Ceramiche a vernice nera della necropoli etrusca di Valle Trebba, Spina (FE): dati archeologici e archeometrici

The project of study of the necropolis of Valle Trebba in Spina, coordinated by the Chair of Etruscology and Italic Archaeology of Bologna University in agreement with the Superintendence for Archaeological Heritage of Emilia Romagna, promotes a systematic analysis of black glazed pottery in a context of great proportions and relevance. Insights on local and imported productions of black glazed pottery in the Etruscan area of the Po Valley are few in order to date. Regarding Spina, the considerations on these productions in scientific literature are limited essentially to the autopsy of findings and the study of published funerary contexts. The sampling (64 samples) and the results of archaeometrical analysis presented here involved mainly Attic, Volterra and local black glazed pottery (end of the VIth-IIIrd century BC). The primary objective of this multidisciplinary approach in the study of black glazed pottery is to identify and single out specific techniques of each production, then to relate them to the autoptic criteria generally applied to the characterization of these ceramics in archaeological studies. The secondary purpose is to investigate the possible presence of vessels locally produced as an imitation of imports from Attica, that remained so far a hypothesis in scientific literature. The samples, previously cleaned of the glazed layer, pulverized and washed in deionized H2O, have been analyzed using mineral-geochemical methods. Therefore, the powders have been examined to determine the mineralogical composition by di raction analysis (Philips PW1710 Di ractometer) and thermal ones (TG, DTG, DTA) with heating from 20° C up to 1000° C, in a stream of CO2 and a heating rate of 20° C per minute (Apparatus Thermal Setaram LABSYS), and the chemical composition through X-Ray Fluorescence (XRF Philips PW1480). The thermal analysis allows us to quantify the loss in weight % (LOI) undergone by each sample at certain temperature ranges. In some samples, considered representative of homogeneous groups, thin section analysis to optical polarizing microscope has been performed to check more or less fine grain size and the presence of any included lithic and primary clinopyroxenes, further analysis to scanning electron microscope (SEM/EDS - Philips 515b/EDAX DX4) has been carried out to better detect phases not perceivable by the polarizing microscope (because of the fine particle size of the mixture). Subsequently, the chemical data have been processed statistically using bivariate plots and cluster analysis have been performed with the method of the average linkage to better highlight geochemical similarities of samples and to argue hypothesis of origin. During the processing of the cluster analysis, we also included chemical data of ndings of certain origin already studied (i.e. Marzabotto, Volterra, Adria, Suasa, Rimini, Faenza and Corinth), and data of three spacer rings found in the excavations of a productive area of the Etruscan town, as well as data of various clays samples carried out in the municipalities of the area (i.e. Ostellato, San Giovanni Masi and Argenta). This statistical analysis allows us to identify nine groups, mainly characterized by SiO2, Al2O3, Fe2O3, MgO, CaO among major elements and Cr, Ni, Zn, Rb, Zr among elements in trace. In all samples the predominant phase is quartz. K-feldspar is present in an amount from modest to signi cant and Plagioclase are recognized in an amount from modest to especially abundant in the samples of the Ist group. The clinopyroxenes, whose presence shows higher ring temperatures and a raw material rich in carbonates, are present in an amount from modest to abundant (Vth, VIth and IXth group). Calcite is usually scarcely present or absent in samples with high content of CaO: that confirms that the sampled findings have been baked at temperatures above 800° C, which allowed its almost complete dissociation. It was found the presence of hematite in almost all the samples in an amount from traces to modest, and also pyrite and maghemite are present in small amounts in some samples of color from light gray to dark gray: it is likely that the color is linked to the different content of these three stages, and it depends on the oxidant/reductant atmosphere to which the samples were subjected during cooking. Ist-IInd groups, identified as locally made and dated between IVth and IIInd century BC, evidently were created from raw materials poor in carbonates and elements derived from mafic rocks as ophiolite and rich in SiO2 (quartz-feldspathic skeleton). The Ist group is characterized by a homogeneous particle size and the presence of hematite which determines the characteristic red color. The IInd group demonstrates a different degree of clay purification and ring in a more reducing atmosphere. The comparison of these data with others from samples of local pottery belonging to the second half of Vth-mid IVth century BC confirms the continuity of production methods during time. The involvement in the analysis of samples of raw clay allows us to hypothesize that the deposits of raw material used for these vases were almost adjacent to the production area. The IVth group, which identified Attic pottery, comes from raw material poor in carbonates and poorer in quartz-feldspathic skeleton, but with a rich content in mafic elements. The group is rather compact in chemical and mineralogical characteristics. Analysis also confirms an Attic origin for outturned bowls and stemmed plates, vascular forms that were considered peculiar of the Adriatic and Po Valley market. Vth-IXth groups, characterized by a larger grain size than the previ- ous ones, are quite problematic. Vth-VIth groups consist of vases dating in the Vth century BC and characterized by forms predominantly of Attic influence, but their chemical-mineralogical characteristics distinguish them from Attic vases and from the remaining productions identified or used as comparison. The VIIth group is composed by a little stemmed plate, a typical local form in Spina, and by a bowl of Attic form. We could plausibly suppose that these two vases were locally made and chemically rather akin to the IInd group, thus confirming the hypothesis of a local imitation of Attic vases thanks to the bowl. We could suppose that the bowl, despite of being a close imitation of (or resembling) an Attic model, responds to a rather local request and perhaps also met an Etruscan taste in thin and sinuous vessel tectonics close to metal ware. At last, VIIIth-IXth groups are distinguished from all the others, in particular for a high content of CaO. The sample no. SVT 12, which belongs to an “Alto-Adriatico” figured oinochoe with trefoil mouth, is most likely a local product of Spina, even if the clay had a dfferent preparation from the one of Ist-IInd groups, and in particular by no. SVT 61, an “Alto-Adriatico” gured lekanis. We could divide “Alto- Adriatico” vessels at least into two productions, as noted in literature: the first one that does not differ from the black glazed pottery of the Ist group and the latter that instead has a clay rich in calcite, which may have been added to the starting raw material, likely for a whitening e ect. Finally, we would like to stress that the considerations we propose in this paper clearly show that only a systematic and multidisciplinary approach to the study of black glazed pottery supported by archaeometrical analysis can bring signi cant results not restricted only to a typological study.