Field's Chromatography

Excerpt: ... Tartarian lazur or lapis lazuli, in the course of time becoming of a dark and dismal colour. Ground smalts, blue verditer, and other pigments, have passed under the name of bice. 141. Blue Ashes, or Mountain Blue, are both hydrated carbonates of copper, the first being artificially prepared, and the second found native in Cumberland. Neither is durable, especially in oil; and, as pigments, both are precisely of the character of verditer. By treating the natural malachite green with an alkali, it may be converted into blue. 142. Blue Verditer, or Verditer, is an oxide of copper, formed by precipitating nitrate of copper with lime. It is of a 229 beautiful light blue colour, little affected by light, but greened and ultimately blackened by time, damp, and impure air-changes which ensue even more rapidly in oil than in water. It is mostly confined to distemper painting and paper-staining. 143. Egyptian Blue, called by Vitruvius, Cœruleum, is frequently found on the walls of the temples in Egypt, as well as on the cases enclosing mummies. Count Chaptal, who analysed some of it discovered in 1809 in a shop at Pompeii, found that it was blue ashes, not prepared in the moist manner, but by calcination. He considers it a kind of frit, of a semi-vitreous nature; and this would appear to be the case from Sir H. Davy obtaining a similar colour by exposing to a strong heat, for two hours, a mixture of fifteen parts of carbonate of soda, twenty of powdered flints, and three of copper. The colour is very brilliant when first made, and retains its hue well in distemper and decorative painting; but it has the common defect of copper blues of turning green in oil, when ground impalpably for artistic use. One remarkable effect of this copper smalt-for it is nothing else-is, that by lamp-light it shows somewhat greenish, but shines by day with all the brightness of azure. Mérimée believes that Paul Veronese employed this sort of...