Very early manuscripts document both the manufacture and use of vermilion. Some called this indispensable color the prince of reds which was more brilliant than the natural cinnabar. Theophilus (Roger of Helmarshausen)the Benedictine Monk, described the alchemical synthesis in his technical handbook De diversis artibus (On Divers Arts c.1122).
Sulfur and mercury, which have been sealed together in a pot, are buried in blazing coals. The Monk states, "you hear a crashing noise inside as the mercury unites with the blazing sulfur." This was a relatively new technique during the 12th century but became commonplace towards 1300 to 1400.
Source: Bright Earth by Philip Ball