Glass Beads from Medieval Gao (Mali): New Analytical Data on Chronology, Sources, and Trade

Excavations at several archaeological sites in and around Gao have resulted in the recovery of thousands of glass beads presumed to have been acquired from glass bead-producing centers through trade. The bead assemblages cover the period from the eighth to the fourteenth century CE. Here we report on the results of compositional analysis by LA-ICP-MS of 100 beads, permitting comparison with the growing corpus of chemical analyses for glass from African and Near Eastern sites. In this analysis, several compositional groupings are recognized. These include two types of plant-ash soda-lime-silica glass (v-Na-Ca), a mineral soda-lime-silica glass (m-Na-Ca), a high-lime high-alumina (HLHA) glass, a mineral soda-high alumina (m-Na-Al), glass, a plant ash soda-high alumina (v-Na-Al) glass and a high lead composition glass. The reconstruction and dating of depositional contexts suggests a shift in glass sources at the end of the tenth century CE. The issue of source identification is discussed and occurrences at other African sites are mapped, providing new data towards an understanding of trade and exchange networks.