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Rotary rock tumblers – the ones with a drum that turns – are the most common type of tumbler used by lapidary hobbyists. They can turn rough rocks into beautifully rounded, polished gemstones. They do this by simulating a natural geological process that happens in rivers and streambeds – erosion.
Rotary rock tumblers are filled with raw stones, water, and grit. As the barrel turns, the stones and grit rub and grind against each other. Any sharp, pointy parts of the stones are worn down by the abrasion and tumbling action, and the surfaces of the stones are smoothed.
Experimenting with a rotary rock tumbler is a lot of fun. You learn more about geology and are rewarded with gorgeous gemstones that you found yourself! To get the best results, it helps to understand exactly how rotary rock tumblers work. Here, we discuss what rotary tumblers do, how they work, and which one is the best.
If you are interested in checking out the best rotary rock tumbler you can find it by clicking here (Amazon link).
What Is A Rotary Rock Tumbler?
A rotary rock tumbler is a machine used by lapidarists and gemstone hobbyists to smooth and polish rocks and gemstones. Not all rotary rock tumblers are large, commercial-sized machines. There are a number of small, high-quality tumblers on the market that process 2-to-3-pound loads of rock.
If you enjoy rockhounding, a rotary rock tumbler is an excellent investment. You can buy a durable one online for between $70 and $150. They are fantastic educational toys for children.
What Does a Rotary Rock Tumbler Do?
Rotary rock tumblers turn raw, angular chunks of rock into smooth, rounded pebbles. They do this by mimicking the natural process of water erosion, whereby rocks in stream beds are worn down into rounded pebbles and cobbles.
They are used to process hard rocks, like agate, jasper, amethyst, tiger’s eye, chalcedony, petrified wood, and quartz. Other materials like glass can also be worked in a rotary rock tumbler to make DIY sea glass.
Rockhounds collect rough stones in nature, and when they take them home, they can tumble them into polished specimens. Rough rocks do not always look that impressive, but when you tumble them, you enhance their inner beauty.
Natural water erosion takes hundreds, even thousands of years. Rock tumblers speed up this geological process so that we do not have to wait millennia to see the magic inside the stones we collect.
How Does a Rotary Rock Tumbler Work?
Rotary rock tumblers are designed to stimulate and accelerate the natural process that rounds and polishes pebbles in rivers and streambeds. But how do rock tumblers do this?
Rotary rock tumblers consist of a rubber barrel and a motor that turns it. Some models have different speed settings and a timer, while others are single-speed and only have an on/off switch.
As the barrel of the rock tumbler turns, the rocks inside grind against each other over and over again. Small bits of sediment break off, especially on the rocks’ edges and points. The longer you run the rock tumbler, the smoother and more rounded the stones inside becoming.
Tumbling rocks is quite a noisy process. You may want to keep the rock tumbler in your garage, basement, or garden shed while it is running so that you do not suffer noise pollution.
Eventually, when the process is complete, you open the rock tumbler to find your polished stones covered in a slurry of water and sediment. When you rinse them off, the colors, patterns, and crystals inside the rocks are revealed.
TIP: What Rocks can be tumbled together? Even if you are a beginner or a professional, there is always that curiosity about which rocks can be tumbled together. Find out the answer in the article below:
What Rocks Can Be Tumbled Together: Complete List With Tips
How To Use A Rotary Rock Tumbler?
Rotary rock tumblers, especially models that are designed for hobbyists, are super simple to use. Besides the rock tumbler, you do require a few other materials and bits of equipment to polish gemstones:
- Tumbling grit. Coarse, medium, fine, and polishing grit, depending on how shiny you want your specimens to be. Silicon carbide grit enhances the abrasion inside the tumbling barrel, working a bit like sandpaper. Coarse grit helps to wear the rocks’ edges and points down, shaping them. The finer grits help to smooth the surfaces of the rocks and polish them.
