Changes in orientation of etch pits produced on the cubic faces of diamond

Abstract
Cube faces of synthetic and natural diamonds have been etched in KNO3 in the temperature range 500° to 800°C Some of the square pits change orientation at 600°c, their sides lying along instead of . The re-orientation is inhibited by agitation of the crystals during etching. Two-beam interferograms show that only the deeper, larger pits undergo such re-orientation. It is conjectured that this occurs at sites of rapid local etching, and is associated with accumulation of reaction by-products.