How to Use an NSI Rock Tumbler

••• greenbeads image by TekinT from

Budding young Earth scientists deserve educational toys as much as chemists or rocket scientists. One favorite toy is a small rock tumbler, such as the one made by NSI. Tumbling rocks to a glossy finish demonstrates the principle of mechanical erosion, while also teaching your child that geological processes are slow.

As a hobby, rock tumbling is not merely educational. Once the experiment is complete, the tumbler delivers a fistful of shiny stones to keep as cool science souvenirs or to use for jewelry, crafts and games.

    Wash the rock samples included with the kit to remove soil, then remove the barrel cover and place the rocks inside it, along with the kit's coarse grit. The coarse grit bag is marked "Step1." Add enough water to just barely cover the rocks.

    Replace the barrel cover and lock it in place. Start the motor and place the barrel in its cradle.

    Check the barrel after two days of tumbling--the rocks should have lost all their rough edges and sharp corners. If not, top off the water (if needed) and continue tumbling with the coarse grit.

    Tumbling removed all the rough edges and sharp corners from these stones.
    ••• stone image by chrisharvey from

    Pour off the dirty water and empty the stones from the tumbler. Rinse the tumbler and the stones thoroughly to get rid of all the grit.

    Return the smoothed stones to the barrel and add the medium grit, from the bag marked “Step 2.” Add water as before and tumble the contents for 12 to 14 days. Stop the barrel every two to three days and top off the water, if needed.

    Rounded, smooth stones after the second tumbling stage.
    ••• STONES image by brelsbil from

    Pour off the dirty water and grit, then empty the stones from the barrel. Scrub the tumbler thoroughly and wash the stones to remove all of the grit. Set aside any stones that broke during the tumbling.

    Return the stones to the tumbler with enough water to cover them and tumble for two to three hours to remove any remaining grit. Empty the barrel again and wash both the barrel and the rocks.

    Place the stones in the barrel again, along with the polish from the bag marked “Step 3.” Add water to just below the top layer of stones and tumble for another seven to eight days.

    A nicely polished agate, just right for a pendant.
    ••• stone image by Zbigniew Nowak from

    Remove the stones from the tumbler, then wash and dry them.

    Things You'll Need

    • Tumbler refill kit (raw stones and grit)
    • Water


    • The tumbling times given here are guidelines. The amount of time necessary to tumble stones is controlled by the sizes and types of stones in the NSI refill.


    • Do not pour the grit into the sink; it can easily clog the drain.


About the Author

Kelvin O'Donahue has been writing since 1979, with work published in the "Arizona Geological Society Digest" and "Bulletin of the American Association of Petroleum Geologists," as well as online. O'Donahue holds a Master of Science in geology from the University of Arizona, and has worked in the oil industry since 1982.

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