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Another hypothesis for the polish on the Stone Age corundum ax head is that the Stone Age people never had absolutely pure corundum, which indeed would have required diamond to polish. It is possible that these people used one grade of corundum to make the ax head and a slightly harder grade to polish it. The difference in hardness would serve the purpose.

James E. Burkart
Bethesda, Md.

Researcher Peter J. Lu says that his group tried pure corundum, the highest-grade possible, as well as quartz and diamond, to polish the ax. Only the diamond produced the smoothness of the original axe heads. —A. Goho The article was very interesting. In looking at the photo, however, the first question that came to my mind was, How did these Stone Age craftsmen create the large round hole through the ax?

Joe Sardina
Fairport, N.Y.