Etching of quartz crystal spheres

Natural quartz crystal spheres were etched in various etchants at room temperature and at 80°C. Ten 12-mm-diameter polished natural quartz spheres were placed into each of several etchants, including 40% HF:60% NH₄F, saturated NH₄F-HF and lattice etch, at each of two nominal temperatures: 20°C and 80°C. The resulting quartz pieces were scanning electron micrographed normal to the resulting major plane and at right angles to the plane for the purpose of illustrating the anisotropy of the etch rate of quartz as a function of etchant and etchant temperature. The micrographs are presented and evaluated. All the etchants exhibit distinctly different figures at room temperature versus 80°C. This is consistent with earlier reports that crystal blanks etched at room temperature are generally "smoother" (i.e., different) than similar blanks etched in the same etchant at elevated temperatures