Experimental tests for mechanical properties of wooden ‘buttons’ used for attaching auxiliary supports behind panel paintings

When wooden supports of panel paintings have been severely altered or damaged and the original crossbeams are missing, new crossbeams or other types of auxiliary supports can be connected to the panel’s back-face in order to achieve desired effects including panel strengthening and control of deformations. In order to make such connection, the Restorers of Opificio delle Pietre Dure use small wooden blocks, each glued on the back face of the panel, and holding freely the head of a screw connected (often by means of springs) to the auxiliary support; the English term ‘buttons’ has been proposed for such blocks. This research examines in depth how the shape (conical or cylindrical) and dimensions (diameter in the 20-30 mm range, and thickness in the 3-6 mm range) of the buttons, all made from oak wood, influence their stiffness and load-carrying capacity.