Patent GB-611846-A (GB)
Title: Improvements in or relating to photographic sensitive materials
IPC: G03C1/825
Filed: 1946-05-10
Abstract: 611,846. Photographic compositions. DU PONT DE NEMOURS & CO., E. I. May 10, 1946, No. 14179. Convention date, June 7, 1945. [Class 98 (ii)] A photographic composition comprises a hydrophilic colloid which has dispersed therethrough finely-divided discrete particles of silver and an optical sensitising dye. A colour former may also be included in the composition, or the latter may comprise a hydrophilic colloid colour-former with the particles of silver and the dye. The composition is made by exposing a silver halide colloid emulsion, developing it, washing to remove developing agents, and adding the dye, and the colour former if such is to be included ; and it may be coated on a support such as film, plate or paper to give an element inert to light, but which can be rendered light-sensitive prior to use by bleaching in darkness. Example 1 specifies the addition of ammoniacal silver nitrate solution to aqueous gelatin containing ammonium bromide, with stirring, under ordinary illumination, chilling, setting, shredding and developing in a vigorous black and white developer containing 2.4-diaminophenol hydrochloride, fixing the shredded material in hypo, washing, melting, adding a dimeric sensitising dye of the type described in example 1 of Specification 573,394, and coating the resulting composition on a transparent film support. In use the element so produced is bleached in an aqueous solution of ammonium persulphate and potassium bromide, bathed in sodium bisulphite to eliminate oxidising agents, washed, dried, exposed and developed to yield a normal silver image. Example 2 indicates substitution of 1.11-diethyl-2.41-carbocyanine iodide for the sensitising dye of example 1. Examples 3, 4 and 6 indicate the use of colour formers in the element of example 1. Example 5 describes a cellulose acetate film support having two of the colloid-silver coatings, each containing a sensitising dye and a colour former, and the bleaching of the film, exposure of each layer through a separation negative with appropriately coloured light,- development in a colour-forming developer and removal of silver and silver salts to yield a two-colour image. In example 7 a three-layer film has outer silver iodobromide layers containing colour formers and an inner layer of the colloidsilver type of the invention containing a redsensitising dye ; the outer layers are printed from opposite sides through separation records with blue light, the inner layer acting as a barrier, and are developed to colour, the film is fixed to remove the undeveloped silver halide, bleached to convert all of the remaining silver to silver salts and then the inner layer is printed with red light and developed to produce a silver image which can be converted to colour by means such as dye coating. Example 8 describes a film with three of the dye-sensitised colloid-silver layers and indicates a process of bleaching the film to make it light-sensitive, exposure of it to a coloured object, and development to form dye images in each of the layers. Specifications 479,838, 489,161, 521,169, 535,341, 543,290, 547,847, 577,387, 593,088, 598,367, 598,475 and 598,476 also are referred to.