Glass Beads from Songo Mnara, Tanzania:Chemical Composition and Evidence for Local Bead Manufacture

The fourteenth-to-sixteenth-century AD site of Songo Mnara, in the Kilwa archipelago in southern Tanzania, is a stone town with many standing coral buildings. Extensive excavations at the site have produced over 9,000 beads, 7,444 of which are glass. A subset of 140 of these was chemically analyzed using laser ablation-inductively coupled plasma-mass spectrometry, revealing a notably diverse assemblage that included four main glass types: mineral soda-high alumina (m-Na-Al), vegetable soda-high alumina (v-Na-Al), high lead glasses, and vegetable soda-lime (v-Na-Ca) glass. Here we present these types, giving the first tightly dated assemblage for the fifteenth-century coast. We then focus on two notable features of the assemblage. Among the high-lead glass beads are two types from China: one dates to the early fifteenth century and the other from about 1600. These later Chinese beads were accompanied by some of the earliest European beads (v-Na-Ca) found in eastern Africa. Their provenance and meaning are examined. Then, we discuss large folded beads that were decorated with trails of colored glass. Such beads have been recorded only at Songo Mnara and Kilwa Kisiwani, and we suggest they may have been made locally from imported v-Na-Al glass.