When Sam Nixon, an archaeologist with the British Museum, excavated ancient coin molds in Tadmekka, Mali, in 2005, it triggered a several-year exploration of how medieval Africans purified the gold they were using for their currency. Nixon had found little droplets of highly refined gold left over in the molds—which have been dated to the 11th century—as well as curious fragments of glass. “The glass appeared to be material that was [actually] recycled glass materials … so it really shows the industriousness and creativity of the craftsmen, who understood the properties of gold and glass enough to [use them for] this process of refining gold.” The recycled glass materials were remnants of broken vessels. 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. To get to the bottom of how medieval Africans purified gold so successfully, they also made do with what their environment provided them.