Suitable dispersing agents used for primary dispersion in practice of the present are conventional and include water soluble salts of a condensed phosphate, such as a pyrophosphate, e.g., tetrasodium pyrophosphate, (TSPP), a water soluble salt of a polysilicic acid, for example, sodium silicate, or a water soluble organic polymeric dispersing agent, for example a polyacrylate or a polymethylmethac