gems, jade, China, Chinese jade carving, Chinese lapidary arts, archaic jades, nephrite

The ancient Chinese regarded yu, which we commonly call jade or nephrite, as the noblest material suitable for the expression of their religious symbols. From its extreme hardness they inferred its invulnerability and, consequently, its permanence. However great this hardness may be, jade is not immune to attack by groundwater; indeed, many objects are found that have undergone, wholly or in part, a transformation into magnesium silicate (talc) and calcite under the influence of the excess carbonic acid in the waters with which they remained in contact for centuries. Even more frequently, they have been subjected to more or less deep impregnation by ferric oxide, resulting in overall or partial tones ranging from yellow ochre to dark brown. These colors are highly prized by collectors, who rightly regard them as evidence of relative antiquity. The archaeology of jade, still in its infancy, applies only to the northern provinces of China, drained by the Yellow River, which constituted the empire of the Zhou dynasty (1122–256 BC) and continued to play a primary role in the expanded empire of the Han dynasty (206 BC–AD 220). The provinces of Shaanxi and Shanxi, with Xi’an, have thus far been the principal centers of discovery.