Patent GB-581772-A (GB)
Title: Improvements in photographic processes
IPC: G03C7/30
Filed: 1942-09-02
Abstract: 581,772. Photographic sensitive material for composite pictures ; colour and stereoscopic photography; kinematograph picture and sound films. KODAK, Ltd., KNOTT, E. B., and STEVENS, G. W. W. Sept. 2, 1942, No. 12422. [Class 98 (ii)] A sensitive material comprises on a single support two silver salt emulsions which can be selectively exposed of which, upon exposure, one forms a latent image mostly inside the grains (Type I), and the other forms a latent image on the surface of the grains (Type II). Images produced in such material may be processed by treating it first with a developer which will develop the surface image only, and then with a developer which will develop the internal image. The emulsions may be mixed, superimposed, or juxtaposed and the material may be used in the production of multi-colour images, combined picture and sound films, stereoscopic anaglyphs, or kinematograph films having two parallel ranks of images of different character. A further material comprises on a single support two sensitive silver salt emulsions, mixed, superimposed, or juxtaposed, one of each of the above-stated types, but of different gammas which may, for example, differ by at least 2.5, the lower gamma being not more than 1.8. This material is for use in multi-contrast work, e.g. for producing images of different contrasts from negatives of the same contrast, or images of the same contrast from negatives of different contrasts. Examples of emulsions of Type I are Burton's emulsion (Wall: "Photographic Emulsions," pp. 52, 53), and an ordinary silver iodobromide, emulsion which has been bathed in a bath containing potassium bichromate and sulphuric acid. The conditions which such an emulsion must satisfy in order to be useful in the invention are stated in the Specification. Emulsions of Type II comprise most gelatinosilver-halide emulsions ; on exposure they form both surface and internal latent images. In order that the mixed or superimposed emulsions may be selectively exposed, they may have different colour sensitivities, and where a not specially colour-sensitized emulsion is associated with a colour-sensitized emulsion, the blue sensitivity of the former should be high relatively to the blue sensitivity of the latter ; alternatively, where the emulsions are superimposed, they may be separated by a colour filter layer. Examples of developers which will develop surface images only are (I) one containing p-hydroxyphenylglycine and sodium carbonate, and (III) a metol-hydroquinone developer containing sodium sulphite, potassium bromide, and sodium carbonate. For developing internal images, (II) a similar metol - hydroquinone developer containing sodium carbonate or sodium hydroxide and also sodium thiosulphate may be used. In one example, for two-colour work, a not specially colour-sensitized silver bromide or iodobromide emulsion of Type I, mixed with an alcoholic solution of hydrolysed soft lac resin such as is described in Specification 511,180, is mixed with or overcoated upon a silver chloride emulsion of Type II sensitized to green with the dye 5-[(2-ethyl- 1(2)benzoxazolylidene) -ethylidene]-3-n-heptyl-1-phenyl-2-thiohydrantoin described in Specification 532,098, also mixed with said resin solution. Processing of this material after exposure consists in treating with an ordinary surface colour developer containing a colour coupler to yield a magenta image, to colour develop only the surface latent image in the Type II silver chloride emulsion, thereafter treating with an'internal-image developer containing a colour coupler yielding an orange image to develop the internal image in the other emulsion, and finally removing all silver and unused silver halide from the material. Another example of material for two-colour printing work comprises on one side of a support a process type emulsion which has been converted from Type II to Type I by treating it successively in a hardening bath, a solution of potassium bichromate and sulphuric acid, and a solution of sodium bicarbonate, and on the other side a minus-blue filter layer overcoated with an emulsion of Type II. In a further example, for three-colour work, in which selective processing of the emulsions is rendered possible partly owing to their selective exposure characteristics and partly by taking advantage of other known means, a red-sensitized silver bromide or iodobromide emulsion of Type II, an ordinary blue-sensitive silver bromide or iodobromide emulsion of Type I, and a greensensitized silver chloride emulsion of Type II are used ; and the three emulsions may be mixed, or coated in three superimposed layers, or in two superimposed layers in one of which two emulsions are mixed. After exposure, the silver chloride emulsion may be selectively developed by treating in a mildly-acting developer such as Formula VII of Specification 427,518 before the other two emulsions are separately developed in accordance with their types. Known controlled penetration means may alternatively be used to differentiate between two superimposed emulsion layers of the same type during the individual processing of the layers. In a particular three-colour twolayer material of this kind, one layer comprises a silver bromide or iodobromide emulsion of Type II sensitized to red as with 3 : 3<1>-dimethyl- 4 : 5 : 4<1> : 5-dibenzthiacarbocyanine iodide, and the other layer contains a mixture of a silver iodobromide emulsion of Type I sensitive only to blue, and a silver chloride emulsion of Type H sensitized to green with the dye mentioned in the two-colour example above. After processing the silver chloride emulsion as stated above, treatment of the remaining two emulsions is similar to that in the said example except that the latent image in the red-sensitive layer is developed in a surface developer containing a colour coupler yielding a blue-green image, and the internal latent image in the not specially colour-sensitized emulsion is developed in an internal-image developer containing a colour coupler yielding a yellow image. Material for multi-contrast work may comprise an emulsion of Type II giving low gradation in developer III above, and an emulsion of Type I giving a high gradation in developer II above ; and conditions to be satisfied by the threshold speeds and characteristic curves of these emulsions are indicated in the Specification. Such material may be printed with white light and the contrast of the image controlled in the processing procedure. In one example specified, low contrast results by developing with developer III above ; medium contrast by developing with developer II ; and high contrast by first treating in a mild oxidising bath which destroys the surface latent image in the Type II emulsion, and then developing in developer II above. Suitable mild oxidising .baths contain (a) potassium ferricyanide andpotassium bromide, or (b) potassium bichromate and sulphuric acid. It is possible also to process such material by first treating the whole material in a surface developer, and then treating it in an internal developer. Specifications 427,518, 500,611, 500,826, 540,444 and 541,510 also are referred to.