344 Sloan's Architectural Review and Builders Journal. p T ov., for its employment, in the discovery and application of the fact, that many heavy metallic oxides will combine with silicic acid ; and that the salts, then produced, can be united, in all propor- tions, with the ordinary colorless glass, giving rise to a variety of shades and colors and producing the ordinary -colored glasses, the glass-pastes, for jewelers, and the pigments for bona fide Glass-Painting. In the ordinary colored glasses, the yellow is produced by antimony, or by a mixture of antimony, minium and oxide of iron ; but the intense red is imparted by the small amount of the sub-oxide of copper, as recently dis- covered and pressed into service. It was to this, that the glass-paste, found at the Yilla of Tiberias, on the Island of Capri, owed its brilliant color, so that its use must have been known at a very early period. The art was, for a long- time, a lost one — or, at least, if pre- served in books and manuscripts, en- tirely unpractised — and it is only within a few years, that it has been rediscovered and revived. An equally brilliant red is produced by gold. Greens are ob- tained by protoxide of iron, fts in the ordinary bottle glass, and oxide of cop- per. A perfect imitation of the emerald is obtained by a mixture of the oxides of copper and chromium, whilst the blue glass is colored by oxide of cobalt. It may strike the reader as somewhat incongruous, that colored glass should be mentioned as of recent origin ; and as having been one of the fruits of modern chemical research, when it is known to have existed, in the windows of churches, as early as the 3d century ; and when the most beautiful specimen known, the celebrated Portland Vase, was found and removed from the tomb of Alexander Severus, who died, A. D. 235. From the total unacquaintance of the ancients with a knowledge of the chemistry of the heavy metals, there is but the one conclusion to draw, that such productions were the result of chance ; and that the same results could not be indefinitely repeated, as at the present time. Knox made the observa- tion, that all metals, with the exception of platinum, are dissolved, as such, by- melting glass ; and that they impart color to it, if the heat is continued for a length of time, sufficient to bring about combination. Chance observa- tions of this kind have unquestionably been made in the glass-houses. Among the most interesting of the glasses are the white and the enamels, which are produced by oxide of tin, antimonious oxide, chloride of silver, and phosphate of lime or bone ashes — the last producing a beautiful opalescent or milky white. In our own city, the " American Hot Cast Porcelain Co." are now manufac- turing a material, resembling in appear- • ance, the ordinary French China; and susceptible, not only of all the uses to which that substance is applied ; but, also, of all the manipulations of the ordinary glasses. The translucencj', or, rather, semi-translucency, of this substance is due inanity to oxide of zinc, cf which it contains, according to a recent analysis, about eight per cent. From the white opaque glasses, the transition is natural and easy into the highest division of the Ceramic Art, that of Porcelain Manufacture. The popular title of this substance denotes the origin of the art, as do the names of the substances emplo3 T ed in its produc- tion. From that mysterious and re- markable people, the Chinese, we get the words Kaolin and Petuntse, the two ingredients entering into the composi- tion of the true Porcelain, the first being, the infusible ingredient, or clay, the second, the fusible feldspar, or petro- silex.* Our word, itself, is said to be
- "Kao-ling is the name of a mountain situated to the
east of the King-te-chin. The Pe-tun (white paste) of pulverized petro-silex, when formed into bricks (tse), is called Pe-tun-tse, i. e, bricks of white paste Bricks are also formed of colored paste, hoang-tun-tse, i. e., bricks of yellow paste, etc." — Marryat, loc. vit., page 179.
