Improvements in or relating to the preparation photographic silver halide emulsions

906,908. Photographic emulsions. GEVAERT PHOTO-PRODUCTEN N.V. May 28, 1959 [May 30, 1958], No. 18194/59. Class 98 (2). Photographic emulsions are prepared by precipitating silver halide by mixing a watersoluble silver salt with a water-soluble halide in the presence of a mono-ester of polyvinyl alcohol and a polybasic organic acid, ripening the dispersion and freeing it from water-soluble salts and then redispersing it in an aqueous hydrophilitic colloid. The organic acid used to esterify the polyvinyl alcohol may be succinic, glutaric, tartaric, malic, maleic, fumaric, glutaconic, itaconic, phthalic or citric. The silver halide suspension formed initially may be precipitated by pouring it into an organic liquid as described in Specification 819,039. The silver halide grains may be washed in the usual way or the soluble salts may be removed by dialysis. The grains are then mixed with the hydrophilic colloid or binder. Suitable binders are gelatin, polyvinyl alcohol and mono-esters of the latter with polybasic acids such as are used for the initial precipitation. Binders of polyvinyl alcohol or its esters may be hardened by treating with dimethylol urea, or with aliphatic diamines as in Specification 860,632. Specification 789,823 also is referred to.