Raman and XRF classification of Asian and European glass beads recovered at Mutamba, a southern African Middle Iron Age site

Abstract

Twenty-eight representative beads found at the thirteenth-fourteenth century AD site of Mutamba in southern Africa were classified morphologically and then analysed with pXRF. Eighteen beads were selected from four identified series of K2-IP, EC-IP, Mapungubwe Oblate and European for Raman spectroscopy. The results show corrosion has a great effect on the composition and nanostructure of Mapungubwe series with lixiviation of alkalis. In corroded K2-IP beads elevated amounts of potassium recorded on the surface layer compared to less corroded IP beads. Despite these changes pXRF and Raman spectroscopy were successful in discriminating of the bead series by considering the concentration of trace elements (Zr, U), detected pigments (lead tin yellow (II), red lead), opacifiers (SnO2, calcium antimoniate) and colorants (Fe, Cu, Co) and their concentrations in the beads.