Liangzhu Jade Bi
Thousands of jade bi, too large to be worn as jewelry, have been unearthed in elite burial sites associated with the Liangzhu culture. Variations are apparent in the size of the disks, the quality of the stone used, the level of workmanship, and the finish of the bi, yet their meaning, purpose, and ritual significance remain unknown. A century ago Charles Lang Freer acquired all of these bi largely for their aesthetic appeal at a time when very little was known of the Liangzhu culture.
Usually fashioned from even-grained dark nephrite, the most exceptional examples of bi are perfectly circular in circumference. On some, traces of sawing and grinding have been completely polished away, and the smooth surfaces are buffed to a lustrous shine. In many cases, however, the flawed stone is irregular in shape, and the disk still retains intriguing evidence of its manufacture.
Working jade is an extremely laborious process that involves both slicing and removing unwanted stone with powdered abrasive minerals, such as quartz, garnet, or corundum. Slabs were cut from boulders of jade probably found in river beds. The back-and-forth movement of flexible string or strap saws typically left traces of shallow concave cut marks. A rigid stone saw might have shaped the outer edges with a series of straight cuts. Hollow tubular bits, aided by mineral abrasives and water, could have been used to drill the central hole from both sides of the disk to avoid breakage. A tiny projecting ridge inside the hole remains if the drill bits were improperly aligned. To finish the bi, the outer edge might have been turned on a lathe. Lastly, the surface was polished with fine abrasives to create a high sheen.