It's probably porcelain. The production technology of porcelain in Song Dynasty reached a high level. Porcelain kilns are all over the country, with five famous kilns, namely Ding Yao (Quyang, Hebei), Ruyao (Baofeng, Henan), Geyao (Longquan, Zhejiang), Guanyao (Kaifeng, Henan) and Junyao (Yuzhou, Henan). The porcelain produced is quite famous. Jingdezhen is also known as the porcelain capital.