Cr2O3.2H2O - A permanent green pigment composed of hydrated chromium oxide. Viridian is a synthetic pigment with characteristic deep green, transparent particles which are unaffected by light and chemicals. Viridian, though not extremely popular because of its high price, was used as a pigment in all types of binding media. The process for making the hydrated form of chromium oxide was discovered in 1838 by Pannetier in Paris. A less expensive method for manufacturing viridian was patented by Guignet in 1859. Viridian has been commercially available since the mid 19th century. It is stable in all media. The pigment is also used as a colourant in concrete mixtures. Synonyms: Pigment Green 18; CI 77289; transparent chrome oxide; chromium oxide green transparent; vert emeraudé (Fr.); French Veronese green; Pannetier's green; Mittlers' green; Guignet's green; chromic hydroxide. Museum of Fine Arts, Boston (2000); Trench (2000). [J. Cassar, R. de Angelis]