GB1183176A - Process for the Development of Photographic Silver Images - Google Patents

Abstract

1,183,176. Photographic development. CIBA Ltd. April 19, 1968 [April 20, 1967], No.18659/68. Heading G2C. Silver salts are photographically developed in an acid medium by the reduction product of a 1, 4-diazine which has at most been reduced to the dihydro stage. Preferred diazines from which developers are prepared are pyrazines, quinoxalines and phenazines of formula: in which either (1)R 1-4 are each H, carboxyl or C 1-3 alkyl or (2) R 1 and R 2 complete an optionally substituted benzo ring, and R 3 and R 4 are each H, alkyl, phenyl, heterocyclyl, acetyl or benzyl or together complete a benzo ring which is either unsubstituted or contains an NH 2 group in one α-position and an OH or NH 2 group in the other α-position. Other diazines are also listed. The diazine may be chemically or electrolytically reduced in situ (e.g. by Cr SO 4 , sodium dithionite or hydrogenation), or a stable reduced diazine used. The reduced diazine may be used in a developer solution (e.g. one containing 0À1 molar H 2 SO 4 , acetone, dimethylformamide or ethanol as solvent, optionally a buffer to maintain a pH of 0-4 and KBr, KCNS or phenylmercaptotetrazole), a monobath, or a silver halide material (e.g. in the form of a dispersion, a solution in a crystalloid or in microcapsules). The developers are particularly useful in silver-dye-bleach processes (since the unreacted developer can bleach azo and other reducible dyes), black-and-white processes and silver-salt diffusion processes, but may also be used in other processes.