direct positive photographic silberhalogenidemulsion disguised

摘要

1,186,721. Direct-positive photographic silver halide emulsions. EASTMAN KODAK CO. May 5, 1967 [Jan.17, 1967], No.20918/67. Heading G2C. A direct-positive photographic silver halide emulsion comprises a fogged silver halide emulsion containing a pyrylium, thiapyrylium or selenapyrylium salt dye, preferably having the general formula:- where D is oxygen, sulphur or selenium, X is an acid anion and R 1 , R 2 and R 3 are each alkyl, alkenyl or aryl, any of which may be substituted, or cycloalkyl or alkoxy. The emulsion may be fogged by exposure to light or chemically using stannous chloride, formaldehyde, hydrazine, thiourea dioxide or tetra (hydroxymethyl)-phosphonium chloride, optionally in the presence of gold, rhodium, platinum, palladium or iridium salts. The dyes may be incorporated by adding dye solutions to the emulsions, or by treating the coated silver halide material with the dye solution.