Ancient Chinese jades frequently have white chalky areas which invade the otherwise firm polished surface. It appears to be restricted to tomb jades of the Shang to Han dynasties. The alteration appears to be due to leaching along grain boundaries by ammoniacal solutions of high pH produced during decay of the corpses with which the jades were buried. X-ray diffraction and scanning electron microscopy have yielded information leading to this conclusion. Artificial alteration tests in the laboratory produced identical effects to those seen on ancient jades. -- AATA