The concept of the Philosopher’s Stone (Latin lapis philosophorum), current in literal and metaphorical senses since the beginning of the early modern period (e.g. Angelus Silesius in the 17th century), was central to alchemy. It concerned the possible existence of a particular substance capable of transforming base materials into precious ones, and metals ultimately into gold, by triggering their inherent tendency to perfection. Producing the Philosopher’s Stone, in what became known as the “great work” (opus magnum), was discussed in countless practical guides …