Three different metallurgical collections were studied in the present thesis. The collections originated from Chalcolithic settlements in the Portuguese Estremadura region, namely Vila Nova de São Pedro (VNSP), from where the largest group belongs, Moita da Ladra (ML) and Outeiro Redondo (OR). These studies aimed to provide a general view of the early metallurgy in the Estremadura region, as well as detailed information on the metallurgy of each archaeological site. Several analytical methodologies were involved, namely energy dispersive X-ray fluorescence spectrometry (EDXRF) and micro-EDXRF to determine elemental compositions; optical microscopy and scanning electron microscopy with X-ray microanalysis for microstructural characterization, and hardness and colour determinations of the alloy.
The main results indicate that metal was produced only in VNSP, using a crucible technology and working under poor reducing conditions during smelting operations. These conditions would result in highly viscous and heterogeneous slag and high retention of metal prills. On the other hand, artefact production was most likely accomplished in all three settlements. Artefacts were composed of copper or copper with arsenic (As ≥ 2 wt.%), being the iron content below the quantification limit (< 0.05 wt.%) in most cases. The higher percentage of arsenic content of the artefacts recorded at ML is possibly related to the diversification of exploited ore deposits, including the OMZ and the Iberian Pyrite Belt. This diversification was likely due to the shorter and later chronological occupation period (Bell Beaker Phase) of ML and OR, compared to VNSP. The increased use of copper alloys with higher arsenic contents was not observed in OR possibly due to the small artefact collection. Also, despite ML and OR being contemporaneous, the presence of the Bell Beaker period was stronger in ML than in OR. In the case of VNSP, the percentage of arsenical copper artefacts seems to be significantly inferior from ML and OR. The existence of metallurgical activities in VNSP for a longer time interval may cause higher variability in the arsenic content of the alloys as a consequence of several recycling cycles over time. The thermomechanical processing was found to be similar in all three settlements, consisting of one or more cycles of hammering and annealing, with a final forging procedure applied in less than half the artefacts in all collections. Results also suggest that colour was probably the main property determining the selection of the arsenical alloys by ancient metallurgists rather than their mechanical properties.
The occurrence of the cubic arsenide in these particular objects suggests that it was precipitated due to long-term ageing at room temperature, which points to the need of a redefinition of the Cu-As equilibrium phase constitution. These results highlight the importance of understanding the impact of structural ageing for the assessment of original properties of archaeological arsenical copper artefacts, such as hardness or colour
