A mineralogical approach to the authentication of an archaeological artefact: Real ancient bronze from Roman Age or fake?

Abstract A bronze statue, coming from a judicial seizure and representing a satyr (Silenus), was examined to determine its provenience and the historical period of production. The iconological aspects, colours, patina and conservation state are strictly compatible with ancient bronze production in Imperial Roman age but a doubt on the authenticity was cast by the presence of nineteenth and twentieth century copies of original Herculaneum statues produced by Chiurazzi smelter. Analyses by optical microscope, XRD and SEM–EDS have been performed to characterize the samples collected from the surface of the statuette, a little piece of alloy and the casting core. The right arm of the statuette was broken and in the internal part, some charred tissues were present, allowing to perform a 14 C-AMS dating. Three possible dating has been assigned, but not before the 1640 ± 30 AD. Strong corrosion features like a well-formed and stratified patina were present, suggesting a long lasting alteration and indicating that patina's investigation cannot be the only criteria for authentication in this case. Gypsum in the casting core and a ternary alloy in the bronze, like the one used in the Chiurazzi forgery have been found. The origin from Vesuvius area is confirmed by the finding of minerals present in subsilicic alkalinic volcanic environment.