Alchemy is the process of turning base metal into gold. For Jonson, it was also characterized as the pursuit of the Philosopher’s Stone (which could be a liquid), the thing that would effect or catalyze the transformation. The name comes from a place called Al-Kemia, the Black Land or Egypt, perhaps named after the black soil of the Nile.
Alchemy disappeared after the fall of Rome and reappeared in 12th century Europe, and was translated from the Arabic into Latin. Alchemy is the forerunner of chemistry, and one of the world’s scientists, Isaac Newton, made many secret alchemical investigations.
One of the central principles of alchemy as it is addressed in The Alchemist is that the transmutation cannot be achieved unless the person carrying it out is completely pure, completely expert, and completely pious. The alchemist “could not make gold until he had ceased to want to do so,” according to contemporary literature. This is why Epicure Mammon has to find someone who does not desire gold himself to craft the Philosopher’s stone on his behalf, for he is too lustful and covetous to be able to do it himself.
Also central to alchemy is the idea that everything is in a constant state of flux, which means that one thing can very easily become another. Just as the egg can hatch into a chicken, lead, under the right conditions, might easily turn into gold. Twelve stages of the process were imagined, identified by different colors (see the beginning of Act 2, Scene 2) and all with different names. All of this is almost totally in line with contemporary accounts when it is described by Subtle in his great speech in Act 2, Scene 3, lines 141-76.
Of course this idea of transformation is central not just to the alchemical process but also to the way that Face and Subtle can turn base substance into gold by tricking their gulls. It is similarly important to the ease with which Face and Subtle can “become” other characters. Alchemy is more than a scientific idea here; it provides Jonson with a multiplicity of rich metaphors for change and for wealth.