A representative set of glass from mostly Indo-Pacific type beads and other materials including a carnelian bead from two Swahili sites of the Ibo Island at Northern Mozambique has been archaeometrically characterized to get insights into its likely provenance within the framework of the Indian Ocean trade networks. Selected samples were examined and analyzed by using binocular magnifying glass, field emission scanning electron microscopy with energy dispersive X-ray microanalysis, visible spectrophotometry and X-ray diffraction. Up to four different types of glasses were identified according to its chemical composition: mineral-soda alumina glass from Western India, vegetal-soda alumina glass from Central Asia, a conventional soda-lime silicate glass coming probably from Europe and a lead silicate glass of the PbO-SiO2 binary system most likely from Venice. Red and yellow colours were obtained through colloidal chromophores: cuprite micro-crystals for red brick and lead stannate and/or lead antimoniate micro-crystals for yellow, while deep blue, greenish blue and yellowish colours were obtained through ionic chromophores. Either the carnelian bead or the different types of glass are imported materials resulting from Swahili trade networks of the Indian Ocean, since no evidence of glass production or recycling has been found in archaeological fieldwork.

The authors acknowledge funding support from the following sources: the Spanish Ministry of Economy, Industry and Competitiveness through the National Program for Fostering Excellence in Scientific and Technical Research (HAR2013-48495-C2-2-P), the International Archaeological Excavations scheme from the Spanish Cultural Heritage Institute (IPCE), the Palarq Foundation, the Program TOP Heritage: Technologies in Heritage Sciences from the Regional Government of Madrid (S2018/NMT-4372), and the Spanish Ministry for Science and Innovation through the Challenges of Society program (PID2019-104220RB-I00/MCIN/AEI/10.13039/501100011033). Professional support from the CSIC Interdisciplinary Thematic Platform: Open Heritage, Research and Society (PTI-PAIS) is also acknowledged.

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Peer reviewed