We may expect, then, to find the influence of these more precocious arts on the early fictile ware of China, and indeed we see the quaint decoration and the not too beautiful outlines of the early hieratic bronzes repeated on the rare specimens that survive from the dynasty that after a period of unrest followed that of Tang. This was the Sung dynasty, which lasted till the time of the Mongol invasion in the thirteenth century.[27] It is difficult for a European to appreciate the charm, or rather superlative excellence, that is found by a Chinaman in a fine specimen of jade. It is, however, a substance that is closely linked with his philosophy, his religion, and above all with his all-important ceremonial. No wonder, then, if from an early time he strove, with the pastes and glazes at his command, to imitate such a material. And numberless references in contemporary writers, as well as the evidence of many of the oldest pieces of porcelain surviving, show that this was the case. We may safely say that in these early specimens the thick glaze, of tints varying from a true celadon to a more pronounced blue or green, was admired in proportion to its resemblance to jade. As for the porcelain itself, all that was looked for in the paste was that it should be hard, and that the vessel when struck should give out a bell-like sound--‘a plaintive note like a cup of jade,’ as one early Chinese writer says of a porcelain cup in his collection. The Chinese in these times possessed also elaborately carved vessels of rock crystal and of various kinds of chalcedony, and these also it was attempted to imitate with the early glazes. Glass, too, as a material for small objects, was probably known; it seems, however, to have been somewhat of a rarity. It is mentioned by writers of the Tang period in connection with these early wares, and indeed it is possible that there may be some confusion in the literature of the time (or rather perhaps in our interpretation of the language used) between the two materials--the thickly glazed porcelain and the more or less opaque glass. After these preliminary remarks we shall be in a better position to interpret the somewhat involved and contradictory allusions to our subject found in Chinese books.