Azure-Stone, or Lapis-Lazuli, is a massive mineral, of a fine azure blue colour. Lustre, glistening. Fine grained, even fracture. Scratches glass, but scarcely strikes fire with steel. Opaque, or translucent, on the very edges. Easily broken. Spec. grav. 2.85. It consists, according to Mes. Clement and Desormes, of 34 silicia, 33 alumina, 3 sulphur, 22 soda, loss 8,=100 parts. The finest specimens are brought from Persia and China. It is from these stones that the beautiful unchangeable blue pigment, ultramarine, is prepared. The stones are first made red hot, then thrown into water to cool them suddenly, which enables them to be easily pulverized. The fragments are then reduced to a very fine powder in a mortar, and intimately combined with a varnish composed of resin, bees-wax, and linseed oil. It is then of the consistence of paste, and is put into a linen cloth, and repeatedly kneaded with hot water. The first water is thrown away, the second gives a blue tint of the first quality, and the third yields one of less value.

This processis founded on the pro-perry which the colouring matter of the lapis-lazuli has of adhering less firmly to the resinous cement, than the other matter with which it is combined