This article describes a technique developed at the Walters Art Gallery during the 1930's to reduce warping, twisting and shrinkage of wooden painting panels and subsequent detachment of ground (gesso) and paint layers. Traditional methods include 1) transposing ground and paint film onto canvas, 2) reducing the panel to a thin section and mounting onto another panel, and 3) cradling. 1) and 2) fail to achieve the basic principle of preserving, intact and unaltered, the original work and materials. Muslin backing eventually imprints its weave on the paint surface. Paint and gesso layers must adjust to movements of the new wooden support. Cradling (parquetage à plat) transfers stress from the added wooden strips to the panel resulting in splitting, blistering and paint loss. Areas between strips move differentially to restrained areas. If a panel painting's condition is sound, leave it alone. Frames can accommodate distortion. If the painted surface is unstable, protect the paint film, straighten panel by controlled use of humidity, and apply a wax and resin mixture by heat or immersion. For large or weakened panels, attach aluminum strips or backing for mechanical strength. Paintings treated at the Gallery were still in good condition 10 years later. This article is a reference for the historical documentation of preserving panel paintings.