GB187638A - Improvements in and relating to the formation and employment of a photographic record of lights and shades capable of use as a transfer printing plate - Google Patents

Abstract

187,638. Marks, E. C. R., (Daylight Film Corporation). April 18, 1921. Developing and after-treatment; photo-mechanical printing-surfaces; kinematograph picture films.-A process of forming a photographic record of lights and shades capable, of use as a transfer printing plate comprises hardening portions of exposed emulsion adjacent the light affected content of a photographic emulsion with an agent adapted to harden the emulsion by reaction with the light affected content of the emulsion and with a controlling agent for said hardening agent, the relative proportions of the hardening and controlling agents being such as to control selectively the area of influence of the hardening agent but to an extent less than the complete neutralisation of the hardening agent. The hardening under control may be effected during development, or the positive may be developed before the hardening is effected. In the first type of process a developer may be used containing pyrogallic acid as the hardening agent and sodium sulphite as the controlling agent, in approximately the proportions 1 : 2. In the second type of process the hardening is effected by the action of potassium bichromate in the presence of the silver image, the controlling agent being sulphuric or hydrochloric acid. The unhardened portions of the colloid remaining may be removed. The printing surface formed comprises a great number of photographically formed, extremely minute, individual protuberances, which are distributed and grouped irregularly so as to represent photographic lights and shades, and these protuberances will absorb, take up or carry the dye or ink in a few seconds, and yield a fine grain point which can be enlarged without showing prominence. The process is used for producing copies of kinematograph films in monochrome or colours. Various alternative methods are described for carrying out the process, and formulµ for these alternative methods are given. An accelerating agent such as sodium carbonate may be included in the developer. The hardening may be done in stages. Processes involving bleaching and re-exposure and reversal of the image are described. Exposure may be effected through the base. Very thin emulsions may be used. Coloured emulsions may be used and exposed with light of complementary colour. Specifications 1436/81, 17773/89, 27957/08, 18965/11, 20555/12, 5100/15, 127,953. 135,477, and 172,342 are referred to. Reference is also made to the use of potassium iodide in the developing composition described in Specification 187,932, and to the methods of printing an unperforated film from a perforated film described in Specification 187,933.