The most popular tumblers have a barrel that is loaded with rocks, water, and abrasive grit. The abrasive grit is a granular material similar to the grains glued onto sandpaper. The grit is often labeled “coarse,” “medium,” and “fine,” similar to the different grades of sandpaper.

The barrel containing rocks, grit, and water is placed on a motorized machine that rotates the barrel to tumble the rocks that are inside. As the rocks tumble, they grind against one another with particles of the abrasive grit caught between them. This action wears sharp edges off of the rocks and smoothes their surfaces. Tumblers that operate this way are known as “rotary tumblers.”

The rocks are typically tumbled for one or two weeks in coarse grit, one week in medium grit, and one week in fine grit, with a thorough cleaning of the rocks and the barrel between each grit size. Then the rocks are tumbled for one final week with water and a rock polish. After following this procedure, the rocks are usually transformed into brightly polished stones.