It is too early yet to attempt seriously the classification of the T´ang wares under their respective factories. Before this is possible the meagre allusions in Chinese literature must be supplemented by far fuller information. At present our knowledge of the T´ang factories is chiefly drawn from casual references in Chinese poetry and in the Chinese Classic on Tea, the _Ch´a Ching_, written by Lu Yü in the middle of the eighth century. From this we gather that the Yüeh Chou[60] kilns enjoyed a high reputation. An early allusion to this factory in reference to the "bowls of Eastern Ou" in the Chin dynasty has already been recorded.[61] The author of the Tea Classic tells us that among tea-drinkers the Yüeh bowls were considered the best, though there were some who ranked those of Hsing Chou[62] above them. Lu Yü, however, thought the judgment of the latter connoisseurs was wrong, because the Hsing Chou bowls resembled silver while the Yüeh bowls were like jade, because the Hsing bowls were like snow, the Yüeh like ice, and because the Hsing ware, being white, made the tea appear red, while the Yüeh ware, being green (_ch´ing_), imparted a green (_lü_) tint to the tea. The T´ang poet, Lu Kuei-mêng, further tells us that the Yüeh bowls "despoiled the thousand peaks of their blue green[63] colour." Yüeh Chou is the modern Shao-hsing Fu in the province of Chêkiang. It was celebrated in the tenth century for a special ware made exclusively for the princes of Wu and Yüeh, of the Ch´ien family, who reigned at Hung Chou from 907 to 976. This was the _pi sê_ or "secret colour" ware which was made at Yüeh Chou until the Southern Sung period (1127-1279), when the manufacture was removed to Yü-yao.[64] The _pi sê_[65] ware has caused endless mystification among writers on Chinese porcelain. The name--which means literally "secret colour"--has been taken by some to imply that the colour was produced by a secret process (the most natural but not the generally accepted meaning), and by others that it was a forbidden colour, i.e. only permitted to be used by the princely patrons of the house of Ch´ien.[66] The author of the _Ching-tê Chen t´ao lu_[67] states that "it resembled the Yüeh ware in form, but surpassed it in purity and brilliance." This is, however, only the opinion of a nineteenth-century writer who does not claim to have seen a specimen of either. A tenth-century writer[68] makes use of the vague expression, "the secret colour preserves the note of the green (_ch´ing_) ware (_tz´ŭ_)," which apparently means that the secret-colour glaze did not rob the ware of the musical quality of usual _ch´ing_ ware, implying a difference of some kind between the _pi sê_ and the _ch´ing_ glaze.