Preparation of stable suspension of calcined clay

Claim 1

A method for producing a stable concentrated suspension of a calcined kaolin clay pigment containing at least 35 percent by weight of particles larger than 2 microns which comprises slurrying said clay in water containing a condensed phosphate salt dispersant in amount within the range of 0.01 percent to 0.1 percent based on the weight of clay in a 70 percent solids suspension, sufficient clay being present in the slurrY to produce a fluid suspension containing about 55 percent to 62 percent clay solids, ball milling the resulting slurry with ceramic milling media having a specific gravity above 3 until the viscosity of the suspension is reduced, adding increments of calcined clay, each increment being followed by further ball milling, until the resulting slurry has a clay solids content of about 70 percent and ball milling the slurry after all of the clay has been added until a suspension having desired viscosity is obtained.