214. VIOLET CARMINE
is a brilliant bluish purple of much richness, employed in draperies and the like. It is prepared by precipitating an alcoholic extract of the root of the Anchusa tinctoria, commonly known as alkanet, a plant growing in the Levant, and some other warm countries. It was used by the ancients as a dye, or as a groundwork to those stuffs which were to be dyed purplish-red: the ladies in ancient times also employed it as a paint. Its colouring matter or anchusin has the character of a resin, and is dark-red, softened by heat, insoluble in water, soluble in alcohol and alkalis, and freely so in ether, fats, and volatile oils, to all of which it imparts a brilliant red hue. To obtain anchusin, all the soluble matters are first abstracted from the bruised root by water: it is then digested in a solution of carbonate of potash, from which it may be readily precipitated by an acid. Its alcoholic solution yields with different reagents crimson, flesh-coloured, blue, and violet precipitates, none of which, however, can be classed as durable. The variety under notice, violet carmine, resembles the other colours afforded by alkanet in not being able to withstand the action of light. On continued exposure, it loses its beauty and brightness, together with much of its colour, and, like Indian purple, assumes an inky blackness. Hence it is unsuited to permanently pure effects, and should only be used in body.
215. Archil Purple.
Archil may be regarded as the English, cudbear as the Scotch, and litmus as the Dutch name for one and the same substance, extracted from several species of lichens by various processes. These lichens, which are principally collected on rocks adjacent to the sea, are cleaned and ground into a pulp with water, treated from time to time with ammoniacal liquor, and exposed with frequent agitation to the action of the atmosphere. Peculiar principles existing in the lichens are, by the joint instrumentality of the air, water, and ammonia, so changed as to generate colouring matter, which, when perfect, is expressed. Soluble in water and alcohol, this colouring principle yields by precipitation with chloride of calcium a compound known as 'Solid French Purple', a pigment more stable than the archil colours generally, but all too fugitive for the palette.
216. Bismuth Purple.
A purple powder is capable of being produced from bismuth by passing chlorine gas through the hydrated oxide suspended in a saturated solution of potash. As soon as the oxide becomes brown-red, the mixture is boiled and the liquid decanted off at once, the residue being immediately washed first with alcohol and then with water. On the whole, the result is not, for an artistic pigment, worth the trouble involved in the preparation.
217. Burnt Madder
is obtained by carefully charring madder carmine until it becomes of the hue required. Bearing the same relation to madder carmine as burnt carmine to the carmine of cochineal, burnt madder is a permanent and perfectly unexceptionable pigment. By reason, probably, of its great price, it is not mentioned in trade catalogues, and must be held as commercially unknown.