ARCHAEOMETRIC CHARACTERISATION OF METAL OBJECTS EXCAVATED ON SUMMANO HILL

摘要

This work was aimed to characterize some metal objects found during the archaeological surveys in a late roman settlement on Summano Hill, close to Vicenza, and whose authenticity was considered uncertain by the Archaeological Soprintendenza of Veneto. The first excavation in this area is dated to the last years of 19th century, but there are no details on the unearthed findings which are now in the local museum. The region around Summano Hill had an important role in the commercial trades in North-East Italy and the top of the hill was probably a sanctuary. In addition to artefacts of great value, some objects, which look like bronze made, were found, and these manufacts have been recognized as possible fakes on stylistic grounds, but a definitive classification needs analytical and metallurgical investigation. The research is focussed on the analysis of one fibula and 4 statuettes, of which one represents a narrow female figure with some analogies to the Etruscan "Ombra della sera", while the others show a votive purpose. The preliminary EDXRF investigation performed in the laboratory of Padua University has revealed that not all objects are fake forged with brass and unrelated to the archaeological context; in fact a small statue so-called Ercole Orante is made of bronze with lead and, therefore, could be compatible with the ancient techniques of production. The possibility of studying a cross-section of the statuette called Copy of Ombra della Sera and of the fibula by scanning electron microscopy (SEM), coupled with EDS spectrometer, has allowed to obtain information concerning the microstructure of this type of findings: it is an α-brass with Zn content of about 35 % and characterized by the addition of Pb (～2 %). The investigations have also detected the presence of particular inclusions belonging to the family of iron alloys Fe-Si, evidence of a possible use during the process of reduction of Pb- or Zn-minerals, not removed in the subsequent stages. In conclusion, the high percentage of Zn (～31 %), the presence of inclusions of Pb, Al and Fe and imperfect fusion let hypothesize that the production has taken place in recent times, but, in any case, after the industrial revolution (1830). Moreover, the study of surface patina has highlighted the absence of typical elements of artificial patinas as Br, I, Se, S, and also the thickness of the alteration layer, not so deep, has reinforced the belief that it is not a modern fake.