Dissertação para obtenção do Grau de Mestre em
Conservação e RestauroThe Castro de Vila Nova de São Pedro (VNSP) is a settlement located at Azambuja, district of Lisbon, occupied during the third and second millennia BC, predominantly during the Chalcolithic period.
A diversified collection of 275 copper-based artefacts (complete or in a fragmented condition) belonging to VNSP was studied for this thesis using non-destructive and micro-destructive analytical techniques. The classification of the objects according to its main chemical elements was performed by using EDXRF spectrometry. A selection of 53 of these artefacts was analysed by micro-EDXRF spectrometry to quantify the alloy compositions. The microstructural characterisation of the metal alloys, as well as the identification of the thermomechanical processes applied to the shaping of the artefacts was accomplished through optical microscopy, supported by SEM-EDS and supplemented by Vickers micro-hardness measures to establish the actual effectiveness of the thermomechanical processes in the hardness of the artefact.
Results show that the initial collection is mainly composed of copper and arsenical copper. In the subset of 53 artefacts, 38% were considered copper alloyed with arsenic (As>2%). A statistically significant association was found between copper alloys with arsenic contents over 2% and artefacts identified as weapons. This could point out as the addition of arsenic in order to increase the weapon’s mechanical strength.
The determination of the “chaîne opératoire” by microstructural analysis show that the majority of this subset (73%) was finished with forging plus annealing operations cycles and 23% of the artefacts received final cold hammering. In several cases, the presence of arsenic rich phases in the microstructure shows no evidence of controlling cooling rates during the casting operation. No direct correlation was found between the arsenic content of the alloy and its hardness, assessed by Vickers microhardness testing. Nevertheless, proof was found of a higher hardness near the blade regions of the artefacts.Fundação da Faculdade de Ciências e Tecnologia,project METALURGIA PRIMITIVA NO TERRITÓRIO PORTUGUÊS - PTDC/HIS-ARQ/110442/200
