The canvas being stretched on a frame, give it a layer of size, or paste-water, and then go over it with a pumice-stone, to smooth off the knots. By means of the size, the little threads and hairs are all laid close on the cloth, and the little holes filled up, so that no colour can pass through. when the cloth is dry, lay on okre in oil, which may be mixed with white-lead to make it dry the sooner. When dry, go over it again with the pumice stone, to make it smooth. after this a second couch is sometimes applied, composed of white lead and a little charcoal-black, to render the ground of an ash colour.