Stone polishing, or rock tumbling, is a hobby enjoyed by adults and children around the world. You will need a good quality rock tumbler and a variety of rough-cut rocks or semiprecious stones to get started. Polished stones add beauty and color to hand-crafted jewelry and other crafting projects. For the patient crafter, stone polishing can be a rewarding experience.
A tumbling machine rotates barrels that contain your stones. Plastic pellets, placed with the stones, help protect the stones from damage during the tumbling process. You will need four sieves, one for each of the three grades of grit and one for the polish. A tea strainer makes separating plastic pellets and stones easier. As rock tumbling can be messy, you need a collection of old newspapers, paper towels and rags to keep slurry under control.
A rock tumbler, owned by a serious crafter, runs nearly nonstop for years, so it is a good idea to purchase a good quality machine. The average cost of a tumbler is around $150, as of 2011. The machine itself consists of a motor and two horizontal bars that support the rotating barrels. You need four plastic tumbling barrels, one for each grade of grit and one for polish at around $30 each for a 3-lb. barrel; larger sizes are available as well. Grit is around $5 to $10 per pound, and you need coarse, medium and fine grades. Aluminum oxide polish runs about $1 per ounce. Plastic pellets are about $6 per lb.
Stones known as tumbler rough include agates, jaspers, quartz and Apache tears that range in size from 1/4 inch to 1 1/4 inches in diameter. Crafters can purchase tumbler rough for about $6 per lb., but many crafters prefer to find their own stones in nature while hiking, fishing in streams, swimming in lakes or visiting ocean beaches. In addition to stones, petrified wood, placed in a tumbler, produces shiny, wood-grained stones.
For the first cycle, the shaping phase, use 80-grit to shape the stones. The first cycle needs to tumble for five days without stopping. If satisfied with the size and shape of the stones after five days, move on to Phase 2. Empty the tumbler and clean the stones, carefully checking for grit lodged in pits and crevices. Use 220-grit for Phase 2 and 400 grit for Phase 3. Cycles two and three should tumble for four days each. Phase 4 is polishing. After washing stones a minimum of two times, place them in the polishing barrel with the polishing compound and tumble for two days. Be careful here, as a single grain of grit prevents stones from shining. After two days, check stones for results. Repeat every two days until satisfied with their appearance. Once satisfied, continue to tumble for four more days.
Tips and Alternatives
With stone polishing, patience is a virtue. In nature, it takes hundreds to thousands of years for stones to become polished gems. Although polishing stones in a tumbler is much quicker, it still takes time. Depending on the type of stone, it will take a minimum of three weeks to produce quality polished stones. Be sure to follow your tumbler’s instructions, as rushing the process will prove to be a great disappointment. If you have a small number of stones to polish for a special project, a rotary tool is an effective way to get the job done without the need of a tumbler. Use a grinding accessory to initially smooth a rough stone surface, working your way from rough to fine accessories. Finally, use a polishing wheel accessory and polishing compound to create a smooth finish on the stone.