The oldest Chinese pottery is very hard, opaque, closely akin to stone-ware, and covered with a partially translucent enamel. The latter called Céladon, and made by mixing the colors with the glaze, varies from the old, and now very rare, sea-green to a brown-gray. The term _céladon_ was originally restricted to the sea-green variety, but was ultimately applied to all wares, of whatever color, made in the same manner. The most ancient specimens are of the coarse body above referred to. Occasionally they are decorated with incisions in the paste under the glaze, or with studs and other reliefs, or with flowered designs (_céladon fleuri_), and are called by the Chinese _Tchoui_. There is also a céladon of a deeper green than that last referred to, which, with that of the gray varieties, is very often covered with an inextricable net-work of cracks. This is the kind known as crackle. The process which the Chinese succeeded in bringing to the most exact precision in regard to the size of the cracks is not thoroughly understood. Several theories have been advanced to explain it. Examination shows that the paste or body of the ware and the glaze differed in consistency, the one being more or less expansive than the other. To perform the operation successfully, the vessel is while hot, plunged into cold water, or brought suddenly into contact with cold air, when the glaze is at once broken up into the much admired net-work of minute fissures. From this it would appear that the desired effect is caused by the shrinkage of the glaze on being suddenly exposed to cold. Another explanation is that there are two layers of paste of different composition, and that the cracks appear in the outer one. When the piece is glazed, the cracks are covered over, and the surface made perfectly smooth, unless the cracks are very coarse and large, in which case they are perceptible to the touch. Through the cracks the fused paste or inner core appeared, and made them more distinctly visible; or, to reach the same effect, ochre, ink, or other coloring material was rubbed into the cracks. To produce them with the absolute precision to which the Chinese attained, they must have thoroughly studied the composition of the paste and glaze employed, as we frequently find different kinds of crackle on the same vase.