Wooden panel paintings (WPPs) are among the most significant historical artworks that must be preserved for future generations. Ensuring their long-term conservation requires a comprehensive characterization of their condition, making monitoring an essential process. Thus, the primary objective of this study is to provide a comprehensive overview of the current techniques employed to study support deformations in WPPs, categorizing them into localized and full-field methods. Specifically, we provide information about linear potentiometric transducers, the Deformometric Kit, and Fiber Bragg Grating sensors as techniques that provide information about specific and isolated points on the artwork’s surface. On the other hand, digital image correlation, stereo-correlation, mark-tracking, 3D modeling techniques, and the moiré method, are discussed as techniques that analyze the entire surface or a significant part of the artwork. Each method has advantages and limitations, depending on the type of monitoring needed and the desired information. Nevertheless, these techniques contribute to understanding the behavior of the artworks’ materials under environmental fluctuations or restoration interventions, aiding the development of targeted and effective conservation strategies. Furthermore, this study seeks to evaluate the effectiveness of these methods in various conservation contexts and offers practical guidelines to assist conservators and researchers in selecting the most appropriate approach to support the long-term conservation of these invaluable historical artworks.

This paper describes an innovative method developed by the authors to support basic decisions concerning the structural restoration of a large historical panel painting which had been damaged by inappropriate attachment to a wall and ongoing exposure to severe changes in environmental humidity. The Lapidazione di Santo Stefano is a large panel (2.78 × 3.92 m²) painted by Giorgio Vasari in 1571 and has been housed since then in the Church of Santo Stefano dei Cavalieri in Pisa (Italy). Its wooden support is made of large horizontal planks glued together along their edges and stiffened by vertical, dovetailed crossbeams. The panel was tightly fastened to a church wall with several rigid bolts; due to the moisture cycling produced by rainwater leakage and a subsequent “compression set”, it had developed severe tension stresses perpendicular to the grain, resulting in cracks affecting both the wood and the paint layers. To decide how to carry out the structural restoration of the panel, it was necessary to know whether slippage could occur between the panel and crossbeams during seasonal variations in environmental humidity. Without slippage, tensile stresses would be generated in the wood and could produce further cracks and damage the paint layers. An in situ monitoring method for assessing the possibility of slippage was developed and implemented. An analysis of data collected over a period of 6 months before the structural restoration confirmed that adequate slippage was possible; hence, the decision to fully repair the cracks was taken. Monitoring continued for a year after restoration and confirmed the previous findings. This paper describes the monitoring method, the equipment used, the results of its implementation and its value as a preventive conservation tool.

In ancient buildings, timber members may require specific on-site interventions, including reinforcement or repair and sometimes the insertion of reinforcing material into grooves routed in the original sound wood. The required number, positions, and dimensions of grooves and the strengthening materials may differ according to the desired increases in bending stiffness and strength. The modulus of elasticity (MOE) of each beam is of key importance: the MOE is typically a point of weakness for wood and is considered a constant characteristic of each beam. However, taking into account the wood lost for the groove, whether the needed incisions affect the stiffness is unknown. As such, in this study, 12 old beams were accurately measured, and their static and dynamic MOEs were calculated before and after groove formation to simulate the typical processes of reinforcing interventions. One groove was routed along the length of each beam and progressively deepened in three steps. The results of tests showed how the MOE is affected by the groove depth, decreasing by up to one-third (34.1%), and that beam stiffness cannot be regarded as constant. Beam stiffness depends on the features of the beam, mainly the pith, fissures, and slope of the grain, as well as its structural integrity. Beam stiffness is strongly influenced by the cuts upon it. This study proves how the weakening effect of grooves created on-site can be assessed using the dynamic MOE and roughly predicted with a visual survey. The grooves required for strengthening beams must be thoroughly evaluated, considering the potential reduction in the mechanical properties of the beam, which goes well beyond the wood lost during cutting.

This research focuses on the analysis of the viscoelastic (VE) behaviour of panel paintings (PPs), which are artworks made of various materials. Each PP is different from others because of their unique assembly, the changes due to the passage of time and human interventions. Thus, a thorough understanding of the hygro-mechanical behaviour of PPs is needed for their conservation. This study analyses the VE behaviour of an original PP from the 16th century, taking it both as a global structure and as a bilayer system. The PP was tested under constant climatic conditions and subjected to a constant load for at least 3 days, followed by a recovery period. The experimental results show that the PP exhibited VE behaviour and that the deformation was recoverable. The PP was loaded at two stress levels, and the results were consistent with the linear VE behaviour expected for moderately loaded wood. The bilayer approach allowed us to separate the contributions of wood and the paint layer, assuming that the latter behaved elastically.