Fig. 466.—Stampers.
Fig. 467.—Flint mill.
Earthenware utensils are made of a coarser material,—clay and powdered flints,—from which all the gross matter has been eliminated. Flint is not difficult to break, if made hot and thrown into cold water. A stamper is then used to break the flints. They are first ground in a mill and purified like the clay, then they are mixed and beaten, while moist, into “putty,” and turned, or forced, into moulds. The handles are fixed on afterwards. The ware is baked for two days and glazed. The various colours are obtained by mixing different clays and oxides—iron or manganese. Biscuit porcelain is made by pouring a creamy mixture of porcelain earth into plaster-of-Paris moulds, and when a thin case has formed within, the liquid is poured out again. It is then dried in the mould and shrinks. The mould is taken to pieces, and the thin biscuit porcelain is left.
Fig. 468.—Felspar.
Felspars are very like the zeolites, except that the former contain no water. Felspar crystallizes in a number of different forms. We annex illustrations of specimens. This spar is found in rocks, granite, gneiss, etc. One variety is the moonstone, of a peculiar lustre. Felsite is amorphous felspar. Albite contains soda instead of potash. Labradorite is nearly a pure lime felspar, and is remarkable for its colours, like a pigeon’s breast. Spodumene is like albite, and leucite, soda-lite, etc., belong to this family.
Fig. 469.—Felspar crystal.
Lapis-Lazuli is a felspar distinguished by its blue tint. It was used for ultramarine colouring at one time, which colour can also be made chemically. Lapis-lazuli is found in Siberia and China. It is a mixture of mineral species. Hauyne is something like it. Obsidian is a sort of black glass, and occurs in various colours in vitreous masses. It is derived from the fusion of rocks, and is employed in the manufacture of boxes, etc. Pumice stone bears a resemblance in composition to the foregoing, but is porous, and so called spongy. It contains both potash and soda in some quantities. Pearlstone and pitchstone also attach themselves to this family group.