Patent GB-736228-A (GB)
Title: Improvements in mixed grain colour photography
IPC: G03C7/30
Filed: 1952-10-24
Abstract: 736,228. Mixed grain colour photography. KODAK, Ltd. (Eastman Kodak Co., Carroll, B. H., and Hanson, W. T.). Oct. 21, 1953 [Oct. 24, 1952], No. 26770/52. Addition to 702,200. Class 98 (2). A method of producing a multi-coloured photographic record of a multi-coloured object or image by a reversal process which couples features of the main parent Specification with features of Specification 540,444, comprises the following steps: (a) exposing to coloured light from the multi-coloured object or image or from colour separation records thereof, a photographic light-sensitive material containing in one or two layers, three sets of silver halide grains, the sets having sensitizing maximum in the blue, green and red regions of the spectrum respectively, such maxima in the green and red, and optionally, the blue, regions being obtained by the use of sensitizing dyes, and the dye for sensitizing the set of grains at a maxima in the red region being one which in the concentration employed sensitizes at the desired sensitizing maximum but in a lower concentration sensitizes at a different sensitizing maximum, and the sets being all either silver bromide or bromiodide, the inherent blue speed of the set of grains having a sensitizing maximum in the blue being at least 10 times the inherent blue speed of the set of grains having a sensitizing maximum in the green and at least 10 times the inherent blue speed of the set of grains having a sensitizing maximum in the red, and the exposure being through a filter transmitting light of a colour to which the printing speed of the set of grains having a sensitizing maximum in the blue is substantially thesame as the printing speeds of the other two sets of grains; (b) developing all the sets of grains in a black and white developer to form negative silver images therein; (c) re-exposing the material uniformly with light in a wave-band which includes the said desired sensitizing maximum in the red but excludes the blue and green sensitizing maxima and also excludes the said different sensitizing maximum; (d) colour developing the set of grains thereby exposed; (e) re-exposing the material uniformly with light in a wave-band which includes the said green sensitizing maximum but which excludes the said blue sensitizing maximum; (f) colour developing the set of grains thereby exposed; (g) re-exposing the material uniformly with light in a wave-band containing the said blue sensitizing maximum; (h) colour developing the set of grains thereby exposed; and (i) subsequently removing developed silver from the layer thereby leaving positive dye images in the material forming the multi-coloured photographic record. The dye sensitizing the set of grains for recording green may, similarly, sensitize at a desired maximum in the green region and also at a (second) different maximum, and in this case the re-exposing light of step (e) excludes also this second different maximum. In the two layer material grains for the blue region are usually coated as a separate layer over a mixed layer of the other two sets of grains. Specifications 532,098, 702,255, 722,231 and 722,237 are referred to.