-There are many points in favour of painting on wood. Correggio, Rubens, and many of the great masters of the Italian, Flemish, and Dutch Schools used this material as a painting ground after previously preparing the surface with white. Pearwood, boxwood, and oak were generally employed for making panels, and for very large ones, the boards were cemented together with a glue made from cheese, that formed the panel into a wide board, as firm as if made out of a solid plank. Mahogany is now almost invariably used for panels, but they are not very extensively employed on account of their greater cost compared with other grounds. Unless carefully prepared they are liable to warp or split, but if properly made they are preferable to any other form of ground for moderate sizes. In order to preserve them flat the wood must in the first instance be very carefully selected, and they should be painted with an equal quantity of colour on 'both' sides.,The early oil painters prepared their panels with two or three coats of size, then a layer of coarse gesso (a kind of plaster of Paris) and on this at least eight layers of a finer description of the same material. In the Italian school of a later period the grounds were generally of pipe-clay mixed with chalk.,