One of the greatest missions of alchemy was to discover the philosopher’s stone, a legendary substance that was believed to turn base metals, such as lead and iron, into gold. Belief in the existence of this magical stuff goes back to at least the fourth century and obsessed alchemists well into the seventeenth. Descriptions of the stone’s appearance vary wildly, with some claiming that it is not a stone at all but a form of spiritual matter. Most accounts of how to obtain it are wrapped up in so much esoterica as to be unfathomable; those which make at least a little sense generally recommend fusing sulphur and mercury. Below is an animation of the Mutus Liber (1677), a seventeenth century book that illustrates how to make the philosopher’s stone.