Evaluation of the porosity of natural and artificial stones by Infrared Thermography

With the designation of Filippo Juvarra as the first architect of the Savoy kingdom, Turin saw the flourishing of new monuments in which he used an interesting variety of natural stones. Prominent among these is Chianocco marble, recognisable on the Turin façades of Palazzo Madama and Rivoli Castle. This material, which is easy to work on, nevertheless needed to be well selected to reduce its strong inhomogeneity and contain its high porosity, leading to even intense degradation over time. The need expressed by restorers to find relatively quick in situ methods to check the behavior of the stone material for conservation purposes, e.g., by assessing the possible presence of surface protectants, provided the opportunity to start an experiment that made use of infrared thermography. The use of TIR makes it possible to non-destructively analyse surface heat exchange during and after the contact sponge method. In the present work, the contact sponge method was integrated with thermographic monitoring to observe the evolution of the process of spatial diffusion and moisture evaporation over time, in a dynamic manner. The path adopted started with the analysis of the stone directly onsite. It continued in the laboratory with tests on altered samples of the same material taken in situ and unaltered samples taken in the quarry according to the principles of the inductive method. The project now goes on by testing materials with similar characteristics, but with greater uniformity. The data obtained show the effectiveness of the thermographic technique for analysing the porosity of the stone; in the cases under examination, it was possible to characterize the material's response to absorption and diffusion of water.