The role of IRT in the archaeometric study of ancient glass through XRF and FORS

The process of degradation of archaeological glass subjected to centuries of burial can be of great relevance: typical consequence of degradation in the original vitreous material is rainbow-like iridescence due to chemical alteration of surface layers, salts formation and ion migration. The research presented in this paper is focused on the study of a collection of Roman glass (I - II century A.D.) held by the Museo Civico Etnografico Archeologico Fanchini of Oleggio, Italy. Chemical characterization (namely flux, chromophores and opacifiers determination) has been performed by a combination of X-Ray Fluorescence (XRF) and Fibre Optics Reflectance Spectroscopy (FORS) in the UV–Vis-NIR region. Conservation conditions have been studied and degraded areas have been mapped through Infrared thermography (IRT). IRT is a non-invasive method typically used to measure the apparent temperature of objects and represent it as pseudo-colour images. In the present work, we demonstrate the feasibility of IRT for identifying and mapping glass substrate defects due to ageing of glass, assuming that they may be considered as thermal anomalies. Thermogram sequences have been processed by high order statistical analysis, which is particularly suitable since it is based on automated processes where the output is a single representative image. The use of a thermal camera allows furthermore to perform remote analysis in areas hardly reachable in a fast and effective way.