Primary red in trichromacy and alchemical vermilion

Abstract This paper investigates a rather unexpected connection between the alchemy of vermilion, mercury sulphide (HgS), and the primary red highlighted in a colour theory that emerged in the late fifteenth century: trichromacy of colour mixtures. Some early supporters of trichromacy indeed identified the hue of vermilion as the ideal simple red they discussed in their books. The colours observed during the manufacturing of this pigment led to the alchemical colour sequence described in texts and images about the sulphur–mercury theory, and they are in some recipes the same primary colours of trichromatists. This paper also shows that the era of vermilion lasted until the late eighteenth century, when vermilion was finally rejected by other trichromatists.