How do I tumble rocks, and how long does it take?

You tumble rocks by running them in a closed barrel with water and a series of ever-finer abrasive grits, washing everything clean between stages, and finishing with a polish. In a rotary tumbler that takes four stages and, by the published manufacturer and supplier schedules, roughly three to five weeks of running time for a batch of hard stone like agate or jasper, longer when the coarse stage has to be repeated. A vibratory tumbler is faster per stage but cannot do the first, coarse stage on angular rough. The steps below follow published instructions from Lortone, Kingsley North and Thumler's, with grit sizes, amounts and times, plus what to keep out of the barrel and how to handle slurry.

Rotary or vibratory

Most people start with a rotary tumbler, because it does the whole job from rough to polish. Dated list prices for both kinds are on equipment at the next size.

Choosing rough

Pick stones that are hard, solid and similar to each other. Kingsley North's instructions call for stones of similar size and grading in each barrel [2]. A soft stone in a barrel of hard ones wears away before the hard ones are shaped, and a fractured stone breaks and scratches everything else.

Good first rough: agate, jasper and other chalcedony, all quartz-family stones near 7 on the Mohs scale (the hardness scale is explained on testing hardness with the Mohs scale). Buy or collect enough to fill the barrel: Lortone says to fill it about half to two-thirds full [3]; Kingsley North says 2/3 to 3/4 [2]. Include a range of sizes so the stones tumble against each other rather than sliding as one mass.

The four rotary stages, by source

The two published schedules agree on the shape of the process and differ in the details. Both are below; follow the one written for your machine, or the supplier you buy grit from.

Adding up the stage times (this page's arithmetic; neither source states a total): Kingsley North's gives about four to five weeks for a batch that goes through each stage once, longer when the coarse stage has to be repeated, which it often does on rough that starts angular. Lortone's 5 to 7 days per stage over four stages gives about three to four weeks.

How much grit

Both sources give grit by barrel size. Lortone, for its larger barrels [3]:

Kingsley North, for hobby-size barrels, in tablespoons [2]:

Running a batch, step by step

1. Load the barrel with rough to the level your instructions give (half to two-thirds for Lortone [3], 2/3 to 3/4 for Kingsley North [2]). Do not exceed the barrel's rated capacity [3].
2. Add the coarse grit in the amount for your barrel size.
3. Add water until it just reaches the top layer of stones. Lortone says to add water to the top layer of rocks and abrasive, and "Do not overfill" [3]; Kingsley North says to add it until it just touches the bottom of the top layer of stones, because too much water inhibits tumbling [2].
4. Seal and run. Wipe the barrel's mating surfaces and gasket before closing, and do not use tools on the wing nuts; over-tightening can damage the lid, gasket and barrel [3].
5. Vent gas. Open the barrel occasionally to release gas that can build up during tumbling [3]. Kingsley North says to open it after the first 24 hours of the coarse stage [2]. Thumler's notes that glass, natural or man-made, can produce gas [1].
6. Check the slurry. If it is thick and pasty, add a little water and check again after an hour [2].
7. Wash everything between stages. Kingsley North: "After the 1st grind, you must clean the barrel and stones thoroughly to remove all traces of the coarse grit slurry" [2]. Coarse grit carried into a finer stage leaves scratches the finer grit was meant to remove.
8. Top up the volume. As stones wear down, the barrel empties. Add plastic pellets (Kingsley North) or ceramic media to bring the load back to the right level; pellets also cushion the stones in the polish stage [2].
9. Judge the finish. Kingsley North's test: if the stones look the same wet and dry, the batch is finished [2].

