afrol News, 12 April - Researchers have analysed the chemical composition and lead isotopes of the copper used in medieval West African artefacts. Despite the widespread presence of copper ore deposits in the West African region, metals used by the sophisticated metallurgical industry in sub-Saharan Africa were imported from North Africa, they found. Copper probably fuelled the trans-Saharan trade, providing North Africa with gold.
A thousand years ago, after Islam had spread into the Sahel, the trans-Sahara camel caravan trade was flowering. It has been known for a long time that mainly gold and later slaves were the most desired West African products for the Arabs at the Mediterranean coast. So far, historians have argued that salt was the main trade product brought southwards, but new research adds copper to the favourite products of West Africans in the 11th to 16th century.
At the University of Arizona (UA) in the US, a young archaeologist is analysing lead traces in ancient West African artefacts to shed light on the relatively little-understood archaeology of the region, especially the period marked by the spread of the new religion of Islam. With the introduction of Islam on both sides of the Sahara Desert, new trading opportunities were set in motion, connection North and West Africa.
Thomas Fenn, a UA doctoral student, is now unravelling evidence of these centuries-old trade patterns across the Sahara Desert by identifying smelted metal artefacts, mainly copper.
One of the questions Mr Fenn wants to answer concerns the sources of copper and other raw materials that became manufactured goods that were traded throughout the region. Specifically, why were metal workers in a sophisticated metallurgical industry in sub-Saharan Africa importing copper ingots when there were perfectly good copper ore deposits nearby?
"Knowing where these and other materials originated," says Mr Fenn, "may offer larger insights about not only trade, but also about technologies, economics and social organisation. Who controlled bankable natural resources and transportation routes? How was labour distributed in these societies?"
David Killick, a UA associate professor of anthropology and expert on the archaeology of metallurgy in Africa, holds that tracing metals is a crucial part of understanding the development of trade in medieval Africa.
"Most of the money circulating in the western half of the Islamic world between the 11th and 16th centuries was minted with gold from sub-Saharan west Africa, and competition for the wealth generated by the trade fuelled the growth of major West African [medivial empires] like Ghana, Mali and Songhai," commented professor Killick.
Using a process called lead isotope ratio analysis, or LIA, Mr Fenn has examined more than hundred Iron-Age artefacts, most of them copper, from sub-Saharan Africa. Lead has four different isotopes, three of which occur as the natural decay of uranium and thorium. The isotopic ratios change as a function of time.
Smelting does not change the ratios, making them a virtual fingerprint for a metal's source of origin. Scientists need only about 100 billionth of a gram for analysis. LIA has been used successfully to determine the sources of non-ferrous metals from sites in other parts of the world for years, but its use in African archaeology is fairly recent.
From his analysis, Mr Fenn theorises that the ore used to make the copper ornaments and other items found in the sites in West Africa likely came from North Africa. He said merchants there traded gold from regions like present-day Niger for copper from the north via camel caravans across the Sahara Desert.
Refined copper, Mr Fenn said, likely was prized as a commodity that fit in with the value system of the region, where it was easily worked into ornamental objects and other items that could be bartered for other goods and services.
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