The study of alchemy moved from Byzantine Egypt in then first centuries AD to the Arab caliphates in the Early Middle Ages and then to the West during the High Middle Ages, continuing well into the Age of Enlightenment.
Over this span of time, alchemists slowly began to reach concensus on the formation of the philosophers' stone, which they called the magnum opus (the great work).
Supposedly, the alchemist first created a black substance in a process called nigredo, identified with Aristotle's prime matter. Then, through a process called albedo and rubedo, a white and then a red stone form that can transmute metals into respectively silver and gold.
Unfortunately, this whole process is a fiction, yet many claimed to have made the stone and various accounts are known of scam artists pretending to make it.
"The Great World History Book"