The sea-greens (_céladons_) are among the rarest Chinese colors, and some pieces are thought to be among the oldest--dating back possibly one thousand years. The violets and crimsons are also rare and beautiful; they are almost always applied to vases and bottles; and are often flamed, splashed, or clouded. The imperial yellow, some pieces of which are in the Green Vaults at Dresden, was never sold; it was made only for the royal family of Peking. I have not seen it, but it is described as a very clear and beautiful citron-color. Marryat mentions two pieces in Mr. Beckford's collection as having been sold for their weight in gold; they would now sell for ten times that. The small incense-pot (Fig. 111) is from Mr. Avery's collection. It is a very pure lemon-yellow, and is quaint in form and peculiar in every way. Nothing can be better here than the condensed information prepared for his catalogue by Mr. A. W. Franks. It is as follows: "The tints are very numerous; we find, for instance, sea-green or _céladon_, yellow, red, blue, purple, brown, black, and several variegated hues. These glazes owe their color to various metallic oxides, of which an account may be found in the 'History of King-te-chin,' book vi., section xi. The exact tint must be in some measure due to the amount of firing which the vase has undergone, and the mottlings and other variations of color which they present must have been to a certain extent accidental. "Among these simple colors the first place must be assigned to the bluish or sea-green tint, termed by the French _céladon_. It is probably of considerable antiquity; and it is remarkable that the earliest specimen of porcelain that can now be referred to as having been brought to England before the Reformation--the cup of Archbishop Warham, at New College, Oxford--is of this kind. By the Persians and Turks it is termed _mertebani_, and it is much valued by them as a detector of poisonous food. Specimens of this porcelain were sent to Lorenzo de' Medici, in 1487, by the Sultan of Egypt. It owes its preservation, no doubt, to its great thickness. The surface is sometimes covered with impressed or engraved patterns filled in with the glaze. "Yellow glazed porcelain is much valued by collectors, owing to the supposed scarcity of specimens of this color, it being the imperial color of the reigning dynasty. Many of them, however, bear dates of the Ming dynasty, when the imperial color was green, and can therefore have no relation to the emperor. "The red glaze is of considerable antiquity; some of the vases made under the Sung dynasty at Tsing-cheou are mentioned as resembling chiseled red jade. One tint, the _sang de boeuf_ of French collectors, is much valued in China. Occasionally portions of red glazed vases appear purple, owing probably to a different chemical condition of the coloring-matter in those parts.