- Tumbling media. Plastic tumbling pellets, ceramic pellets, or walnut shells are added to the rock tumbler barrel along with the rocks, grit, and water. They cushion the rocks as they crash into one another as the barrel rotates, preventing the specimens from chipping, cracking, or breaking. They also help to increase contact between the grit and the stones.
- Colander or coarse sieve. You need this to rinse the slurry off the rocks once they have finished tumbling.
Once you have gathered everything you need to use your rotary tumbler, follow these steps:
Rock Tumbling Phase 1: Shape
- Fill the barrel of the rock tumbler two-thirds of the way full of rough stones. Rocks that are between about 3/8 inch and 1 1/4 inches in diameter work best. The largest rock you add should be no wider than half the diameter of the tumbler barrel.
- If you do not have a large enough quantity of raw rocks to fill the barrel, add tumbling media like plastic or ceramic pellets. It also helps to use pellets if the rocks are flat in shape or are a bit lower down on the Mohs hardness scale.
- Add 2 tablespoons of coarse tumbling grit for every pound of rock in the barrel. If you use too little grit, the rocks will take extremely long to be shaped.
- Fill the barrel up with water so that the rocks are just covered. Screw the lid tightly shut and wipe away any drops of water on the outside of the rock tumbler barrel.
- Connect the barrel to the rock tumbler, plug the machine in and switch it on.
- After running it for a week, switch the rock tumbler off, open the barrel and check if the rocks are the shape that you would like them. If you would like them slightly more rounded, run the machine for another few days. If you are happy with them, use a colander to rinse off the slurry. Do not let it go down the drain! You will ruin your plumbing. Rather find a better place to dump the wastewater.
- Clean the barrel thoroughly with soap and water before moving on to the next stage of tumbling. You want to get every bit of coarse grit out of the barrel so that it does not interfere with the next stage of tumbling.
TIP: If you need to cut your rocks to fit the tumbler, you can use a lot of different tools. Check out the best tools for cutting rocks in the article below:
What Can I Use to Cut Rocks? These 5 Tools are the Best!
Rock Tumbling Phase 2: Smooth
- Add the cleaned rocks and tumbling pellets back into the empty barrel.
- Add 2 tablespoons of medium grit for every pound of rock.
- Fill the barrel up with water as you did in the first tumbling stage and switch the machine back on.
- After running it for another week, switch the tumbler off and open up the barrel. You should see that any scratches, cracks, or pits on the rocks have been smoothed. Rinse them off thoroughly using the colander.
- Clean your whole set-up again, as before, getting rid of all the grit.
Tumbling Phase 3: Pre-polish
- Next, fill the barrel up with the rocks, tumbling pellets, and 2 tablespoons of fine grit per pound of rock. Add enough water to cover the stones.
- Let the rock tumbler run for another week.
- At the end of this phase, the stones should be silky smooth and develop a bit of luster.
- Clean off the stones and clean the whole set-up once more, as before.
Tumbling Phase 4: Polish
- Add the clean rocks, plastic tumbling pellets, and 2 tablespoons of aluminum oxide powder per pound of rock to the barrel.
- Fill the barrel up with water. Let the machine run for yet another week.
- After this phase, your specimens will be glistening!
Optional Phase 5: Burnishing
- If you want to bring out even more brightness in the rocks, you run the rock tumbler for another day. But instead of using polishing grit, add laundry powder or borax to the barrel.
- Clean the rocks and barrel thoroughly after the polishing phase before putting them back into the machine.
- Use 2 tablespoons of powder for every pound of rock. Be sure to use clean plastic tumbling pellets to prevent the rocks from chipping or cracking.
- After letting the rock tumbler run for another 24 hours, your specimens will come out sparkling.
TIP: Now to you know what all phases of rock tumbling are. So you might be interested in how expensive rock tumbling is. Check out the complete cost breakdown in the article below:
Is Rock Tumbling Expensive? Complete Cost Breakdown
Best Rotary Rock Tumblers
A small, 2 or 3-pound barrel rotary rock tumbler is the perfect type to get as a first-time user. But with the sheer number of various brands and models to choose from online, it can be overwhelming to pick one!
