Chemical analysis of glass beads from Igbo Olokun, Ile-Ife (SW Nigeria): New light on raw materials, production, and interregional interactions

The site of Igbo Olokun on the northern periphery of Ile-Ife has been recognized as a glass-working workshop for over a century. Its glass-encrusted crucibles and beads were viewed as evidence of secondary processing of imported glass until the high lime, high alumina (HLHA) composition of the glass was recognized as unique to the region. Archaeological excavations conducted at Igbo Olokun recovered more than twelve thousand glass beads and several kilograms of glass-working debris. Fifty-two glass beads from the excavated assemblage were analyzed by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) and scanning electron microscopy-energy-dispersive X-ray spectroscopy (SEM-EDS) to understand the chemical characteristics of the Igbo Olokun glass beads in comparison with previously analyzed beads. The analyses affirm the prevalence of HLHA glass beads, and provide firm evidence of a new compositional group characterized by low lime, high alumina (LLHA); no imported soda-lime glass beads were among the analyzed samples. The evidence from crucibles indicates that LLHA glass was worked together with HLHA glass at Igbo Olokun and may have been made locally as part of the same technological tradition. Most likely, granitic sand with or without added calcium carbonate was used to produce these two types of glass, and colorants rich in MnO, Fe2O3, CuO, and CoO were intentionally added. Its occurrence in other West African societies, and the presence of some soda-lime glass beads in other sites in Ile-Ife suggest that Ife was involved in regional and inter-regional networks during the early to mid 2nd millennium AD and possibly earlier