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Emerald Green

Synonyms: Emerald Green, Cupric Aceto-Arsenite, Schweinfurt Green, Vert Paul Vérončse, Schweinfurter Grün

This pigment was discovered in 1814 during the course of experiments made with the object of preparing an improved Scheele's green. It may be prepared by half a dozen slightly differing processes, but in all verdigris (or vinegar and blue vitriol) and white arsenic are the two essential materials employed. Generally verdigris is dissolved in acetic acid, and added to a boiling aqueous solution of white arsenic: on continued ebullition a deposit of emerald green occurs. Sometimes copper sulphate, potassium arsenite, and acetic acid are employed. Whatever the method, it is necessary that the coloured product be washed with boiling water to remove the last traces of soluble salts.

The hue of this pigment is a nearly normal green, slightly verging upon bluish green; it is brighter and more opaque than Scheele's green, and, like it, is a deadly poison. It is less attacked by sulphuretted hydrogen than Scheele's green, but as a water-colour, does not long remain untarnished in impure air. In oil it is practically permanent, both alone and when used with the majority of permanent pigments. It is, however, quickly blackened by the cadmium yellows. Emerald green cannot be relied upon as permanent in fresco and tempera painting. Its use in wall papers and in the decoration of all domestic furniture and fabrics is to be deprecated, by reason of its poisonous character; but is, happily, at the present time, in great measure abandoned.

Emerald green, if pure, dissolves perfectly in boiling dilute nitric or hydrochloric acid; the solutions thus made should yield no precipitate with a few drops of barium chloride solution. An undissolved residue generally shows the presence of baryta white.

Emerald green may be distinguished from Scheele's green by a simple experiment. If a small pinch of the dry powder be warmed with a few drops of moderately strong sulphuric acid (half oil of vitriol, half water), acid vapours, having the smell of vinegar, will be given off only when true emerald green is the subject of the experiment.

On the Continent, Vert Émeraude is the name given to viridian, the emerald oxide of chromium.


Last Update: 2011-01-23