Chemical experiments have shown that in one kind of Persian paste there is a large preponderance of silex, that when fired for a certain time the result is a faience, and that a continued exposure to the kiln reduces it to a partially translucent body resembling porcelain. Some of the tiles show silica ranging about ninety per cent., and the remaining fraction consisting of alumina and iron, lime, magnesia, and potash. By comparison with the porcelain standard adopted in the table (Book I., Chapter iii.), it will be seen that this paste differs in the greater proportion of silica and in the presence of iron. It differs from earthen-ware, on the other hand, by its containing magnesia and potash. The faience of Persia must, therefore, be treated with extreme caution; and the authorities must be consulted with care, since what one calls pottery, another treats of as soft porcelain. Of that coming most nearly to what we understand by the word “faience”--that is, a perfectly opaque ware--some of the specimens are glazed, and others are covered with only a thin lustre or varnish. Very fine examples are found in the wall-tiles taken from the different mosques. The same style of ornament was applied to these and to vases, and its general character has already been designated. Arabesques and flowers--some imitations of the natural and others altogether conventional--are profusely spread upon both, with a boundless wealth of rich color. The forms assumed by the various vessels differ very widely from each other. Cups, open dishes with rims of varying breadth, and a number of water-vessels illustrate certain manners of the Persians. The color and ornamentation are distinctive. The favorite ground colors were the blues of copper and cobalt, and these alternate with red, and yellow tinged with red. The ornamentation is very often white. The Mosque of Sultaneah has already been described (see page 39). In others the colors are reversed, _i. e._, white is used for the ground and blue for the decoration. At times we see the Persian love of the chase triumphing over the Mohammedan prohibition of the employment of animal figures, by the introduction of hares or gazelles, generally upon grounds of light shades of green and blue. Some of the most remarkable plaques belong to the same period, and in both the earlier and later examples the coloring is exceedingly rich and effective. What the latter lose in simplicity they gain in brilliancy. Some pieces, apparently of great age, have a close resemblance to the céladon of China. The vases _a reflet métallique_ are either blue, or white with yellow ornamentation. The art of applying the lustre seems to have disappeared about the middle of the seventeenth century. The tiles of this kind date mostly from the time of the Mogul Dynasty. The larger plaques measure sometimes six feet by eight feet; the smaller tiles without inscriptions are star and cross shaped fitted together in a mosaic. PORCELAIN.