The Goldilocks Moment: Fire, Material Change, and Critical Time in Medieval Metallic Transmutation

In medieval Latin alchemy, "the work" (<i>magisterium</i>) in the laboratory paralleled the work of nature - yet while nature took over "a thousand years" in the mine, the artifex in the laboratory would only need "a month, or a shorter, or longer time." The amount of time needed was dependent on the degree of heat of the fire. A higher degree of heat (<i>calor ignis forti</i>) would speed up the process, while baking the given preparation over a slow, gentle fire (<i>suaviter</i>) prolonged it. This paper argues that for medieval Latin alchemists, the accomplishment of the magisterium depended on finding the precise moment to take away the product from the fire, by regulating the intensity of fire and observing natural signs. While ancient alchemy saw success linked to an astrological "favourable moment" chosen for the <i>beginning</i> of the work, medieval Latin alchemy brings a more naturalistic focus on figuring out what I call the "Goldilocks moment": the exact moment of ripeness at the end of the work, beyond which the action of fire would naturally become destructive. The paper examines this practical philosophy of fire and its relationship with time in material transformation in Petrus Bonus' <i>Pretiosa margarita novella</i>.