Inclusions and metal composition of ancient copper-based artefacts: A diachronic view by micro-EDXRF and SEM-EDS

A diachronic view of the metallurgy in the Portuguese territory during the first three millennia after its appearance in the Iberian Peninsula is presented based on the current state of the art. Results of micro-energy dispersive X-ray fluorescence (micro-EDXRF) analyses made on metal artefacts to determine their composition and scanning electron microscopy with energy dispersive analysis (SEM-EDS) analyses to study microstructural features as inclusions are shown to illustrate trends and specificities of each chronological period. Generally, in early periods, namely during the Copper Age and first stages of the Bronze Age, unalloyed copper and arsenical copper were at use, and only by the Late Bronze Age (LBA) did tin bronze substitute almost completely the previous role of copper. In the Early Iron Age, during the Orientalising period, a general decrease in the average tin content in bronzes seems to happen. Regarding the inclusions observed in the metal matrix, these seem to suffer a diversification with the appearance of tin bronzes. By the Copper Age, only CuO and CuAsO inclusions are observed, while by the LBA CuS inclusions become regular, besides others less frequent, as SnO, CuSFe and Pb globules. Overall, with the present analytical study, the complementary character of micro-EDXRF and SEM-EDS in the study of ancient metals is demonstrated, providing a first general overview of the ancient metallurgy at the Portuguese territory which is of key importance to specific investigations of the future.