The best are absorbent, as the oil sinks in and leaves the colours pure and brilliant. Oil darkens, and its use is to be avoided. A good preparation for canvas, or for sketching boards, can be made thus: - Melt and boil, a quarter of a pound of glue in a pint of water. In a pint and a half of water mix a pound and a half of whiting. In a half pint of water melt and boil three ounces of soap. Mix the whole together, stirring it well, and boil for a few minutes. This makes an excellent absorbent preparation. If a lead surface is preferred, it can be painted with white lead and spirits of turpentine.,,