Az′ure. Syn. Azure Blue. A name frequently given to smalts. That of the oil-painter is ultramarine; that of the ancients is noticed below. See Ultramarine, &c.
Blue, Barth’s. See Indigo, Sulphate of.
Blue, Berlin. Prussian blue.
Blue, Bice. Native blue carbonate of copper, prepared by grinding and elutriation. That of the shops is generally a factitious compound made from smalts.
Blue, Carmine. See Carmine and Indigo, Sulphate of.
Blue, Char′coal. Carbonised vine-stalks are triturated with an equal weight of salt of tartar or pearlash, the mixture put into a crucible, and heated over the fire until it ceases to swell, the mass being kept well stirred all the time; when cold, it is dissolved in water, and the excess of alkali saturated with dilute sulphuric acid. The liquid becomes blue, and a dark precipitate falls down, which turns of a brilliant blue colour when dried and cautiously heated.
Blue, Chi′na. Syn. Roy′al Smalts. The crude oxide of cobalt, or zaffre, is ground with an equal weight of potash, and about eight times its weight of felspar, the mixture submitted to fusion in a crucible, and when cold reduced to an impalpable powder. Used to paint pottery, and as a blue pigment.
Blue, Co′balt. Syn. Cobalt′ic Az′ure. This is commonly prepared by one or other of the following formulæ:—
1. Zaffre, 1 lb., is dissolved in nitric acid (diluted with an equal weight of water), 3⁄4 lb., by digestion for some hours; the solution is evaporated nearly to dryness, and the residuum redissolved in warm water; to this solution, after filtration, a solution of phosphate of soda is added as long as a precipitate forms; this last is collected on a filter, washed with cold water, and mixed, whilst still moist, with 8 times its weight of fresh-precipitated hydrate of alumina; the paste is then dried, and exposed to a cherry-red heat in a crucible, after which the mass is cooled and reduced to a very fine powder.
2. A solution of nitrate of cobalt is precipitated with ammonia-alum, and the precipitate washed, dried, and exposed to a cherry-red heat, as before. The products of the above formulæ are very beautiful and permanent. See Cobalto-ultramarine.