Blue is one of the primitive colours. In limning, miniature, etc, the painters use ultra-marine, blue ashes, and smalt. In oil and miniature they use indigo, blue bice, blue verditer, lapis Armenius, smalt, also a counterfeit ultramarine. Dyers' Blue is one of their simple or mother colours, used in the composition of others. It is given chiefly with woad and indigo.
Indigo is a deep blue, brought from the West Indies. It is drawn from the leaves of a plant which the Spaniards call anil, and we nil, Indian wood, and indigo. When the plant has arrived at a certain height, and its leaves are in a good condition, they are cut down, thrown into a vat, and covered with water; at the top swims a scum, with all the different colours of the rainbow. Then the water is let off into another vessel, -where it is agitated with five or six long poles, fitted together for that purpose. This is continued till the water appears of a deep green, and till the grain, as it is called, forms itself, which is discovered by taking a little of it into another vessel, and spitting in it, when, if a bluish dreg be perceived subsiding, the violent agitation is discontinued. The matter then precipitates to the bottom of the vessel, after which the water is poured off. It is then put into little linen hags to drain, and when dry, it is cut into slices and hardened in the sun. There are several kinds of indigo. That is thought to be the best, which is in flat pieces, of a moderate thickness, pretty hard, clean, light enough to swim in water, inflammable, of a fine blue colour, marked a little on the side with silver streaks, and appearing reddish when rubbed on the nail. Indigo is used among painters, who grind it and mix it with white to make a blue colour, for without that mixture it would paint blackish. It is mixed with yellow to make a green colour. It is also used in dyeing, and may be considered as the best basis of all black, blue, and green colours. With indigo, laundresses give a bluish cast to their linen.
Smalt. A metallic oxide, prepared, purified, and sold, sometimes in the state of a blue powder, and sometimes in cakes; chiefly used along with starch to give linens a finer and cleaner cast; and best known by the name of stone or powder-blue.
Blue Verditer, is a bright blue. It works easy with water. It is somewhat inclining to a green, and it is the blue which is most of all mixed with yellow berries. Verditer is the precipitate obtained from nitrates of copper by lime, powdered with the addition of from 5 to 10 parts of lime in 100.
Next to ultramarine, Blue Bice (a preparation of lapis Armenius) is the most excellent, and is often made to serve instead of it. It works much better than smalt.
Ultramarine. A beautiful blue colour, used by the painters, prepared from lapis lazuli. This is a sort of precious stone, called also azure stone. It is found in mines of gold, silver, and copper, as also in pits of marble, which last is that generally in use. It is composed of silex, sulphate of lime, blue fluor spar, and iron. The Armenian stone bears a near resemblance to lapis luzuli. It is a blue friable copper ore.