Conservation of artworks is of paramount importance nowadays around the world. Clever conservation by using non-destructive testing techniques is highly appreciated by restorers and art historians. Among these, active infrared thermography needs the use of numerical simulations concerning the heat transfer from the heat source into the target. This, in order to gently heat the precious surface by avoiding any type of damage, such as colour changes and/or shrinkage and warpage effects, therefore, the understanding of the nature of the pigments, as well as the mapping of the support and eventual foreign materials is of primary importance in the survey. It is possible to accomplish these tasks by applying, e.g. X-Ray Fluorescence spectroscopy and radiography (X-Ray), respectively. Here, the latter techniques have been used on an ancient marquetry sample. Consequently, a thermographic inspection was performed, while a thermal–numerical simulation was implemented in ANSYS® environment. Numerical simulations were able to visualize some types of defects by calibrating the thermal inspection based on a comparison among defective and sound areas. Results demonstrated how such an integrated method is useful to provide robust information without damage to the work of art under restoration.