Rock tumbling and stone polishing is a popular hobby. The most important ingredient to achieving a great finish is time. Polishing is typically a 4-step process involving progressively finer and finer abrasives. Each step is done with a clean barrel, fresh water and a virgin abrasive. The Creetown Gem Rock Museum (in the UK) has a good outline for polishing stones.
The first three steps require a coarse grit (80 mesh) followed by a medium abrasive (220 mesh) and finally a fine grit (400 mesh). Aluminum Oxide or Silicon Carbide are the preferred media due to their durability and hardness.
The fourth step demands a very fine, hard media that will maintain it’s ‘cutting’ ability for the entire cycle time. Cerium or tin oxide are the abrasives of choice as they will maintain their sharp edges as they break down over time. Sawdust can be added to this step to ease the impact and eliminate chipping of the stones.
Hobby size barrel tumblers will generally have capacities of just a few pounds of stones. Tumbling times for each step is about 1 week. Larger, industrial-grade tumblers such as the MT Series Barrel Tumblers will allow for more weight to be tumbled at one time. This often leads to reduced cycle times and higher production rates. Regardless of the equipment, patience is the key to beautifully polished rocks and stones.