Several Ways to Polish Sapphires
There are several ways to polish Sapphires, it really depends on what you are cutting for fun or contests.
Be sure and read my article on cutting “Simple Heart” if you are interested in seeing how I cut Sapphires.
If you are cutting for a contest type of stone, I would recommend that you use a ceramic lap. “Do I need a ceramic lap and how do I get it to work?” The ceramic lap will give you the best, flattest facets. But isn’t there always one?
A lot of people, including me have a love/hate relationship with ceramic laps and they can be both hard to get working (broken in) and to keep working. The other drawbacks, and major ones as far as I am concerned, are that they are slow, can be undependable, and heat the stone (which can cause the stone to shift on the dop), and are expensive compared to other laps.
I use Zinc or tin laps (I say laps because I use one for 8,000 pre-polish and one for 50,000 final polish), it is the old timers way to do it, but I have found that it works very well, is fast and dependable, and will not heat your stone. From a commercial cutters stand point, Zinc/Tin is the only way to go. Most pros that I know only polish to 14,000 with Zinc/Tin laps. It looks like a higher polish than that, but 14,000 is pretty much standard for commercial cutting. The Zinc lap(s) polish a nice flat facet, though not as flat as the ceramic lap. But Zinc/Tin polish much faster and easier and I do not see all that that much difference between a stone polished with Zinc (or Tin laps) and a Ceramic lap to be honest.
Polishing with Zinc and Tin Laps. First thing you need to do is score your lap(s).
I use a fairly heavy diamond concentrate that I make, I think it works better than the commercial stuff. 10 carats of powdered diamond dissolved into a small jar of Vaseline, melt the Vaseline and mix in the diamonds, stir until it cools and jells. But you can use the commercially prepared diamond spray if you want to, I do sometimes and it seems to work well. Charge your lap(s) with a fair amount of diamond compound, and work it into the lap. It will take a couple of stones for the lap(s) to really start working well.
To Polish, run the lap full speed and with a gentle touch apply the stone to the lap, keep the stone moving in a nice arc. This is a little strange at first to get used to, most other polish laps are used pretty slowly, but the diamonds really seem to work better with more speed. The stone will pre-polish 8,000, and polish 50,000 fast, so keep an eye on it and check often.