“But if you don’t find any soot, take birch bark and burn it in a fire and cover this with a small pot or a glazed earthenware vessel, so the smoke must touch it. The soot that grows on it is quite good.” In: Codex Germanicus 1. 1454-1463. Hamburg, Staats-und Universitätsbibliothek, Cod. Germ. 1: fol. 73r. also in: Heiles (2018): p. 13-61.