Defect detection of wall paintings in the Château de Versailles using TV-holography and IR thermography

Monuments are continuously submitted to external events like water infiltration or condensation, temperature variation, soil instability, that lead to internal damage of the structure itself as well as of its surfaces. Wall paintings are then submitted to stresses that may cause cracks, internal de-lamination of the plaster or de-bonding between canvas and plaster. In the frame of the restoration of the "galerie des glaces" in the "château de Versailles", TV-Holography and IR Thermography have been used to investigate the wall paintings of the vault. The surfaces to control were either direct paintings on the plaster or paintings on canvas backed on the plaster. IR Thermography for art work and in particular for wall paintings has only recently been used. The technique allows to record transient temperature maps, when slightly heating the surface during a short time. Then, nonhomogeneities in the conductive heat transfer are related to de-bonding or de-lamination. The time parameter gives information on the depth of the defect. A calibration procedure has to be carried out to ensure reliable defect detection. Speckle interferometry is a Non Destructive Testing technique that is currently used in industry. For the wall paintings, we have used TV-Holography associated with a continuous wave laser. The technique allows, 13 metres away from the surface, to detect parts of the paintings that were vibrating due to an acoustic excitation. The control processes based on these two technologies is detailed as well as the results obtained and a comparison with manual investigation is done.