Green Pigments. These are numerous and some are very important. Several of them are mechanical mixtures of blue and yellow; a larger number are chemical compounds which are naturally green; but of either kind only a few are extensively used. All those which are serviceable or have any special interest are noticed in what follows.
Sap green is the only one of vegetable origin that need be mentioned. It is prepared from the gummy juice of the berries of a species of buckthorn (Rhamnus catharticus), and is a fine transparent yellowish-green. It is unfortunately fugitive, but is occasionally employed in water-colour painting.
Terra verde is a kind of ochre. This pigment is much used by artists for painting in oil, being one of the most permanent greens. It has not much body, but can be mixed with other colours without injurious results.
Oxide of chromium, like the last, is found native, but for use as a colour it is always artificially prepared. It is a sober, permanent green much liked by some landscape-painters. Viridian and Veronese green are also oxides of chromium, but the latter is often adulterated with arsenic.
Emerald green (cupric aceto-arsenite).—This very bright (but poisonous) green, also called Schweinfurt green and Paris green, is employed to a limited extent by artists and decorators, and is used as an insecticide.
Secheel's green (cupric arsenite) is another bright green, although not so vivid in colour as the last, which it resembles in stability and in other properties. This is a dangerous pigment, and is unfortunately a good deal employed for colouring paper-hangings, artificial leaves, and toys.
Brunswick Green.—Several distinct pigments are known by this name. One of the kinds employed by the house-painter is a basic carbonate of copper, mixed with gypsum or other bodies. It is fairly permanent. Mountain green, mineral green, and malachite green are also carbonates of copper. In chemical books Brunswick green is usually said to be the oxychloride of copper. Chrome green, noticed below, is likewise called Brunswick green.
Rimman's green, known also as zinc green and cobalt green, consists of 88 per cent. of oxide of zinc and 12 per cent. of protoxide of cobalt. This colour is permanent, and is not affected by strong heat.
Chrome green is a mixture of chromate of lead and Prussian blue. It is a bright, strong colour, and is suitable for ordinary mechanical painting. It is, however, not permanent; a more durable green, but one of less power, being formed with French ultramarine and chrome yellow.
Hooker's green is a mixture of Prussian blue and gamboge, and possesses some permanence as a water-colour. Prussian green is formed in the same way, but contains more blue.
Greens which are compounds of copper are all more or less poisonous even when they do not also contain arsenic.
Artists generally prefer to make up the shade of green they require by mixing blue and yellow pigments for bright shades, and blue and brown colours for dull shades. As a rule the green portions of pictures have stood the effects of time worse than other colours.
For the materials used in dyeing textile fabrics green, see DYEING and CALICO-PRINTING; and for green colours used in painting or printing pottery, see POTTERY.