Elemental characterisation of a collection of metallic oil lamps from South-Western al-Andalus using EDXRF and Monte Carlo simulation

Abstract

This study is part of a wide-scale research on metal production in South-Western al-Andalus during the Islamic period, under the project “DE RE METALLICA - DEfining and REdiscovering MEtallurgy and Trade in AL-Andalus (8th–13th centuries AD): Leaping into Innovative Comprehensive Archaeometric Approaches”. In particular, this paper presents the results of the elemental analysis carried out on a group of six Islamic oil lamps found at different sites in Southern Portugal, spanning from the 10th to the 13th centuries AD. Due to the exceptional historical value of these artefacts, the analyses were carried out according to a completely non-destructive approach that combines Energy Dispersive X-ray Fluorescence Spectrometry (EDXRF) with a Monte Carlo (MC) simulation code named X-ray Monte Carlo (XRMC). This novel and ground-breaking approach has proven to be especially suitable for non-destructive analysis of artefacts with a multi-layered structure, such as archaeological metals, being able to estimate the composition of the original alloys and to characterise the structure and composition of each layer superimposed to the bulk with no need of removing samples or cleaning the artefacts’ surface from corrosion compounds. The application of the EDXRF/MC analytical protocol revealed that the six oil lamps selected for this paper are covered by a structure composed of three different layers (protective layer + corrosion patina + alloy). The bulk metal is a copper-based alloy with a great variability in terms of Fe, Zn, Sn, As, and Pb, likely suggesting either the use of scrap metals as raw material or the indiscriminate addition of different kind of minerals. With regard to the objectives of this paper, EDXRF/MC protocol successfully allowed to estimate the chemical composition of the six oil lamps in a completely non-destructive way, thus representing a viable compromise between the necessity to ensure their physical integrity and the need to obtain reliable analytical data able to address historical issues.