I'm using 500 Rpm. I have been told by a man that was friends with, "The Geode-Kid". He was a very intelligent man who actually developed the main theory on the formation of thundereggs. I was told to use it dry and to then use a canvas pad stretched over a aluminum 8" disc spinning at 500rpm. The polish they achieved was absolutely astounding, no scratches visible at all. I need a lot of help and advice in order to learn how to polish these to the best possible. If you don't know who the Geode kid is, look it up, it is a very interesting story that took place in the small but amazing town of Deming, New Mexico. Please send any advice possible. Thank you!