Climate induced deformation of Panel Paintings: experimental observations on interaction between paint layers and thin wooden supports

Abstract

This work describes the experimental evidence of the deformation induced on a XVI century panel painting by climate uncontrolled fluctuations and on structural replicas under controlled laboratory conditions. The objects under measurement have a very thin wooden support (6 mm), caused by thinning and cradling of the original artefact during a restoration made at the beginning of the XX century. This kind of artefacts are very susceptible to suffer mechanical damage. The data of experiments carried out on the panel and in laboratory conditions show a characteristic behavior, similar to bimetallic strip warp and an interaction between hygroscopic asymmetry and mechanical asymmetry, inducing a peculiar stress dynamic in the interface wood-paint layer during climate fluctuations. In collaboration with the conservators involved in the restoration process, the effect of buffer hygroscopic systems on the warping has been studied.

Hygromechanical behaviour of wooden panel paintings: classification of their deformation tendencies based on numerical modelling and experimental results

“…In the performed tests, all of the variables remained the same except for the induced hygroscopic asymmetry (only the back was allowed to exchange humidity), and it can be deduced that the internal moisture gradient has a critical influence on panel behaviour. As stated in [24], the rigidity of the ground layers can cause a lack of FW behaviour. However, the presented numerical modelling and experimental results clearly demonstrate the necessity to couple the rigidity and the emissivity of the paint layers.…”

“…In fact, wood and paint layers show different hygromechanical properties [14,15], with ground layers stiffer than wood in its transverse directions, and the paint layers due to their complexity and despite their small thickness can significantly affect the deformational behaviour of the whole panel. Their mechanical contribution to the permanent deformation must be taken into account [1,21,24]; b) Transient deformation In addition to permanent deformations, transient deformation can also occur as a consequence of RH variations. These variations arise from the hygroscopic asymmetry between the two faces of the panel painting, the bare wood on the back and the painted face on the front.…”

Coupling numerical and experimental methods to characterise the mechanical behaviour of the Mona Lisa: a method to enhance the conservation of panel paintings

“…The conservation of panel paintings is a topic that researchers from various fields have dealt with for the last 70 years, at least, from different points of view. Some have investigated the hygro-mechanical behaviour of the main materials making up such artwork, tested on new materials [1][2][3][4][5], others the hygro-mechanical behaviour of mock-ups tested in the laboratory [6][7][8][9][10] and some others numerical modelling based on mock-up behaviour or literature data to interpret their behaviour [11,[12][13][14]. The present research rather focuses on an authentic artwork, as already proposed by [15][16][17][18][19][20], following the consideration that each panel painting shows a specific hygro-mechanical behaviour which should be known for its preventive and remedial conservation, as highlighted both by testing and numerical modelling in [21,22].…”