GB265630A - Improvements in photographic developing processes more especially for use with printing surfaces - Google Patents

Abstract

265,630. Soc. de Photochimie Elka. Feb. 8, 1926, [Convention date]. Etching.-The development of silver bromide layers to produce differential hardening, more especially for the production of photo-mechanical printing-surfaces, is effected by partly developing with a tanning developer and completing the development with a non-tanning developer. The tanning of the exposed parts is thereby accelerated without any hardening of the unexposcd parts. After transfer to a metal plate and hot water treatment the bare metal, if necessary, can be completely cleaned by rubbing with a pad impregnated with a slightly abrasive mixture. After inking the hardened gelatine can be removed by acid and the plate used for litho transfers, or engraved for use as a typographic plate. Alternatively, and for line or half-tone photogravure, the plate can be etched, as with perchloride or iron. In another process the bare metal after washing out the soft gelatine, can be metallized as with silver. The silver coating can be produced from the silver in the picture layer, processes of this being described. The Specification as open to inspection under Sect. 91 (3) (a) comprises also the following subject-matter :-When metallizing the bare metal of a plate after washing out the soft gelatine, leaving a hardened gelatine picture thereon, the coating metal is preferably one widely separated in the scale of electrolytic tensions. The effect of a silver reserve on a zinc plate in subsequent etching is also described. Also in the preparation of relief plates, the plate having the gelatine relief thereon, which is fully hardened, as by formol, is coated with silver in the bare parts, inked up, the gelatine removed, the ink coated with resin and warmed, and the plate etched. The etching can be deep owing to the silver reserve. Further re-etching can be effected by cleaning the plate, covering the surface of the lines with a removable coating, removing the removable coating with the ink from the metallized parts, and re-metallizing these parts preliminarily to a further etching process. This subjectmatter does not appear in the Specification as accepted.