The Reliquary Bust of Saint Lambert from the Liege Cathedral, Belgium: Gemstones and Glass Beads Analysis by pXRF and Raman Spectroscopy

The reliquary bust of Saint Lambert, hosted in the Treasure of the Liege Cathedral, was produced in the early 15(th) century. This exceptional goldsmithery piece is covered with gold-coated silver, and decorated by approximately 400 stones, analysed by Raman and pXRF techniques to determine their mineralogical and chemical composition. The results confirm the identification of one hundred pearls, twenty-six rock crystals, ten amethysts, two diamonds, and numerous glass beads with a green, blue, colourless, turquoise, orange or red colour. The glass beads show a soda-lime composition, confirming that they are contemporary of the bust and imported from Venice, as reported by historical sources. Orange beads show a lead composition and the red stone a triplet with quartz, indicating that they were added to the bust later. The cutting of gems and beads shows also a significant evolution. The metal contains approximately 60% of Au and 40% of Ag. The origin of gemstones was difficult to establish, due to the absence of characteristic trace elements, but the chemical elements used for the manufacture and colouring of the beads were determined. This study confirms the trade of stones between Liege and Venice during medieval times.