A study of 11th–15th centuries AD glass beads from Mambrui, Kenya: An archaeological and chemical approach

Twenty-three 11th–15th centuries AD glass beads collected from the archaeological site of Mambrui in Kenya were analysed using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS). The results show that all of the glass samples are soda-alumina-silica glass. They belong to the mineral soda- alumina (m-Na-Al) glass type, characterised by high alumina and relatively low calcium and magnesia contents, that was widely distributed in eastern and southern Africa and southeast Asia in the 5th century BCE – 19th century CE. They were made with a mineral alkali flux called reh and sand. Comparison with contemporary m-Na-Al glass beads from Africa and southeast Asia shows that all of the Mambrui glass beads share similar characteristics to m-Na-Al 6 glass. This new glass type was recently identified by Dussubieux and Wood (2020) and is characterised by elevated levels of U (avg. 60 ppm) and Cs (~1.5 ppm). It is commonly found in eastern African sites such as Manda and Gede in Kenya. The lead isotope results suggest that the Mambrui glass beads might have been coloured using lead sources from four different sources including ores from India and northern Thailand.