I've just started some gem-cutting as a hobby and am having problems polishing a few stones like Zircon. I've heard you're supposed to use a plastic lap but this does not seem to work well. Does anybody have a list on what laps work best for what gemstones?
Throw away any idea of using a plastic lap. They work O.K., but they merely extend your time of frustration in obtaining a really good polish, as they only work for some things. Go to any of the internet lapidary suppliers and get yourself a couple of BATT laps. These are a hardened tin lap that works really well when they are properly embedded with diamond compound. You need at least two of them in order to get the appropriate pre-polish. Here's my cutting sequence for cutting and polishing everything:
1. Rough cut to form with 600 grit.
2. Final form with 1200 or 3000 (on Batt or ceramic, depending on the material being cut)
3. Prepolish with 8k or 14K on batt or ceramic, (this step is REALLY critical).
4. Final polish with 100K on Batt
If you go to Yahoo groups and sign up for the USFG Faceters Digest you will get more information than you can digest in a year. Well worth your time, but if you want to cut your learning curve short, the above methods work well. Remember that zircon is really brittle and that it can be severely damaged, microscopically, by the use of a lap that is too coarse, (NEVER use anything coarser than 360 and that's pushing it). This means that you won't be able to see the subsurface damage until you start to polish and then the "suction" of the polish lap will suck pieces right out of the surface and facet junctions and ROLL them right across your almost polished facet. This can cause problems that take years to figure out, so I've just saved you a couple of years of pain and frustration. If you have any particular questions, send me an e-mail or ask on the Faceters Digest, (be prepared to read a lot of opinions !).
I would also suggest a treated ceramic lap like "Pol a Laps" made by Glenn Vargas if you can get your hands on them. I've recall having success getting a flat polish with zircon using that type of lap although it has been a little while. I don't' get zircon rough all that often. It is true the better your prepolish is, the more successful you will be in the final polish.
My last stone cut was a zircon- raytech 1200 to BATT 3000 to diamond 50K on a lightning lap with a layer of trewax polish and water to rid the slurry. But the table was a problem and a friend tried a corian lap with voodoo polish- worked like a charm in under two minutes.