This article leaves me super unclear on the metallurgical process going on here--you fire gold ore on a bed of glass rubble and the impurities are adsorbed into the ceramic or ???
A whole lot of chemistry process is just X dissolves in Y but not in Z, and using that in order to separate and purify.
In this case metal oxides dissolve in glass (sand, which is a silicon oxide, mostly) but gold doesn't A) oxidize under reasonable conditions or B) dissolve in the glass. Sand or glass waste is melted, the not gold dissolves into the molten glass.
