Manufacture of tabular habit silver halide crystals for photographic emulsions

Abstract

A process for the manufacture of photographic silver halide emulsions wherein the silver halide crystals are of tabular habit bounded by (100) cubic faces and which have an aspect ratio of from 1.5:1 to 7:1 is provided. The size of the crystals is from 0.2.mu. to 3.0.mu. in edge length, and they are obtained by adding an aqueous solution of a water-soluble halide and an aqueous solution of silver nitrate to an aqueous colloid medium by a double jetting technique at a controlled pAg value of between 4.0 and 8.0 and at a controlled constant temperature within the range of 35.degree. to 75.degree. C to produce monodispersed untwinned seed crystals. The seed crystals are then increased in size by Ostwald ripening in the presence of sufficient ammonia and alkali halide to favor the cubic habit of the crystals at a temperature of between 30.degree. to 70.degree. C. The photographic silver halide emulsion exhibit a high contrast on exposure and development.

Dependencies are inferred from the claim text.