Cradles
Wooden cradles are used in painting to support a flat panel that is painted on, either directly or with canvas stretched over it. The cradle is constructed of wooden planks attached with mitered joints, very much like a stretcher, and either glued or screwed into the back of the panel. The cradle keeps the panel from bowing, which will happen to any panel over time, whether it's expensive birch plywood, Masonite, MDF or other composite.