panel

panel. Term in painting for a support of wood or other rigid material, as distinct from canvas or other flexible material such as silk. Until the introduction of canvas in the 15th century, nearly all movable paintings in Europe were executed on wood, and it was probably not until the early 17th century that canvas overtook wood in popularity and could be regarded as the standard support for oil painting. When the word ‘panel’ is used without qualification in art-historical contexts, it therefore almost invariably implies wood, but many other rigid materials have been used as supports. Painters who worked on a small scale often used copper plates, like those of engravers or etchers (Elsheimer is a leading example), and in the colonial art of South America copper and tin and even lead and zinc were employed. Various stones have also been used as supports, including marble (see Stella, Jacques) and, on a larger scale, slate, notably by Sebastiano del Piombo in several works and by Rubens in his altarpiece for S. Maria in Vallicella (the Chiesa Nuova) in Rome; the picture he originally painted, on canvas (Virgin and Child Adored by St Gregory and Other Saints, 1607, Mus. B.-A., Grenoble), was said to reflect the light unpleasantly and slate was used for the replacement to produce a more matt finish (1608, in situ). In a more experimental vein, Stubbs painted numerous pictures on earthenware panels, using enamel paints, hoping that works produced in this way would retain their freshness and resist cracking better than oil paintings. Technically his results were impressive, but the smooth, glossy finish was not to everyone's taste, and the process was too demanding and expensive to attract imitators.

The choice of wood for panels depended mainly on local availability. In Italy, poplar was most commonly used, and oak was preferred in northern Europe. Many other types were used, however; analysis of the contents of art galleries has yielded a long list, including beech, cedar, chestnut, fir, larch, linden, mahogany, olive, and walnut. Today cedar, teak, and dark walnut are favourites. The panel must be well seasoned to remove resin and gum as otherwise it may warp and split. Cennini advised that small panels should be boiled to prevent splitting, presumably because this removes some of the resin, and modern experts recommend steaming for the same reason. For a large picture several pieces had to be accurately jointed together and glued with casein, a difficult operation that is described in medieval treatises. Modern painters have also used plywood, fibre-board, and other synthetic materials as supports (see also academy board).

Painting directly on wood is not satisfactory because the wood absorbs too much of the paint and does not reflect enough light, besides reacting chemically with some of the pigments. Moreover, some woods darken in course of time. Normally, therefore, after any filling up of holes that was necessary, the panel was sized and coated with several layers of gesso, or of chalk, so that it presented a smooth, even ground. The backs of panels also require protection against woodworm and against damp, which can cause warping and rot.