Patent GB-595419-A (GB)
Title: Improvements in photographic processes
IPC: G03C7/24
Filed: 1945-01-31
Abstract: 595,419. Photographic processes. KODAK, Ltd., STEVENS, G. W. W., and KNOTT, E. B. Jan. 31, 1945, No. 2495. Addition to 581,772. [Class 98 (ii)] Photographic material comprising two emulsions, one of which (Type I) is a silver salt emulsion which forms the latent image mostly inside the silver salt grains and the other (Type II) a silver salt emulsion which form a surface latent image on the silver salt grains is selectively exposed to form latent images in both emulsions, and the latent images so formed are differentially developed to produce a reversed image in one emulsion and an ordinary image in the other emulsion. The material may be used in the production of a mask for colour correction. A glass support may be successively coated with a red-sensitized gelatino-silver chloride Type II emulsion and with a non-colour sensitized gelatino-silver halide Type I emulsion. The material is exposed to a multicoloured object or image through either a red and a blue filter successively or through a single filter transmitting red and blue. The Type I emulsion is of sufficiently high speed that the amount of blue light for its correct exposure is too small to have any practical effect on the Type II emulsion, hence the red exposure affects only the Type II emulsion and the blue only the Type I emulsion. The material is immersed in a surface developer and given a uniform blue re-exposure just sufficient to form a reversed latent image in the Type I emulsion, but insufficient to affect the Type II emulsion. The developer thus produces a negative red-record image in the Type II emulsion and a positive blue-record image in the Type I emulsion. The uniform exposure is made from the side remote from the Type II emulsion. The contrast of the positive image may be controlled by giving the uniform exposure at a suitable time after immersion in the surface developer. A positive image in the Type II emulsion and a negative image in the Type I emulsion may be produced by omitting the uniform re-exposure when developing the negative latent image in the Type II emulsion, thus not developing the Type I emulsion, dissolving out this negative image with a bath not destroying the redsensitivity of the Type II emulsion or the internal image of the Type I emulsion, giving a uniform red light re-exposure to the material preferably on the side remote from the Type I emulsion and immersing in an " internal " developer. When the Type I emulsion is more stable to fogging developers than is the Type II emulsion (e.g. when the Type II emulsion is silver chloride), the red light re-exposure is omitted so that only the Type I emulsion develops in the " internal " developer, and then the material is developed with a fogging developer which rapidly develops the residual positive silver halide image in' the Type II emulsion without affecting the residual silver halide in the Type I emulsion. In a further modification, the material is treated after exposure in a surface developer to develop only the Type II emulsion, the silver produced is removed, a negative image is developed in the Type I emulsion with an " internal ' developer, the Type I emulsion treated with a solution preventing the formation of a surface latent image, and the residual silver halide of the Type II emulsion given a uniform re-exposure (e.g. to blue) and developed in a surface developer. In alternative materials, the Type I emulsion may have a relatively low speed in the blue to blue-green and be dye-sensitized to red, and the Type II emulsion may have a relatively high blue to blue-green speed. The Type I emulsion may be non-colour-sensitized and the Type II emulsion green-sensitized. A yellow filter layer may be provided between the two emulsion layers. The material may be used to record selectively coloured parts of a multicolour record, e.g. blue lines in a map with blue, red, magenta and black lines. In an example, glass is coated successively with a contrasty, low blue speed gelatino silver chloride Type II emulsion red sensitized with 3 : 31-dimethyl-9-ethyl-4 : 5 : 4<1> : 51-dibenzthiacarbocyanine iodide and with a gelatino silver bromiodide Type I emulsion having high blue to blue-green speed and little or no green or red sensitivity. The material is exposed to a map composed of blue, red, green and black lines first through a red filter and then through a blue filter, the second exposure being just sufficient to expose the Type I, but not the Type II emulsion. After development in a surface developer, the material is given a uniform exposure through a blue filter and development continued. Only the record of the blue lines was substantially clear in the resulting negative and positive images, and by printing a positive print of the original blue lines is obtained. Where black lines cross blue lines in the original, gaps occur in the blue lines on the final print. Specification 581,773 is referred to.