Note: In the Tang dynasty, fresh tea leaves were first steamed, then ground in a special mortar, later compressed into cakes and strung with reed or bamboo to dry. To brew the tea, the cake broken and ground into a fine powder, sifted, and boiled. A full set of gilt-silver teawares excavated from Famen Temple, Fufeng County, Shaanxi in 1987, provided solid material evidence to how imperial tea ceremonies were conducted during the Tang dynasty.

Whilst mortars made of gold and silver were reserved for royal use, ceramic mortars of similar nature were known to have produced in various kilns. Compare a closely related white-glazed rectangular mortar of similar form in the collection of China National Tea Museum in Zhejiang, Hangzhou is illustrated in their website.

A white-glazed rectangular mortar, in the collection of China National Tea Museum in Zhejiang, Hangzhou.

Sotheby's. Echoes of Fragrance – Evolution of Tea Culture from the Tang to the Qing Dynasties, Hong Kong, 16 December 2021