..but upon cloth and flexible bases, such grounds [plaster] are too stiff and friable; such bases require, therefore, a ground more of their own yielding and elastic nature, and better suited to assimilate with the materials of oil painting, such as is afforded by tempering earths and metallic oxides with the most tenacious drying-oils, and laying them evenly upon the cloths, first coated or primed with size.,