How Rock Tumblers Work

Coarse Grinding

Rock tumblers simulate the natural process of erosion, but on an accelerated time line. The first stage of rock tumbling is the "coarse grind," where a coarse rock powder, called pumice, and water are added to a barrel of a rock tumbler containing rough-cut rocks. The coarse grind breaks off sharp edges and makes a more even, or smooth, rock. Some rocks are completely demolished in this process, which can take between 24 and 48 hours to complete.

Medium Grind

The next step is the introduction of a medium pumice; medium pumice is ground finer than the coarse kind. The rocks that survived the coarse grind are placed in the clean barrel with water and the medium pumice. As the rock tumbler turns, the medium pumice will smooth out the rough edges and reveal a shinier rock. This process also takes between 24 and 48 hours.

Fine Grind/Polishing

A fine pumice, or sometimes plastic beads, are used for a fine grind or polishing. In some rock tumbler sets, this process is two separate stages. Again, the mostly refined rocks are placed in the clean barrel, and water and the fine powder/beads are added. The beads and fine powder put a more refined shine on the rocks as the barrel tumbles. The result is gem-like rocks that typically have glassy finishes. This process usually takes around 24 hours to complete.

References

• How Rock Tumblers Work
• About; rock tumblers