Here, we present the two best rotary rock tumblers. They are high quality, great value for money, and are available on Amazon.
Best Option: National Geographic Platinum Series Rock Tumbler (Amazon link)
National Geographic has made rock tumblers as high-quality educational toys for many years. The Platinum series model (Amazon link) is a miniature professional rock tumbler. The kit comes with everything you need – grit, polish, 1 pound of rough gemstones, and even some jewelry settings.
The barrel has a 2-pound capacity. It is made of thick rubber to absorb the impact of the rocks crashing against each other. The motor has 3 different speeds and a timer so that you can set the number of hours or days the tumbler runs for.
The Platinum Series rock tumbler has a noise-reducing cover over the barrel. This helps to reduce the noise so that you can run the machine inside your house.
The machine is designed to prevent softer rocks from being damaged as they tumble. The rock tumbler has a patented “agitate mode” that has a gentler motion.
If you are interested in buying a National Geographic rock tumbler check out the latest prices here (Amazon link).
TIP: Rock tumbling is the perfect hobby for kids around 8 years or older. Are you looking for a rock tumbler for kids? Check out the complete guide in the article below:
Best Rock Tumblers for Kids in 2022: Options For Diff Ages
Alternative Option: Lortone 3A Single Barrel Rock Tumbler
The Lortone 3A rotary rock tumbler (Amazon link) is an excellent entry-level option. It is an economical size, with a 3-pound barrel capacity, and performs very well. It only has a single-speed, and there is no timer.
The barrel is made of thick, high-quality rubber that absorbs impact from the rocks as they tumble. It is quite loud while it is running, as there is no noise-reducing cover over the barrel.
The Lortone 3A tumbler has been designed to work for many years. It is not just another toy rock tumbler you can buy online. This rotating rock tumbler is sturdy and easy to operate.
One drawback is that you have to buy all the other materials you need to tumble rocks separately. This rock tumbler does not come with grit, polish, tumbling media, or rough rocks.
If you’re looking for a basic rotary tumbler that works well, this is the one for you. If you’re buying a rock tumbler for a child, a kit that comes with everything you need may be better.
How Long Does It Take To Polish Rocks In Rotary Rock Tumbler?
Unfortunately, polishing rocks in a rotary tumbler is a slow process. But remember, compared to the natural geological process, it is almost instantaneous!
To polish a batch of rocks in a rotary tumbler takes anywhere from 3 to 6 weeks. It can take more or less time – it depends on the type of rock, its hardness, and to what level of finish you would like it polished.
When you are buying a rock tumbler for a child, it is important to prepare them for how long the whole process takes from the beginning. Encourage them to have realistic expectations so that they avoid disappointment.
If you are interested in buying a Lortone 3A rock tumbler check out the latest prices here (Amazon link).
BTW: Do you want to know more about rock and mineral identification? The books listed below are the best ones you can find on the internet (Amazon links):
- Smithsonian Handbooks: Rocks & Minerals
- Gemstone & Crystal Properties (Quick Study Home)
- Ultimate Explorer Field Guide: Rocks and Minerals (National Geographic Kids)
Rotary rock tumblers are machines that process rough rocks into beautifully sparkling gemstones. They do this by replicating and accelerating the natural process of erosion that happens to pebbles and cobbles in riverbeds.
Rotary rock tumblers are easy to use, even for kids! All you have to do is fill the barrel with rocks, pellets, grit, and water and let it tumble away for weeks and weeks. As the barrel turns, the rocks rub and wear against each other. They become rounded and polished.
TIP: Rock tumblers require some maintenance, though, as you will need to oil them regularly to keep them running smoothly. Check out how to oil your rock tumbler in the article below:
Step-By-Step Guide: How To Properly Oil Your Rock Tumbler