WHEN SAM NIXON, AN ARCHAEOLOGIST with the British Museum, excavated ancient coin molds in Tadmekka, Mali, in 2005, it triggered a several-yearexploration of how medieval Africans purified the gold they were using for their currency. Nixon had found little droplets of highly refined goldleft over in the molds-which have been dated to the 11th century-as well as curious fragments of glass. Now scientists have recreated the advancedprocess behind the purification method they used then.

"This is the first time in the archaeological record that we saw glass being used to be able to refine gold," says Marc Walton, codirector of theCenter for Scientific Studies in the Arts, a collaboration between Northwestern University and the Art Institute of Chicago. "The glass appeared tobe material that was [actually] recycled glass materials ... so it really shows the industriousness and creativity of the craftsmen, who understood theproperties of gold and glass enough to [use them for] this process of refining gold." The recycled glass materials were remnants of broken vessels.Tadmekka was a town right in the middle of the trans-Saharan caravan route, so Nixon uncovered several types of material culture that had to do withtrade, namely molds for "bald dinar," or coins that hadn't been stamped with the name of a mint (or a 10th-century equivalent of one).

According to Walton, Europeans in the 10th and 11th centuries purified their gold through cupellation, a process in which lead is mixed with goldlaced with impurities, and then heated in a furnace until the droplets of purer gold can be skimmed off. But in the case of medieval West Africans,"They were taking the ore and other raw materials from the river and mixing it with glass," says Walton. Since gold is inert, it doesn't fullydissolve into melted glass, while impurities and other materials do, making this "a really novel way of using recycled glass material."

To read the complete article, see:
Medieval Africans Had a Unique Process for Purifying Gold With Glass(https://www.atlasobscura.com/articles/medieval-african-gold)