image areas in layer (C) which have been exposed to the same level but which are not so adjacent, the record obtained of a neutral object is substantially neutral. The material may be exposed to a coloured object. or to a set of negative separation records in silver using appropriately coloured lights, and colour developed so as to produce this result. More particularly the invention comprises a " negative positive " process of colour photography in which a coloured negative is copied on to a similar positive material and processed to produce a true colour record of an object, and this process is illustrated diagrammatically in a drawing. The sensitivities of the positive material and the absorptions of the dyes in the negative may extend outside the visible region without impairing the process. Example 1 describes production of two films, a negative on clear film base at silver coating weights of 20 mg. per square dm. and a positive on white film base at silver coating weights of 10 mg. per square dm., each carrying the same assembly of layers : (a) upon the support a silver bromide emulsion green sensitized with 3,31-9-triethyl 5,51-diphenyl oxacarbocyanine bromide and containing the yellow colour coupler 4-stearoylamidobenzoylacet-2,5 dicarboxyanilide at a concentration of 0.85 g. per g. of silver in the emulsion, (b) thin gelatin separating layer, (c) silver bromide emulsion red sensitized with the dye described in example 11 of Specification 544,645, and containing the cyan colour coupler 1-α-hydroxy-#-naphthoylamido- 2-methyl-stearylamino benzene-4-sulphonic acid at a concentration of 0.4 g. per g. of silver in the emulsion, (d) colloidal silver filter layer, (e) blue sensitive silver bromide emulsion containing the magenta colour-coupler 1-(m-sulphop-phenoxy phenyl)-3-heptadecyl-5-pyrazolone, sodium salt at a concentration of 0.3 g. per g. of silver in the emulsion, (f) non-stress gelatin layer. The negative film was exposed in a camera, developed in a specified metol-quinol developer, fixed, bleached, washed, fully reexposed and colour developed for 16 minutes in a solution of diethyl-p-phenylene diamine hydrochloride 0.5 g., sodium sulphite 6 g., sodium carbonate 30 g. per litre, the low proportion of the first named, together with the absence of potassium bromide favouring the required developer exhaustion effect ; rebleached, fixed, washed, dried, and printed on to the positive film by three successive additive exposures using specified colour filters, and the positive developed similarly to produce a corrected colour print. A table summarizing colour densities obtained by measurement from the final positive as result of exposure of the negative to six coloured light sources and white and neutral grey is provided. Example 2 describes a pair of films and processing for them similar to those of example 1, but using the red-green-blue sensitivity sequences. Specifications 475,784 and 475,786 also are referred to.