GB431384A - Improvements in or relating to the production of negatives with photographic images thereon of enhanced quality - Google Patents

Abstract

431,384. Photographic processes ; photo - mechanical printing surfaces. FIELD, A. E., 113, Ashmore Road, Harrow Road, London. Dec. 7, 1933, No. 34497. [Class 98 (ii)] A negative more especially for use in the production of photomechanical printing-surfaces is subjected to the action of a bleaching re-agent to produce a photographic image of positive appearance, retouched, etched, or reduced by means of a silver halide solvent, and finally subjected to the action of a solution which blackens the silver salt image and re-converts the image to a negative image. The bleaching bath may comprise (1) iodine in an aqueous solution of potassium iodide, (2) potassium ferricyanide and potassium bromide, or (3) potassium permanganate acidified with acetic or hydrochloric acid. The retouching or etching may be effected with a potassium cyanide bath, the portions of the image not to be retouched being coated with cellulose varnish or litho crayon. Other silver halide solvents such as sodium thiosulphate, or potassium iodide may be employed. After bleaching with iodine solution, the excess is removed with a potassium hydroxide bath. After bleaching with potassium permanganate, stains are removed by treatment with a bath of potassium meta-bisulphite. After retouching with potassium cyanide, the scum is removed by treatment with dilute nitric or acetic acid. The re-blackening bath may comprise sodium sulphide, or a metolhydroquinone developer, or a mixture of sodium sulphide and a developer. After washing, the negative may be intensified with mercuric chloride, bromide or iodide, or a redeveloping and intensifying solution comprising adurol, citric acid, silver nitrate, nitric acid and water may be employed. The fixing solution for the original negative may include potassium iodide.