"Song dynasty diancha really values the purity, or whiteness, of the tea foam," Zhu says. The foam is also much thicker than that of matcha, which only requires brief whisking.

The coins in England were likely minted during the reign of Emperor Shenzong of Song, who ruled from 1067 to 1085 A.D. and were in circulation after the dynasty ended in the 1120s, per Green’s ...