Excellent on sea shells and small beach stones
After spending half an hour on a thick sea shell (along with others) and still breaking them, I tried the diamond coated drills. They have worked perfectly using a hand held dremel with little heat generated (using the BR180 Cutting Lubricant). Through repeated cycles of providing pressure of the bit on the shell and easing up, it draws the fragments up and out. I add some lubricant to the divot created after the initial drilling to get the lubricant to stay. I also make sure that wherever I'm applying pressure on the shell with the bit, the back side of it is resting directly against a firm surface. On curved surfaces, I push the curved part over a corner of a piece of wood underneath so as to not stress the surrounding area of the shell and crack it). I've had very good luck with these bits.
Reviewed by: Benny Glandon from Largo, Florida.