On the manufacture of alum, a tale I heard from the Open University on a Summer School at Durham. The recipe was acquired from a Vatican factory by spies. The Pope had the monopoly, and having just pronounced a fatwa on Elizabeth 1, buying the stuff from him was clearly a no-no. Burn the alum rich clay with seaweed. Mix the results with urine, and then boil the liquid until an egg floats in it. The alum will then crystallise out. How did they invent these processes?

Penny