A method for preparing a heat stable aqueous slurry of a bulking pigment suitable for use in coating or filling paper which comprises preparing a fluid aqueous suspension of particles of kaolin clay, adding thereto a water-soluble cationic polyelectrolyte, the amount of said cationic polyelectrolyte being sufficient to substantially thicken and flocculate said fluid suspension, acidifying the resulting flocculate clay suspension, bleaching the clay in said suspension with a hydrosulfite salt, filtering said acidified suspension to recover bulked clay, washing the filtered clay and adding minimal amounts of a sodium polyacrylate and a nonionic surfactant to the recovered bulked clay to provide a fluid suspension of bulked clay.