Comparison of pXRF and LA-ICP-MS analysis of lead-rich glass mosaic tesserae

Laura Ware Adlington (1) , Bernard Gratuze (1) , Nadine Schibille (1)

1 IRAMAT-CEB - IRAMAT - Centre Ernest Babelon

Handheld (portable) X-ray fluorescence spectrometry (pXRF) allows for fast, in situ surface analysis, however, its application in archaeological research requires substantial optimisation. This paper investigates the matrix effects of high lead glass on the experimental results of pXRF in comparison to laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) data. 289 archaeological glass mosaic tesserae with varying lead concentrations up to 35 wt% PbO were systematically analysed by both techniques. In addition, thirteen reference glasses were analysed, including nine glass standards (BGIRA1-6 and AD1-3), which were not previously reported. The detection of low Z elements (Ca and above) was inaccurate in both low- and high-lead tesserae, due to a shallow depth of analysis and suboptimal surface conditions of archaeological glass. The presence of relatively low concentrations of lead (<0.5 wt%, depending on the element being measured) furthermore resulted in overlapping peaks. The limits of detection as well as accuracy for several trace elements were severely affected by high lead contents, leading to over- or underestimations. Separate empirical calibrations for low- and high-lead glasses were effective in correcting the data, and this approach is recommended for any study using pXRF to analyse glass assemblages, especially those containing variable concentrations of lead. We also advise that in addition to the analysis of reference materials a subset of an assemblage is analysed by another analytical technique, to assess the performance of the spectrometer and to establish a robust calibration protocol. Overall our results suggest that pXRF can be used as a survey technique to differentiate compositional groups and inform further sampling. Even though the identification of specific glass groups requires major element compositions, different primary glass types and colouring/opacifying techniques can be discriminated.

Mots clés: High lead glass; handheld XRF; Surface analysis; LA-ICP-MS; Archaeology

Domaines: Archéologie et Préhistoire; Matériaux; Chimie analytique

Laura Ware Adlington, Bernard Gratuze, Nadine Schibille. Comparison of pXRF and LA-ICP-MS analysis of lead-rich glass mosaic tesserae. Journal of Archaeological Science: Reports, 2020, 34, Part A, pp.102603. ⟨10.1016/j.jasrep.2020.102603⟩. ⟨hal-02967327⟩