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Buying Guide:
Rock Tumblers

Rock tumblers bring out the inner beauty of all types of rocks. They'll smooth the edges, enhance the natural coloring, and create glossy, high-end, professional-looking stones. The art of cutting, polishing, and engraving precious and semi-precious stones is called lapidary and has been used by professionals and hobbyists dating back to primitive times.

Today, most people use rock tumblers for jewelry making, display finds around the home, or just general geology education and fun. We've got tumblers in all styles and sizes for personal or commercial use. There are a lot of steps between raw rock and smooth stones - we'll help you understand the basics of owning and operating a rock tumbler and help you choose the best one for you.

By Rachel Haas

Rotary vs. Vibratory Rock Tumblers

Rotary Tumbler
A rotary tumbler consists of two parts - a barrel and a frame. The barrel holds a batch of rough stones and the abrasive materials used to smooth and polish them, and the frame uses a motor to rotate the barrel with a belt and pulley system. When the barrel spins, it carries rocks up the sidewall, creating a rotating waterfall of cascading rocks, causing them to bounce along the tops of other rocks, simulating the way that rocks gradually become rounded in a creek bed or on a bank. Although it takes years and years for this outcome to occur naturally, a rotary tumbler speeds up the process, taking only 4-6 weeks to fully shape and smooth a batch of chosen stones.

Rotary Rock Tumbler
Rotary Rock Tumbler

Vibratory Tumbler
This type of tumbler shakes up the process. The vibratory tumbler has a lidded bowl instead of a barrel and a base that vibrates. The vibration creates friction between the rough stones and abrasive material, causing the stones to wear down into smooth and polished shapes. Because the stones are moving in a fast, agitated motion, rather than a slow tumbling motion, the stones will retain their angular shape rather than taking on a smooth, rounded shape like in a rotary tumbler.

Choosing a Size

Barrels and bowls come in different sizes, so it is important to consider how large your batches will be and the size of rough stones that you'll likely be tumbling. If you're taking up lapidary as a hobby or an educational activity for the kids, you'll most likely want a barrel with a 3- to 6-pound capacity. A 3-pound barrel is perfect for stones measuring 3/4 to 1 inch in size, but can be somewhat limiting if you have a larger stone here and there that you would like polished. A great mid-sized option is the 4-4.5-pound capacity barrel, which can tumble stones up to 3.25 inches (about the size of a tennis ball), and the 6-pound barrel can go larger than that. One thing to keep in mind is that in order for it to work, you must be able to fill the container 2/3 - 3/4 full, so bigger is not always better when choosing a barrel or bowl size.

A double-barrel tumbler can be a convenient option, as it provides a little more versatility in batch sizes. You can use one or both barrels (or bowls) at a time, depending on how many rocks you have. You can also speed up your process a bit by running two batches simultaneously. It's also good to note that barrels with all-rubber constructions are the quietest and least disruptive.

Selecting Stones

Our incredible Earth has provided a near-infinite selection of beautiful stones, and experimenting with different colors, sizes, and textures is part of the fun. It's important to note that not all stones will be glossy after tumbling. A good indicator of what a stone will look like when finished is how it looks wet. If a stone has a glassy texture when wet, then it will most likely look that way when finished tumbling. A stone's hardness and texture will determine its finished look. Soft and porous stones will not likely shine. Stones that are higher on the hardness scale, like jasper, will become quite glossy. Also keep in mind that stones with more angular shapes or cracked surfaces will take much longer to smooth than stones that have already become somewhat rounded naturally, like those found in a river bed.

Make sure that all stones within a batch have about the same hardness and condition as each other in order to finish at the same rate. You don't, however, want them to all be exactly the same size. Having various sizes of rough rock allows the abrasive material to better distribute.

