Integrated analytical methodologies for the study of corrosion processes in archaeological bronzes

The investigations on structure and micro-chemical composition of archaeological metal alloys are needed inarchaeometry. The aim of this study is devoted both to acquire information about their provenance andproduction technology, and to improve our understanding about the corrosion processes. In this paper wepresent the study of the corrosion phenomena of bronze samples, laboratory-made according to binary,ternary and quaternary alloys typical of Roman archaeometallurgical production through an integratedmethodology based on the use of non or micro invasive physical techniques. Among the analysed samples,two were artificially aged through burial in the archaeological site of Tharros, along the west coast of Sardinia(Italy). The corrosion products, typical of the bronzes in archaeological sites near the sea, have beencharacterized by non invasive and micro-destructive measurements. In particular, the corrosion patinas wereexamined through optical microscopy, scanning electron microscopy and microanalysis, X-ray fluorescenceand laser ablation spectroscopy. The use of integrated technologies allowed us to determine both theelemental composition and surface morphology of the patina, highlighting the correlation between patinanature and chemical composition of the burial context. Moreover, data obtained by the laser-inducedbreakdown spectroscopy along the depth profile on the samples, have yielded information about thestratigraphic layers of corrosion products and their growth. Finally, the depth profiles allowed us to verifyboth the chemical elements constituting the patina, the metal ions constituting the alloy and the occurrence ofmigration phenomena from bulk to the surface.