[Favorite Tip] Pumice Wheels

Test your pumice wheels and other abrasive wheels on a piece of
glass. If they do not abrade the glass, they will not scratch most
faceted colored stones, and would be safe to use cleaning up the
prongs. Glass is around 5 BD on the Mohs scale, which is softer
than most faceted colored stones. Although these wheels will not
scratch harder you still must use caution as the wheel
may chip the facet lines of fragile stones. Brad Simon CMBJ