Research on the Glass Beads from the Nanhai I Shipwreck: A Potash-lead Glass Bead Technological Tradition Originating from Han Dynasty Lingnan

To gain deeper insights into the manufacturing techniques and raw material sources of the glass beads collected from the Nanhai I shipwreck dating from Southern Song Dynasty, a comprehensive analysis was conducted on three typical types of beads using digital microscopy, X-ray micro-computed tomography (Micro-CT), micro X-ray fluorescence spectrometry (μ-XRF), laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) and micro-Raman spectroscopy. The results indicate that these beads are typical Chinese potash-lead and lead silicate glasses, manufactured primarily using the coiling technique. The opaque yellow coloration was obtained with the use of lead stannate (lead-tin yellow type II) as both a colorant and opacifier. The black glass beads also contain high levels of tin, while those with orange interior was colored by the combined use of Cu2O and CuO. The black beads exhibit signs of weathering from the presence of such corrosion products as Pb2CO3Cl2, PbSO4, and 2PbCO3·Pb(OH)2. The technological lineage of these potash-lead beads is discussed below from the perspectives of their compositional system and the nature of the opacifiers that were used, linking them to Han Dynasty potash-lead glass from Lingnan. Based on the results of trace element and lead isotope analysis, the provenance of the raw material used to these glass beads was also investigated.