Paola Mazzanti

Verifying the operation of an elastic crossbar system applied to a panel painting: the Deposition from the Cross by an anonymous artist from Abruzzo, sixteenth century

This study deals with the post-treatment evaluation of the elastic crossbar system already designed and installed on the recently restored panel painting Deposition from the Cross by an anonymous artist from Abruzzo (sixteenth century). After the restoration, the panel and the crossbars were subjected to mechanical tests to identify their elastic characteristics. Then the panel, equipped with the elastic crossbar system, was subjected for about two months to controlled environmental cycles made up of approximately constant humidity periods. During the two months, the forces exerted by the springs and the deformations of both panel and crossbars were continuously monitored. A mathematical model, calibrated on the specific parameters derived from the analysis of the panel, provided the deformation that the panel would have shown without the crossbars; comparing the model output with the measured data provided a restraining effect (RE) of approximately 7% (RE could range between zero – no restraint – and 100% – total restraint). Future developments of this project will define appropriate procedures to design an elastic crossbar system for a given panel, once the expert judgement of restorers has identified the most desirable RE to be achieved.

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

Abstract When wooden supports of panel paintings have been severely altered or damaged and the original cross beams are missing, new cross beams or other types of auxiliary supports are connected to the panels back-face in order to achieve desired effects including panel strengthening and control of deformations. Some conservation laboratories 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; such blocks being called in Italian ‘piedini’ or ‘bottoni’, the English term ‘buttons’ is proposed here. This paper reports research aiming to characterize the mechanical behavior of three types of ‘buttons’ having different geometries and made of various wood types (oak, walnut, lime, beech, and a medium density fiberboard). Short-term mechanical tests (∼1 minute duration) were performed with a universal testing machine by axially pulling out the 4 mm diameter steel screw from the button, glued onto a dummy board. Load and deformation were recorded, and the load–deformation curves were analyzed. The results show that the deformability and the load-carrying capacity of the buttons were influenced primarily by the manufacturing geometry and secondarily by the wood density.