The Use of Moisture Barriers on Panel Paintings

maintain an equilibrium between its moisture content and that of the surrounding atmosphere. Several distinctly different methods may be used to reduce the movement of wood and to minimize warping, checking, and splitting. Some, but not all, of these are appropriate for the wood which supports a painting. I. Boards cut along the radii of a log move and warp less than those cut at a tangent to the growth rings. This has long been recognized, so that quartered, that is radially cut, planks were preferred and used for painted panels. Such selection has undoubtedly simplified some serious problems of conservation. 2. Mechanical systems of cleats, clamps, and other devices to restrict the movement and warping of wood are a common feature of wood construction. Cradles of varying design have been used to check the warping of panel paintings. All such devices put wood under either compressive or tensile stresses. Some of these stresses may be absorbed by the internal cellular structure, and some by the inherent plasticity of wood substance [2]. Beyond the limits of these accommodations lies the danger of rupture. However, paint on a panel is rigid and, having no margin of tolerance to stress, is usually broken before the supporting wood is ruptured. 3. Control of the atmospheric environment of wood acts indirectly to control the movement of wood. In a museum, air-conditioning providing humidity control is, of course, the ideal method for controlling wood movement. Adequate control may also be obtained in exhibition cases by relatively uncomplicated systems. In shipping cases used for short periods of time, control may be achieved by insulation, moisture seals, and the proper use of the stabilizing effect of packing materials and dunnage. 4. Recently various kinds of chemical treatment have been used to stabilize wood