Ciba-geigy Ag

Andrew W Yates

William E Long

Geoffrey E Ficken

Brian D Harradine

Michael E Dale

Michael A Wraith

David Rowland

Tetra-aza indene compounds of the formula ##STR1## wherein R.sub.1 is alkyl or a ring system and R.sub.2 and R.sub.3 are hydrogen or alkyl. These compounds are of use as image toners in photographic materials.

Tetra-aza indene compounds

Process for the preparation of silver halide emulsions containing populations of monodispersed silver halide crystals, which comprises transferring an amount of monodispersed silver halide crystals from a reaction vessel to a holding vessel, effecting growth of the silver halide crystals remaining in the reaction vessel, transferring the monodispersed silver halide crystals thus obtained to a further holding vessel followed by another growth step of the silver halide crystals left in the reaction vessel, combining all the populations of monodispersed silver halide crystals of different crystal size, and carrying out the steps required to produce a fully sensitized and concentrated silver halide emulsion. These emulsions when used in photographic materials exhibit a reduced contrast and a relatively high sensitivity.

Process for the preparation of a silver halide emulsion

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Knutsford, United Kingdom

Andrew W Yates