Process for the preparation of high chloride (100) tabular grain emulsions

A process of precipitating a photographic emulsion containing silver halide grains comprised of iodide and at least 50 mole percent chloride, with tabular grains having {100} major faces accounting for greater than 50 percent of total grain projected area, comprised of the steps of

• (1) separately introducing soluble silver and halide salts into an aqueous dispersing medium containing a gelatino-peptizer so that grain nuclei are formed while the dispersing medium is maintained at a pCl in the range of from 0.5 to 3.5, the halide being at least 50 mole percent chloride, based on silver, with any remaining halide being bromide, and
• (2) following step (1) completing grain growth under conditions that form the {100} major faces of the tabular grains,
• wherein, prior to step (2),
• (a) a solution containing elemental iodine is introduced into the dispersing medium, the iodine solution having a volume that is less than 10 percent the volume of the emulsion at the conclusion of step (2),
• (b) after 0.01 percent and before 3 percent of total silver has been introduced, the iodine is converted to iodide ion, and
• (c) the iodide is incorporated into the grain nuclei to create crystal lattice defects that promote the growth of {100} tabular grains during step (2).