Feasibility study to evaluate composition and degradation of orichalcum ingots through combined XRF and VIS-SWIR reflectance mapping

Abstract

Non-invasive and multi-analytical approaches are crucial for analyzing cultural heritage artifacts, particularly for rare and fragile specimens that must be studied in situ. The disadvantage of non-invasive techniques is their lower sensitivity and the limited information that can be collected without sampling the artifact; however, they allow the collection of multiple data sets on the same specimen. Besides, non-invasive techniques can collect more sample points or even a map on the same artifact, getting information about the whole object, considering its inhomogeneities due to possible alterations, without being biased by the chosen points. In this work, we employ an integrated instrument capable of simultaneously acquiring X-ray fluorescence and reflectance mapping in the visible-short wave infrared range to analyze orichalcum powder samples, then discussing the results in comparison with the analysis carried out using both in situ non-invasive techniques and laboratory-based non-destructive methods. These reference samples, derived from ingots recovered from a 6th-century BC shipwreck discovered off the coast of Gela, serve as a controlled dataset to validate the performance of the combined mapping approach. The aim is to assess the potential of this dual-modality system, enabling a comprehensive, bulk, and surface, characterization for future in situ applications to the ingots to check and follow the surface degradation phenomena, without the need for sampling.