"...According to Walton, Europeans in the 10th and 11th centuries purified their gold through cupellation, a process in which lead is mixed with gold laced with

"...According to Walton, Europeans in the 10th and 11th centuries purified their gold through cupellation, a process in which lead is mixed with gold laced 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 fully dissolve into melted glass, while impurities and other materials do, making this “a really novel way of using recycled glass material.”....."