Ilford Limited

Trevor J Maternaghan

Clive W Mowforth

James F Bullock

Rolf Steiger

Geoffrey E Ficken

Victor W Dolden

Karen N Harvey

Douglas J Edwards

There is described a method of preparing a silver halide emulsion wherein the silver halide crystals are of the twinned type which comprises the steps of (a) forming or providing in a colloid dispersing medium silver halide crystals containing at least 90 mole % iodide, at least 90% of which are of the hexagonal lattice structure with a mean thickness of less than 0.6 microns and a mean aspect ratio of greater than 2:1 (b) mixing in the dispersing medium containing the said silver halide crystals an aqueous solution of a silver salt and an aqueous solution of an alkali metal of ammonium bromide or chloride (or mixtures thereof) so forming twinned silver halide crystals containing iodide and the halide being added, optionally (c) adding a silver halide solvent to this dispersing medium and so causing the growth of the twinned crystals by Ostwald ripening and optionally (d) then causing the twinned crystals to increase in size by adding to the colloidal dispersion further silver salt solution and a further alkali metal or ammonium halide and then finally optionally (e) removing the water-soluble salts formed and chemically and spectrally sensitizing the emulsion.

Twinned emulsions made from silver iodide seed crystals having an aspect

There is described a method of preparing a silver halide emulsion wherein the silver halide crystals are of the twinned type which comprises the steps of (a) providing in a colloid dispersion medium silver halide crystals containing at least 90% iodide and at least 80% of which are hexagonal lattice structure with each displaying predominantly a single basal face, (b) mixing in the dispersing medium containing the sail silver iodide crystals an aqueous solution of an alkali metal of ammonium bromide or chloride (or mixture thereof) so forming twinned silver halide crystals containing iodide and/or the halide or halides being added, optionally (c) adding a silver halide solvent to the dispersing medium and so causing the growth of the twinned silver halide crystals, and optionally (d) then causing the twinned crystals to increase in size by adding to the colloid dispersing medium further aqueous silver salt solution and further alkali metal or ammonium halide and then finally optionally (e) removing the water-soluble salts formed and chemically sensitizing the silver halide crystals.

Silver halide emulsions containing twinned silver halide crystals

Compounds of the formula ##STR1## where A represents the atoms necessary to complete a benzoxazole or naphthoxazole ring which is optionally substituted, R.sub.1 and R.sub.2 are each alkyl, hydroxyalkyl or alkoxy alkyl groups wherein the alkyl moiety comprises 1 to 4 carbon atoms, R.sub.3, R.sub.4, R.sub.5 and R.sub.6 are each hydrogen atoms or alkyl groups having 1 to 4 carbon atoms or phenyl groups, and X is an anion.

Monomethine compounds

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Knutsford, United Kingdom

Trevor J Maternaghan