An Innovative Method for Dimensioning the Crossbeams of an Original Painted Panel, Based on Mechanical Testing, and on Numerically Modelling Its Distortion Tendency

Most panel paintings feature mechanical systems, typically made of crossbeams, designed to control the distortion of the panel. When the crossbeams are too stiff or too yielding in relation to the distortion tendency of the panel, significant damage to the artwork may occur. The evaluation of the factors causing the damage necessarily relies on the restorer’s experience and wisdom; however, in the framework of a long-standing cooperation between Opificio delle Pietre Dure (Florence) and the Research Group on Wood Technology of DAGRI Department (University of Florence), an innovative method has been developed to provide additional objective criteria for dimensioning the crossbeams system. A specific protocol was developed, based on an engineering approach and consisting of the following five “modules”: a) a Restoration Plan, developed by restorers and conservators, b) appropriate mechanical tests to evaluate the stiffness of the painted panel alone and of the crossbeams alone, c) hygroscopic tests to evaluate the hygro-mechanical behaviour of the painted panel alone, d) appropriate numerical modelling for dimensioning the panel-crossbeams system, and e) numerical and/or experimental verification of the dimensioning. This paper describes such protocol and its first implementation on an original panel painting, the Adorazione del Bambino e Committente (in brief called Nativity) attributed to Cesare da Sesto (1514–1515).