New insights on Late Bronze Age Cu-metallurgy from Coles de Samuelhoard (Central Portugal): A combined multi-analytical approach

Abstract

The hoard from Coles de Samuel is one of the largest Cu-based metal collections from the Late Bronze Age (LBA) (13th–8th centuries BC) ever found in Central Portugal, consisting of 18 artefacts which typologically display a strong regional identity. In the present study, an integrated multi-analytical approach combining Energy Dispersive X-Ray Fluorescence (EDXRF) analysis, OpticalMicroscopy (OM) and Scanning ElectronMicroscopy with Energy Dispersive X-ray spectroscopy (SEM-EDS) has been used to characterise the artefacts both from a chemical and microstructural point of view with the aim to unravel their elemental composition and technological features. Results show that all artefacts are made of binary bronze (Cu-Sn) alloys, with a Sn content in the range of 8.7 ± 0.9 and 13.0±1.0wt%,with minor elements (Pb, As and Fe) never exceeding 1.1 wt% in total. The microstructure of the vast majority of the metal objects (13 out of 18) shows the presence of equiaxial α-copper grains with annealing twins and slip bands suggesting that, in the manufacturing process, they were subjected to forging plus annealing cycles. The remains of the objects present an as-cast microstructure constituted by dendritic structures, suggesting that metals did not suffer any thermo-mechanical operation after being removed from the mould. Pb, Ag and Au-rich globules together with Cu–S and unalloyed Cu-inclusions have been observed as well, resulting from impurities from ores. The typological characterisation of these metals and their archaeometallurgical data are consistentwith an indigenous LBA Iberian metallurgical production