GB100098A - Improvements in or relating to Methods of Bleaching and Dyeing Photographic Images. - Google Patents

Abstract

100,098. Brewster Film Corporation, (Assignees of Miller, H.). Feb. 26, 1915. [Convention date]. Colour photography; toning and after-treatment.-Coloured photographs are obtained by converting a silver image into a substantially invisible, colourless, transparent, dye-absorptive substance, which is thought to be a hydrosol or hydrogel of a silver salt and requires no fixing, and dyeing it; such images may be used for all forms of coloured photographic work or kinematography. The image is bleached by treating it with a solution of iodine in an iodide, preferably potassium iodide, or with a solution containing potassium iodide and potassium bichromate, permanganate or persulphate, or cerium permangar.ate or persulphate, or a similar substance which releases iodine from the potassium iodide. The solution may also contain acetic, hydriodic, nitric or formic acid. Suitable formulµ are (1) potassium iodide 5 grams, iodine, 0.15 grams, 3 per cent acetic acid 5 c.c., water to make 100 c.c., (2) potassium iodide 5 grams, potassium bichromate (1 per cent solution) 5 c.c. to 25 c.c., 3 per cent acetic acid 5 c.c. to 25 c.c., water to make 100 c.c. Considerable variation of the first of these formulµ may be made if the free iodine is present in the ratio of 1 per cent to 4 per cent of the potassium iodide, but higher concentration of the potassium iodide than 10 per cent is not advisable. The excess of iodine is removed from the treated image by a reducing agent such as sodium bisulphite, and the image, after washing, is dyed, preferably with a basic aniline dye in a slightly acid bath, and finally washed to remove excess dye. The dyeing-solution may be capable of giving an opaque or transparent image, and the film may be hardened with formalin &c. to ensure clear high-lights after dyeing. The silver image may be redeveloped if desired. Specifications 10258/07, 27818/09 and 25084/12 are referred to. The Specification as open to inspection under Sect. 91 (3) (a) states also that the bleaching bath may comprise a solution of iodine or other halogen in an iodide or other haloid, or may be such as to convert the silver into a chromate, ferrocyanide or ferricyanide, and that the silver of the image may be removed after dyeing by .potassium cyanide or hypo. the dye being first fixed. This subject-matter does not appear in the Specification as accepted.