All, I stayed out of the initial discussion on polishing a hole in a
stone. All the basics were covered. I would like to add that there
are a lot of industrial diamond compounds available through dental
supply stores that are really good for lapidary and metal. In
diamond polishing the carrier in which the diamond is mixed, the
concentration of diamond mixed in the carrier, and the medium on
which you are going to apply the compound to the stone make all the
difference. Motor speed is also important. Experimentation is
necessary to find which combination works best on which material. I
could fill a book with notes on what works and does not work for me.
You are better off experimenting your self.