XAS study of etched carnelian beads from the British Museum Collection: investigating the chemical contribution of the whitening

Etched carnelian beads are important archaeological artefacts that were produced from the Early Bronze Age and spread through commercial and technological exchanges all across Eurasia. Their characteristic patterns were drawn by craftspeople using a caustic paste that etched the areas of the plain Fe-coloured carnelian on which they were applied, turning them white when heated. Despite their bold white colour, the etched areas have been found to display an increased porosity compared to the unetched ones, without any compositional difference. Here, we propose to use Fe K-edge µ-XAS (ID21) to study a set of ancient carnelian beads from the British Museum collections and mock-up samples to further understand the origin of the white colour of the etched beads, as well as assess the possibility to characterise the manufacturing process of such beads with this technique.