Let your grounds, whether oil or tempera, get thoroughly dry, and then take off the whiteness or rawness of the ground by painting over them a very thin wash of yellow ochre, mixed with a little ivory black, using yellow ochre alone in the more luminous parts, such as the sky. For a canvas prepared by Method No. 1, with oil, you must use your ordinary tube colours, mixed very thin with benzoline, or turpentine. For a canvas prepared by method No. 2, with tempera, you can use either the tube oil colours reduced with benzoline, or a thin wash of the ordinary prepared water-colour paints. Do not use water-colour over oil paint. I believe some artists do so, but it is never quite safe. ,,