Abstract: A process for the continuous production, by extrusion, of a partly finished clay product comprising a pair of parallel strips joined in back-to-back relation by a plurality of longitudinally extending walls in the form of frangible bridges which, when the partly finished clay product has been cut into blanks and fired to harden it, can be broken to separate the blanks into two ceramic tiles. The process comprises the steps of feeding a base material to a first screw extruder having two screw conveyors in series separated by a degassing chamber, and feeding a second, differently colored, material to the degassing chamber, preferably through a second screw extruder. Downstream of the degassing chamber the screw conveyor imparts a rotary mixing motion to the two-colored clays to swirl these and then the mixture is pressed through a die plate of suitable shape, which also cuts the extruded strip to expose a face having a wood grain effect.