Beyond the earth pigments lies a more complex tradition of colour-making that requires chemical transformation of metals and minerals. These are the pigments that gave the medieval palette its most remarkable blues, greens, and whites — and they are the colours that require the most knowledge, patience, and care to produce at a time when alchemy was on the cusp of transforming into chemistry during the 17th and 18th centuries
Verditer, one of England's distinctive blue-green pigments, is produced when copper reacts with nitric acid in the presence of chalk or limestone. Historically, English verditer was a by-product of silver refining: when silver was extracted from argentiferous copper ores using nitric acid (aqua fortis) - to discover more about this illuminating period