On the Use of the Unusual Green Pigment Brochantite (Cu-4(SO4)(OH)(6)) in the 16th-Century Portuguese-Flemish Paintings Attributed to The Master Frei Carlos Workshop

摘要

This paper reports an unusual green pigment, brochantite (Cu-4(SO4)(OH)(6)), on 16th-century Portuguese-Flemish paintings, attributed to the Master Frei Carlos workshop. This green mineral is usually identified as an impurity or alteration product in the green pigments verdigris (Cu(CH3COO)(2) nCu(OH)(2)) or malachite (CuCO3 Cu(OH)(2)). However, after thorough investigation with a broad range of analytical techniques, it became clear that, in this case, brochantite was applied as a pigment. The abundance, pigment granulometry, and pigment morphology suggest intentional use by this Portuguese-Flemish Master as a natural pigment rather than its accidental use as an alteration product. This seems to be a distinguishable feature to other painters (Flemish and Portuguese) working in Portugal at the beginning of the 16th century.