The best panels for the painter's use are made of oak or of straight grained mahogany. Poplar panels, when used at all, should be painted on the back and edges. Poplar is, however, a treacherous material. It is apt to warp or split. It will shrink; and if, as is sometimes the case, there is a knot in the wood, this knot will probably contain turpentine, which will penetrate any covering of paint, even though it should be an inch thick. The evil effect of a very small knot in the panel can be overcome, it is said, by rubbing the place with garlic, before painting, but I should not like to trust to this expedient.,