Evaluation of defects in panel paintings using infrared, optical and ultrasonic techniques

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Abstract
The increasing deterioration of panel paintings can be due to the physical processes that take place during exhibition or transit, or as a result of temperature and humidity fluctuations within a building, church or museum. In response to environmental alterations, a panel painting can expand or contract and a new equilibrium state is eventually reached. These adjustments, though, are usually accompanied by a change in shape in order to accommodate the new conditions. In this work, a holographic method for detecting detached regions and micro-cracks is described. Some of these defects are confirmed by the thermographic signal reconstruction (TSR) technique. In addition, pulsed phase thermography (PPT) and principal component thermography (PCT) allow two artificial defects in Mylar to be identified with greater contrast, which is crucial to understand the topic of interest: the discrimination between defect materials. Finally, traditional contact ultrasound applications are widely applied for the evaluation of the wood quality in several characterisation procedures. Inspecting the specimen from the front side, the natural and artificial defects of the specimen are confirmed. Experimental results derived by the application of the integrated methods on an Italian panel painting reproduction, called The Angel specimen, are presented. The main advantages that these techniques can offer to the conservation and restoration of artworks are emphasised