Vermilion: Cinnabar - Vermilion - Zinnober.

The mineral cinnabar, or mercuric sulphide, occurs in many parts of Europe, and abundantly in China, and is extensively worked in New Almaden in California; it would be tedious to recount the numerous localities in which it has been, or is, found. Its colour in the mass varies from cochineal-red and red-brown to lead-grey; its powder is usually scarlet, or red. Its hardness lies between that of gypsum and that of calc-spar. It seldom contains even 1 part in 100 of impurities, but consists in 100 parts of very nearly 14 parts of sulphur by weight, united with 86 of mercury, or 1 atom of each element. The density of native vermilion is about 9. Vermilion was formerly known as vermiculus, cinnabaris, ceno-brium, and minium; the last name is now appropriated to red lead. Vermilion and vermiculus are derived from the Latin vermes, a name originally designating the 'kermes' insect found on the ilex or evergreen oak, which is still used for the preparation of a red dye. From kermes, in its turn, the words crimson and carmine are derived.

The name cinnabar is supposed to be of Oriental origin (compare the Persian zanjifrah), and was used sometimes to designate dragon's blood, a red resin.

Theophrastus informs us that two kinds of cinnabar were known to the Greeks. One of these was undoubtedly real cinnabar (chiefly from Spain), the other was red lead. Pliny's 'cinnabar' or 'minium' was true vermilion, so was the 'minium' of Vitruvius. Theophilus calls it 'cenobrium,' Wyclif 'cynoper,' Hakluyt 'cinaper,' and Ben Jonson 'cinoper.'

One of the most curious facts concerning vermilion is that it is identical in the nature and proportion of its two constituent elements with an artificial black substance, 'Æthiop's mineral.' The red substance may be changed into the black, and vice versâ, and this without any loss or gain, or any alteration of chemical composition, the change being a physical or molecular one merely. The black substance is amorphous, the red crystalline.

The pigment vermilion may be made by simply grinding selected pieces of native cinnabar, or it may be obtained artificially by combining the two elements sulphur and mercury.

All the methods of preparing vermilion artificially may be grouped under two divisions. The first of these is the dry way, the other the wet way. In the former method metallic mercury 42 parts, and sulphur 8 parts, are intimately mixed and agitated together in revolving drums until they have combined. The brownish-black powder thus obtained is then submitted to sublimation in vertical iron cylinders, surmounted by heads which are connected with receivers. On sufficient heating, the mercuric sulphide sublimes as cinnabar or vermilion, the best part condensing in the retort-heads. The rest of the sublimed product (which has travelled farther) contains free sulphur, and is of inferior colour. The selected portions are next ground, moistened with water, warmed with a little caustic potash solution or nitric acid, and then thoroughly-washed with boiling water. In another dry process the mercury is gradually added to the proper proportion of melted sulphur in an iron basin. When the combination (which is accompanied by a violent evolution of light and heat) is complete, the fused blackish mass is poured out, broken into fragments, heated until excess of sulphur has been driven off, and then sublimed in the way already described.

Some makers add to the crude sulphide, previous to sublimation, 1 per cent. of antimony sulphide, with the object of improving the colour; the product is afterwards ground, digested with liver of sulphur, and then washed with hydrochloric acid.

There are numberless processes for preparing vermilion by the wet way. One of the best of these consists in grinding, in the presence of water, 100 parts of mercury with 38 parts of flowers of sulphur until these elements have united. The black product is then triturated at 45° C. for many hours with a solution of 25 parts of caustic potash in 150 parts of water. When the product has attained its maximum of redness and beauty, it is thrown into water, and thoroughly washed by decantation. In a second process mercury, sulphur, and potassium pentasulphide are boiled together for three or four hours, and then the mixture is kept at a temperature of 50° C. for several days. Vermilion may also be prepared from the black sulphide obtained by precipitating a mercuric salt with a soluble sulphide, from 'white precipitate,' and from metallic mercury itself, by warming any one of these substances with a solution of an alkaline pentasulphide, and then purifying the product by means of a potash-solution heated to 45° C. It has also been found that vermilion is produced when a mixture of mercurous chloride (calomel) and zinc sulphate is heated to 45° - 50° C. with an excess of a solution of sodium thiosulphate.

Except where carmine or realgar (red sulphide of arsenic) is present, a very simple test suffices to ascertain whether vermilion be pure or not. A small pinch should be heated over a spirit-lamp on a fragment of hard porcelain; no appreciable residue will be found, unless red-lead, red iron oxide, brickdust, or other non-volatile adulterants be present. Carmine, which is sometimes added to scarlet vermilions to approximate their hue to that of the crimson varieties such as the Chinese, may be detected by laying a pinch of the powdered pigment on a small pad of white blotting-paper, and moistening the substance with a few drops of strong ammonia-water; a crimson stain will appear on the paper if carmine or crimson-lake be present. The colour of a good vermilion is not changed by moistening it with nitric acid. The accidental impurities which impair the hue of vermilion are free sulphur, and compounds of iron and lead; that prepared in the wet way often retains alkaline salts, owing to imperfect washing. A spurious vermilion, called anti-vermilion or antimony vermilion, is made by warming antimonious chloride with sodium thiosulphate solution.