Authentication of glass beads from Cultural Heritage: An interdisciplinary and multi-analytical approach

Analysis of glass-based artworks is important for authentication purposes. In recent years, there have been rapid advancements and improvements in the characterization of glass objects using different analytical approaches. The present study presents an interdisciplinary and multi-analytical authentication approach that provides useful tools and markers to unmask possible imitations, counterfeiting, and forgeries in Cultural Heritage glass beads by comparing the composition of historical and modern glass beads. The approach includes the use of binocular magnifying glass, X-ray Fluorescence (XRF), Field Emission Scanning Electron Microscopy-Energy Dispersive X-ray Spectroscopy (FESEM-EDS), UV-Vis spectrophotometry, X-ray diffraction (XRD) and Laser Induced Breakdown Spectroscopy (LIBS) techniques. Resulting data indicate that antimony, when detected, is only present in historical beads, while boron, zinc, and/or molybdenum are only detected as possible components in modern beads. As marker chromophores for historical beads, lead antimoniate or iron are responsible for yellow, copper for red, and iron and/or copper for green colors. Modern beads coloration was attributed to the presence of cadmium sulfoselenide microparticles for yellow to red colors and chromium for green colors. Opacity in historical beads was generated by dispersed tin oxide or calcium antimoniate microcrystals, while in modern beads the opacity is related to ZrO₂ microcrystals and/or fluorine ions. In this study, LIBS has been validated and proven feasible for in situ exploring analytical parameters that can be useful for authentication purposes of historical glass objects, regardless of their size, provenance, and chronology.