A method for controlling the viscosity of dispersed clay slurries is disclosed. In accordance with the invention, the problem associated with shipping or storing clay slurries in tank cars or tanks, that is, significant increases in the viscosity of the slurry which often results in the formation of a gelled mass, is overcome by the addition of gluconic acid or a salt thereof, such as sodium gluconate. The addition of the gluconic acid or the salt serves to control the viscosity of the clay slurry in a manner such that it remains at a substantially uniform and low level even when the slurry is shipped or stored over extended periods of time. The gluconic acid or gluconate is added to the slurry in relatively small quantities, i.e., up to 5.0 pounds/ton clay and unexpectedly does not affect the properties or characteristics of the clay pigment or product.