Active Thermography for Non-invasive Inspection of an Artwork on Poplar Panel: Novel Approach Using Principal Component Thermography and Absolute Thermal Contrast

The conservation of the works of art represent a topic of global interest. The development of effective tools based on advanced technology for analysing and monitoring their health-state is essential to assuring their preservation. In fact, detecting and preventing the formation of defective areas or assessing for an accurate pre-restoration analysis are the main objectives of non- destructive inspection. Active thermography is a well-known non-invasive imaging technique and reliable tool for providing a fast and low-cost analysis of a work of art. In this study we combine the potential of Principal Component Thermography and of Absolute Thermal Contrast to analyse thermal images acquired in-situ on a poplar panel painting representing an original artwork dating in the end of XVI century. We first optimized the thermal stimulation parameters in the laboratory using special phantom samples. These samples were specially made by reproducing in high fidelity the structural properties and materials of the artwork in order to perform effectively the preliminary tests. Then we moved the equipment in-situ by performing the non-destructive inspection directly on the real artwork. We have developed a specific experimental protocol that combines active thermography with two specific and appropriate image processing modalities that allowed us the effec- tive detection of various types of defects in the painting layer. We report a complete analysis and deep discussion concerning the detection and characterization of the defects. Results show that our diagnostic protocol is a powerful tool in assessing the pre-restoration health-state and suitable for in situ analysis of wood artworks.