Exploring Thermal Quasi-Reflectography (TQR) capabilities on paintings

The stratigraphic complexity and heterogeneity of paintings are important factors to consider when imaging analyses are performed in different infrared bands. This study investigates the capabilities of Thermal Quasi-Reflectography (TQR) for the examination of paintings and proposes a framework for interpreting the MWIR response of pictorial layers. Two mock-ups reproducing characterised paint stratigraphies based on historical techniques were investigated by TQR and compared with NIR-SWIR reflectography. The results demonstrate that variations in the thickness and density of the preparatory ground significantly affect reflectivity and the detectability of concealed features in MWIR imaging, while having a limited influence on SWIR reflectography. Underdrawings and pentimenti can also be detected by TQR, although with a different response than NIR imaging and lower penetration depth than SWIR reflectography. The study highlights the complementarity of NIR, SWIR, and MWIR imaging techniques and supports the integration of TQR within a multi-technique diagnostic protocol for paintings.