THz time domain spectroscopy — Non-destructive evaluation of material detachments from exposed natural stone and ceramic objects

Environmental damages such as the detachment of original surfaces caused by cavity formation under the surface of natural stone and ceramic objects are usually not externally visible. Envirromental influences as temperature and humidity fluctuations, particularly when frost or saline accumulation forms can result in the generation of cracks, gaps, and even full detachment of parts of artwork in the exterior area. By using terahertz time domain spectroscopy (THz-TDS), we illustrate this promising method to locate and measure small subsurface cavities. This method is applied to produce three-dimensional images and pulsed terahertz “time-of-flight” measurements of the cavities.