How Rock Tumblers Polish Rocks

Rotary rock tumblers round rock in the same way a river does.  By rolling the rock over and over, the sharp edges are worn away, until a smooth surface is left.  Nature uses dirt, rock and sand as the abrasive to wear down the rock. 

Tumblers use silicon carbide grit, which is much harder than sand, and therefore much faster than nature's process.  When tumbling, we start out with a coarse grit, move to a fine grit, then proceed to a silicon sand step.  Finally, unlike nature, we end up at a polishing stage with any of a variety of commercial polishes.  A common polish is titanium dioxide, which is the same polish used in your toothpaste.  Let's look at each step more closely.

In step one, the rock, the coarse grit, and water are added to the tumbler barrel.   With the lid replaced, the barrel is allowed to turn on the base.  The rate at which the barrel turns is proportional to the size of the barrel.  Rock tumblers turn very slowly to allow the rock to "climb" the inside wall of the barrel.  As the rock reaches the top of the wall, it tumbles down the other rocks and into the slurry or mixture created by the grit and water.  The next time around, the rock will carry the slurry mixture with it onto other rocks.  Using a variety of rock sizes will improve your final result.  Small rocks have a better chance of reaching odd shaped places in larger rocks.  If too much water has been added, the slurry will be too thin and the rocks will "float" rather than cascade down.  If the barrel is too full, the rocks don't have room to cascade down.   If the barrel is not full enough, the rocks won't "climb" the wall. 

The same process occurs in steps two through four.  Each step should run for one week.

Step one rounds the rock.  Step two takes the deep scratches out of the rock.   Step three removes more fine scratches.  And step four adds a permanent gloss shine.

So now you know.  Rock tumbling is a simple process that mimics nature.  With a little care, you can easily polish your own rocks into gemstones!