In Medieval Africa, A Unique Process for Purifying Gold With Glass

[Astronuc]

Medieval Africans Had a Unique Process for Purifying Gold With Glass
And scientists in Illinois have recreated it.
https://www.atlasobscura.com/articles/medieval-african-gold

Mansa Musa, emperor of Mali from 1312 to 1337, was widely known for his vast wealth in the form of gold deposits.

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. Now scientists have recreated the advanced process 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 the Center for Scientific Studies in the Arts, a collaboration between Northwestern University and the Art Institute of Chicago. “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. 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 with trade, 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).

Marc Walton's team at the Center for Scientific Studies in the Arts, a collaboration between Northwestern University and the Art Institute of Chicago, "bought gold dust from a chemical supply company, then mixed it with local Lake Michigan sand, and then made their own synthetic glass.” They heated the mixture, the minerals dissolved in the sand, which left behind the gold.”