A bi is a ring of jade with a hole at the centre; classical texts sort its names by the ratio of ring to hole. From the Warring States onward most were worn or displayed rather than ritual, and the cutting and polishing differ from the earlier objects.
Qing archaisms make up the bulk of the market: they copy Qing taste, not the original object — rounder grain patterns, neater edges, a glassy polish. Dating means reading the tooling, the surface and the wear inside the hole.
