1. Deciding on the correct size for your rock tumbler is pretty simple and follows what common sense would tell you. For stones smaller than 1 in. in diameter, go with a model as small as 3 lbs. Six- and 12-lb. barrels can handle stones of up to 2.5 inches.
2. Tumblers that accommodate approximately 1.5 lbs. should be reserved for small, coin-sized stones. These size restrictions are important because, for a good polish, it's necessary to keep the chamber about half-full.
3. If you want to eliminate the risk of jeopardizing the polish in the last stage, or if you want to expedite the process, a second tumbling barrel is a great choice for getting this done.
4. Of course, purchasing a two-barrel rock tumbler is a bit more expensive. This is naturally more economical than buying a second machine, and you can process more stones at a quicker pace.
5. The question of vibrating vs. rotary is one you're bound to face. Essentially, both types produce a good polish, but the latter is easier to operate and makes smoother, more rounded surfaces.
6. The agitating mechanism helps keep the shape of the stone constant, whereas the alternative technique rounds out edges and angles. Therefore, if you go to a lot of trouble to shape your stones prior to polishing, a vibrating model is best.
7. An additional feature of the vibrating tumbler is that its cycle finishes in 7-10 days, compared to the month to 45 days needed by a rotary unit.
8. The advantages of rotating units include ease of use and economy. They can, at times, cost half as much as their vibrating counterparts.
9. Rotary machines, because of their increased kinetic activity and need for more polish, are not recommended for fragile rocks. They are also occasionally prone to leaks.
10. Plenty of books are available about rock polishing and tumbling for hobbyists and professional jewelers. There are also gem clubs, operated by "rock hounds", who can help you get started and offer custom advice.