Non-Invasive Characterization of Maiolica Layer Structure by Terahertz Time-Domain Imaging

The characterization of the layered structure is of paramount importance for the study of maiolica wares (tin-glazed pottery). This paper presents the potentialities of Terahertz Time-Domain Imaging (THz-TDI) as a tool to perform non-invasive stratigraphic analysis of the maiolica objects under test. Samples with different types of stratigraphy, as testified by preliminary SEM-EDS analysis, were investigated by THz-TDI in laboratory conditions. The collected THz data were processed by means of noise filtering procedures and a time-of-flight-based imaging approach and the achieved results corroborate the ability to identify glaze layers, whose electromagnetic properties, i.e., the refraction index and the dielectric permittivity value, were estimated by taking into account both THz-TDI and SEM-EDS data. However, layers applied over the white glaze (namely, a transparent overglaze and a luster decoration) were not detected, probably since their thickness is below the range resolution of the adopted THz-TDI system. Morphological features hidden under the surface were also identified and they provided information about the manufacturing technique.