Terahertz analysis of stratified wall plaster at buildings of cultural importance across Europe

Terahertz (THz) radiation emerges as a powerful, non-invasive tool for analyzing sub-surface layers of wall plaster in cultural heritage sites. This study demonstrates its ability to penetrate up to one centimeter into wall surfaces, revealing stratified features such as paint layers and under-paintings without damaging the structure. At Chartres Cathedral, THz analysis confirmed the presence of 13th-century sub-surface paint layers, while at Riga Dome Cathedral, it detected obscured surface paintings applied in 1941. Additionally, the technique identified sinopia under-painting on uneven stonework at the Chapel of the Frescos in France. Unlike radar or infrared/ultraviolet methods, THz radiation uniquely bridges the gap between surface and deep sub-surface analysis, offering high-resolution insights into the layered complexity of historical plasters.

Walker, G. C., Jackson, J. B., Giovannacci, D., Bowen, J. W., Delandes, B., Labaune, J., Mourou, G., Menu, M., & Detalle, V. (2013). Terahertz analysis of stratified wall plaster at buildings of cultural importance across Europe. Optics for Arts, Architecture, and Archaeology IV, 8790, 87900H. https://doi.org/10.1117/12.2020596