Photothermal radiometry for non-destructive testing and characterization of cultural heritage objects

Photothermal radiometry (PTR) is very attractive for non-destructive testing and characterization of complex art objects and analysis of defects caused by ageing and environmental effects. Our preliminary studies with non-museum paintings were aimed to test and to characterize various defects on the paint layers and canvas, and also to detect under-drawings, pentimenti, etc. Flash lamps (1 to 3ms duration) were used for a rapid heating of the painting surface. A dynamic time-resolved thermal response was recorded in a significantly extended infrared spectral range (1.5 to 11.5μm) by two high speed, cooled, high sensitive mid- and long-wavelength infrared cameras. 2D images of Fourier transform phase shifts and magnitudes with micrometric spatial resolutions were obtained by fast Discrete Fourier Transform from the 10^-2 to 10² second time domain. Analytical procedures were made to improve readability of artefacts undetectable by the naked eye and to ensure non-invasive testing by time resolved surface temperature measurement. The optimal PTR parameters obtained in our preliminary studies were applied to museum paintings under restoration for non-destructive testing with the mobile PTR system. The results of our studies have demonstrated that the PTR method holds significant potential for widespread application in the inspection, documentation, preservation, and conservation of cultural heritage objects.