Chinese used diamonds and sapphires to polish ceremonial burial axes as early as 6,000 years ago. The axes, which are made from corundum (or ruby in its red form and sapphire in other colors), were polished to a mirror finish.
|Diamond-polished corundum axe from the Neolithic Liangzhu culture of ancient China, ca. 2500 B.C. Photo by Peter J. Lu|