Multi-analytical charaterization and multivariate analysis of Spina slags: Insights into polymetallic production and furnace conditions

The Etruscan harbor of Spina (Ferrara, Italy) was a major Adriatic trading center during the 5th - 4th century BCE in the Mediterranean, whose technological activities remain only partially understood. Although its commercial role is well-documented, the organization, scale, and technological features of local metallurgical dynamics activities remain poorly constrained (Sassatelli & Govi, 2013). This study presents a multi-analytical archaeometric characterization of slags recovered during the 2023 excavation, aimed at reconstructing key steps of the site’s “chaîne opératoire” (Rehren & Pernicka, 2008). A representative set of samples was investigated through an integrated protocol combining digital microscopy for morphological screening (Hirox), extensive portable XRF (pXRF) chemical mapping, and microstructural analysis of polished thin sections. Mineral phases were identified using Optical Microscopy, SEM-EDS, and Micro-Raman Spectroscopy. The investigated assemblage points to a complex polymetallic production system, documented by the cooccurrence of iron-rich slags containing magnetite and hematite and residues related to copper-processing residues (Chiarantini et al., 2018). The occurence of well-developed, idiomorphic mineral phases within the glassy matrix, suggests specific cooling histories and poits to a degree of control over melt properties during both ferrous and non-ferrous operations. Relict quartz and K-feldspar crystals may reflect contributions from furnace linings ceramic materials, or fluxing agents, whereas the vitrification of associated ceramics supports the attainment of high-temperature conditions. From a preservation perspective, the widespread calcite infilling observed within pore spaces are interpreted as a secondary post-depositional product related to the hydromorphic conditions of the Po Delta environment. Distinguishing these secondary alteration phases from the primary mineralogical assemblage is therefore essential to avoid misinterpretations of the original smelting recipes and fluxing strategies. In conclusion, the results point to a high degree of metallurgical expertise at Spina, including the ability to manage furnace atmosphere and redox conditions. The dataset, integrating mineral chemistry and microstructural descriptors, is currently being explored through principal component analysis (PCA) to identify “technological patterns” and assess possible links with raw material selection and provenance. This approach provides a refined framework for interpreting metallurgical practices the Po Valley’s archaeological heritage.