Vibratory tumbler schedule

Thumler's instructions for its UV-10 and UV-18 vibratory tumblers [1]:

• Step 1, medium grit: 6 tablespoons in a UV-10, 10 in a UV-18. Run 48 hours, rinse, recharge with the same amount and repeat until the stones reach the shape you want.
• Steps 2 and 3, fine grit then polish: 3 tablespoons in a UV-10, 5 in a UV-18, 2 to 3 days each.
• Water: just enough for the grit to cling to the rocks and media; small, irregular rough needs two or three times more than large, smooth stones. Check at least twice a day.
• Loading: mix particle sizes, use ceramic media if you lack small pieces, and fill to just below the top of the center structure.

What not to tumble

• Soft stones in a hard batch. They wear away before the others shape up. Tumble soft material separately, if at all, and keep each batch to stones of similar size and grading [2].
• Water-soluble and water-sensitive minerals. Halite, selenite and others on minerals that must not get wet dissolve or degrade in a wet barrel.
• Minerals with toxic elements. The NPS lists twelve elements of concern, including arsenic, lead and mercury, and warns that "Inhaling mineral dust may be more of a hazard than handling the specimen" [4]. Grinding them in a barrel puts those elements into the slurry you then handle and dispose of. See which minerals are dangerous.
• Asbestiform and radioactive minerals. Never. See asbestiform minerals and radioactive minerals at home.
• Fractured or porous rough. It breaks, and porous stones hold grit from one stage into the next.
• Glass, unless you plan for gas. Thumler's warns that it can produce gas in the barrel [1].

Slurry: never down the drain

Both rotary sources agree on this. Lortone says rinse water must not go into a household drain because it will clog it [3]. Kingsley North: "Do not pour slurry into your plumbing system, it will settle in the pipes and harden like cement" [2].

Rinse stones and barrel into a bucket kept for the purpose, outdoors or in a utility area. Let the solids settle, and ask your local waste authority how to dispose of them. Keep slurry wet until it is disposed of: dried slurry from quartz-family stones is a source of fine silica dust, and OSHA's rule for employers prohibits dry sweeping where it could contribute to exposure [5]. Clean up spills with a damp cloth or mop, not a broom. The dust numbers are on silica dust.

Noise and where to put it

A tumbler runs day and night for weeks. Thumler's says that running only large rough is a common cause of noise in its vibratory machines and recommends mixing sizes or adding ceramic media [1]. None of the instructions cited here gives a decibel figure. Put the tumbler in a garage, basement or outbuilding on a surface that does not amplify vibration, away from bedrooms, and check that the outlet and circuit are sound before you leave it running; Lortone tells you to make sure the unit is plugged in correctly and the circuit works [3].

What to do with a barrel of polished stones

A finished batch is a jar of small stones that needs sorting, storing and, if you sell them, labeling as a lot. How to store loose tumbled stones is on gem jars and small lots. If the stones are going into a teaching set for children, the choice of species and the federal rules start on building a teaching set.

References

1. Thumler's Tumbler, instructions for UV-10 and UV-18 vibratory tumblers (undated; copy hosted by content.cmpl.org, read October 22, 2026). https://content.cmpl.org/tg/Hobby/RockTumbler.pdf
2. Kingsley North, *Rotary rock tumbling instructions* (page copyright 2026, read October 22, 2026). https://kingsleynorth.com/pages/rotary-rock-tumbling-instructions
3. Lortone, Inc., *Instructions and Parts List, Lortone Rotary Tumbler, Models C40, C20-2 and C20*, copyright 2008 (copy hosted by Rio Grande). https://riogrande.com/globalassets/knowledge-hub/instruction-sheets/rotary-tumbler-instructions-and-parts-list-is-3.pdf
4. National Park Service, Greg McDonald, *Health and Safety Issues with Geological Specimens*, Conserve O Gram 11/11, September 2006. https://www.nps.gov/subjects/museums/upload/11-11_508.pdf
5. Occupational Safety and Health Administration, 29 CFR 1910.1053, *Respirable crystalline silica*, via Cornell Legal Information Institute, read October 22, 2026. https://www.law.cornell.edu/cfr/text/29/1910.1053