India Amethyst Tumbling Rocks
India Amethyst Tumbling Rocks
Abrasives and Polish

There are many types of abrasive material used for rock tumbling. A different abrasive will be used in each stage of the tumbling process, starting with the most course and ending with finest grade. Here is a guide as to what grades of abrasives are generally used for each stage.

  • Step 1: Grinding and Shaping
    Normally 60/90 SiC abrasive
  • Step 2: Smoothing the Surface
    120/220 SiC abrasive
  • Step 3: Pre-polishing
    Aluminum Oxide Pre-Polish (although finer grades of silicon carbide, such as 600 grade can be used)
  • Polishing
    Aluminum Oxide Pre-Polish (although finer grades of silicon carbide, such as 600 grade can be used)

Plastic pellets are also used in the tumbling process as filler when your batch doesn't quite meet the 3/4 or 2/3 line in stage 2, and it is also used to help cushion stones during pre-polish and polishing stages. If washed thoroughly, plastic pellets can be used many times over. However, you do not want the wrong kind of abrasives being inadvertently transferred to different stages, so it's helpful to keep four separate containers of plastic pellets, each one to be used in only one stage.

Tumbling Media Quantities
Barrel Size Capacity
(Max Volume)
Step 1:
Coarse Grind
Step 2:
Medium Grind
Step 3:
Pre-Polish
Step 4:
Polish
Step 5:
Burnish (Soap)
Pounds Cups Level Teaspoons
1.5 1 3/4 4 4 5 5 1/4
3 3 4 4 6 6 1/4
4 5 8 8 8 8 1/2
Rock Tumbling Media
Rock Tumbling Media
Setting It Up

It's important to always read the instructions included with your rock tumbler for the best possible outcome.

Rock tumblers are designed to operate 24 hours a day for several weeks at a time. Place your tumbler in a space that will be out of the way yet accessible enough to check on periodically. You may want to place a cookie sheet or wide pan underneath to catch any accidental spillage that may occur. Place in a sheltered location - garage, enclosed porch, laundry room, - and ensure that it stays out of the sun and away from severe temperatures. Sun exposure and cold temperatures can shorten your tumbler's life span and cause cracks or leaks. Do not place in a small, enclosed space such as a cabinet, rock tumblers need ventilation and can become quite warm.

Things you will need:

  • Rotary or vibratory tumbler with barrel
  • Stones of similar hardness in various sizes
  • Abrasive material - course, medium, pre-polish and polish compounds
  • Plastic Pellets (optional)
  • Fine-meshed colander - to simplify cleaning between stages

Be sure to never wash the pebbles and abrasive material down your plumbing system

The Five Stages of Rock Tumbling:

Stage One: Grinding and Shaping
(Rotary 7-10 days, Vibratory 1-2 days)

This is the most important step. Course abrasives grind and shape the stone to remove rough edges, cracks and divots from the stones. The most material is removed from the stones in this step. It will be complete when the stones are the desired shape with no cracks or flaws. Remember that while a rotary tumbler will round out the edges, a vibratory tumbler will keep the stones' angular shape.

Open the barrel and fill with your chosen stones until 2/3 full. If it is too full, the stones won't tumble, if it is not full enough, it may take an extra day or two.

Add your course silicon carbide abrasive, checking the chart for the correct amount. Slowly add water until it just covers the top of the stones. Seal the barrel according to your tumbler's instructions (avoid over-tightening, as it could lead to warping).

Turn on the tumbler and place the barrel on the base. Watch for a few minutes to ensure that it is working properly and that there are no leaks. If leaks occur, clean the lid and gasket surfaces thoroughly and try again.

Run the tumbler for about one day, and then open to release gas build-up.

The abrasive material and water will have formed a mixture called 'slurry'. If the slurry appears to be thick and pasty, add a little more water. Remove a couple stones, rinse and you should see some slight rounding.

Reseal the barrel, let run for another day and check again. With a vibratory tumbler, you will be ready for the next stage. You will repeat this process 7-10 days with a rotary model. When all the stones are smooth and rounded, they will be ready for the next step.

