The success of the Yue kilns in northern Zhejiang province was closely linked to the strength of the Wu-Yue kingdom (907-978 C.E.). The kilns produced high-fired grey stoneware with a grey-green glaze, often with a bluish tinge. The characteristic lobed shape of the vessels and the engraved bird and flower designs derive from the silverware of the earlier Tang dynasty (618-907 C.E.). The finest Yue pieces, known as bise yao (“prohibited” or “private” colour ware) were apparently reserved for the exclusive use of the princes of the Wu-Yue and, as such, are often considered China’s first “official” ware. The kilns produced ink stones and water droppers for the writing desk and vessels for the consumption of tea. In his celebrated Cha Jing (The Classic of Tea), the eighth-century writer Lu Yu praised Yue bowls, comparing their subtle green glaze to jade.