Two forms of yellow-orange arsenic sulphide
Closely related to orpiment, realgar (α-As4S4) can easily transform to pararealgar (β-As4S4) as a result of a light-induced transition. This means that the change can take place on a manuscript's page, resulting in frequent identification of the two together. Rather uncommon pigments, these arsenic sulphides were favoured by Venetian painters and illuminators in the late 15th and throughout the 16th century.
Arsenic sulphide pigments - orpiment, realgar and pararealgar - cannot be easily distinguished with the analytical methods used for this project, with the exception of Raman spectroscopy. Therefore, in cases where Raman spectroscopy was not used to analyse a certain manuscript, the pigment is identified only as an 'arsenic sulphide', with no further specification.
