Canvass, panel, and millboard - are used indiscriminately for pictures, but canvass is the cheapest in proportion to its size, is generally made use of for pictures of considerable dimensions, and is usually sold ready prepared and stretched on straining frames; which are frames fitted with wedges to their inner corners, by driving which, the canvass may be tightened, should it chance to become inconveniently loose, as it sometimes does.