Take the ravenous grey wolf that on account of his name is subjected to bellicose Mars, but by birth is a child of old Saturn, and that lives in the valleys and mountains of the world and is possessed of great hunger. Throw the king’s body before him that he may have his nourishment from it. And when he was devoured the king, then make a great fire and throw the wolf into it so that he burns up entirely; thus will the king be redeemed.
That’s some instructions by Basil Valentine, from 1602. Principe explains that this is a real experiment: the king is gold; the wolf is melted stibnite, or antimony ore. A 14-karat gold ring is 58% gold, 42% copper. Throw it in melted stibnite and it dissolves. The copper turns into a sulfide, while the gold and antimony meld together and sink to the bottom, where they can be easily retrieved. Roast this mixture and the antimony evaporates, leaving you with pure gold. So this is an obfuscated but correct recipe for purifying gold.
Medieval alchemists might have had something like this: