While high-fired white wares represent the ceramic achievements of northern China, green-glazed stonewares were the premier products of the south during the Tang period. The best – ceramics from the Yue kilns in Zhejiang province – were likened to jade. Lu Yu, the Tang tea connoisseur, rated Yue tea bowls most highly in his Chajing (The Classic of Tea). Their lustrous glaze was thought to enhance the colour of tea. Many were left plain but some sported incised decorations.