If the stones are not as smooth as desired at this point, you will need to clean the stones and barrel and use fresh abrasives, as the original abrasives will have broken down.

Pour the slurry into a bucket over a mesh colander to sift out all of the abrasive material. DO NOT POUR DOWN THE SINK.

Now thoroughly wash the barrel and stones so that all abrasives are completely gone. Any course abrasives hiding in cracks and pockets will contaminate the next step. Keep a close eye on the edges and lid to ensure that there are no stowaways.

Stage 2: Smoothing - Medium Abrasive
(Rotary 7-10 days, Vibratory 2-3 days)

Place your stones back in the barrel, and add the appropriate amount of medium-fine silicon carbide abrasive, according to the table.

If the barrel is less than 2/3 full, add plastic pellets to add to the volume. Add water and seal just as in step one.

This time you'll tumble for 2 or 3 days before checking the stones. If using a vibratory tumbler - clean the bowl, your batch is ready for the next step.

Rotary tumblers - on the seventh day, rinse and check the stones. They should have a uniform, smooth look and matte finish.

Clean the barrel exactly as you did in stage one.

Stage 3: Pre-Polish - Aluminum Oxide Pre-Polish
(Rotary 7-10 days, Vibratory 2-3 days)

As in stages 1 and 2, fill the barrel with stones until 2/3 full, using plastic pellets as filler if needed.

Add water so that it just covers all of the stones.

Carefully seal the barrel and tumble for 2-3 days in a vibratory tumbler or 7 days in a rotary tumbler.

Check and remove any chipped edges. The stones should have a slight shine by now. If not, allow them to tumble for an extra 1 to 3 days.

Now clean the stones and barrel as you did in the last 2 stages.

Stage 3: Pre-Polish - Aluminum Oxide Pre-Polish
(Rotary 7-10 days, Vibratory 2-3 days)

Ensure that the stones are completely clean - contamination is the main cause for an undesirable result.

Carefully fill the barrel 2/3 full with your stones, adding plastic pellets if needed.

Add water and the right amount of polish according to the chart.

Let tumbler run for 2-3 days in a vibratory tumbler, or 7 days in a rotary tumbler, and then inspect the stones. At this point, the stones should be glossy and shiny.

Clean the barrel carefully and move on to stage 5.

This is an optional step that removes any residual evidence of polish on the stones. In this stage, tumble the stones with a small piece of bar soap or two drops of liquid hand soap for 12 hours. Remove stones and rinse thoroughly.

Rotary vs. Vibratory Tumblers

If you're still not sure which type of tumbler will work best for you, use this list of the basic differences in your decision.

Rotary Tumbler

Advantages:

  • Easy to use, great for beginners
  • Creates nice rounded stones out of rough rock
  • Runs quietly when using a rubber barrel
Vibratory Rock Tumbler
Vibrating Rock Tumbler

Disadvantages:

  • Longer tumbling times (4-6 weeks total)
  • Requires more abrasive material
  • Occasional leaks may occur

Vibratory Tumbler

Advantages:

  • Shorter tumbling time (1.5-3 weeks total)
  • Requires less abrasive material
  • Gentile process, better for fragile rocks
  • Won't leak

Disadvantages:

  • Won't round rough rocks - although this could be considered an advantage if you prefer a natural, angular shaped stone
  • More challenging to use
  • Generally more expensive
  • Noisier
  • Vibrating can cause them to move on their own, or create a buzzy sensation in your building, you may need to weigh them down or attach them to something.

Rock tumbling is a fun way to learn about and uncover nature's beauty, whether you're a beginner or if you're working at a professional level. Hopefully this information has helped you decide what type and size of tumbler is best for you. In most cases, you get what you pay for; a higher-quality tumbler will last longer and achieve more desirable results. The same goes for the material that you tumble. Enjoy your search and happy tumbling!

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