Use of Zanzibar copal (Hymenaea verrucosa Gaertn.) as incense at Unguja Ukuu, Tanzania in the 7-8th century CE: chemical insights into trade and Indian Ocean interactions

This study presents the chemical analysis of an amorphous organic residue extracted from a 7th-early 8th century CE brass artefact from the trading port of Unguja Ukuu, Zanzibar, Tanzania, hypothesised to be an incense burner. The artefact is a very rare and highly significant find in East Africa, with only one other example being found previously (also at the same site), and likely represents early contact between coastal East Africa and the Indian Ocean world. Chemical analysis of the residue adhering to this artefact was undertaken to confirm its use to burn incense, and to determine whether the resin used was local or exotic to East Africa and thus likely acquired through long-distance trade. The residue extract was analysed by gas chromatography-mass spectroscopy (GC-MS) and identified as Zanzibar copal (. Hymenaea verrucosa Gaertn.), a local species that rose to major importance in colonial period trade. The results obtained from this study provide the first direct archaeological evidence for the ancient use of this East African species as an aromatic, suggesting that it might have had a much earlier role in long-distance incense trade than previously demonstrated. This finding also provides insights into local East African engagement with the material culture of the Indian Ocean world.