Mining, Metals and Manillas in the Atlantic Slave Trade: Pilot Study

By Prof. Dr. Paul Basu and Dr. Tobias Skowronek

Between the 15th and 20th centuries, hundreds of millions of species known as manillas were shipped from Europe to West Africa. These open horseshoe-shaped rings made of metal have been traded for the enslaved, as well as gold, ivory, palm oil, and many more commodities.

However, despite the enormous industrial scale of their manufacture, alarmingly less is known about both their production in Europe and their consumption in West African markets. Recent advances in the studies of 16th-century manillas, so-called “tacoais” by geochemical characterisation, have revealed the untapped potential for historical research. Comparing trace elements and lead isotope ratios of tacoais manillas and the renowned Benin Bronzes showed a striking similarity, indicating that the tacoais manillas were indeed used as a source of raw material for casting the Benin artworks.

However, the further development of manillas manufacturing in Europe and their use in West Africa still needs to be explored, including the unknown sources of raw materials, involved actors, and their trade networks. While central European copper sources were used to trade goods in the earlier periods, from the beginning of the 18th Century, copper from the Americas was imported to foundries in Britain.

It remains unclear whether this copper was used for making trade goods such as manillas as chemical databases for later types, referred to as “popo” and „Birmingham“ manillas, which do not yet exist. Establishing a connection between the colonial exploitation of copper ores in the Americas and the production of these trade goods for the West African trade in Europe might highlight global dependencies within these transatlantic economies and thus further point to the complexity of trade relations in this period.

Casting a first glance at these trade systems’ geochemical analysis of distinct types of “popo” and “Birmingham” manillas can lead to new insights regarding raw material choices. The collection of Prof. Dr. Rolf Denk in Rüsselsheim offers the chance to take a first look at these manillas.

Lead isotopy and trace elemental analysis are helpful for understanding their raw material sources. While lead isotopy may point to the origin of the lead used for alloying them, trace elemental analysis can help understand the copper source and its manufacturing.

For these investigations high resolution inductively coupled mass spectrometry (ICP-MS) analysis is carried out at the research laboratory of the Deutsches Bergbau-Museum in Bochum, Germany, using both a Thermo Bremen Neptune XT for measuring isotopes and a Thermo Scientific Element XR for measuring trace elemental compositions.

The results will help us understand both the production processes and the raw materials used in their fabrication and thus further supplement the chemical database necessary to understand the nature of West African artworks.

The pilot project will strengthen a developing collaborative relationship between University of Bonn and Technische Hochschule Georg Agricola (THGA) in Bochum, with its world-leading archaeometallurgical research facilities, and provide data that will support a more ambitious research project that we are planning with Dr Tobias Skowronek.

The Global Heritage Lab and the Bonn Center for Dependency & Slavery Studies of the University of Bonn financed the material analysis.