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Rock Tumbling Media: How Much and What Kind to Use

Rock Tumbling Media: How Much and What Kind to Use
A batch of tumbled rocks with ceramic media strewn out on a table

When my daughter and I bought our rock tumbler and were going through the tumbling process for the first time I noticed that the barrel became less full at every step. The tumbler we bought came with instructions but it didn’t mention the need for any tumbling media. After tumbling more batches of rocks and doing extensive research I now know that adding tumbling media is an absolutely essential part of the rock tumbling process. But how much tumbling media should you use, and what types of tumbling media work best?

The amount of rock tumbling media to use depends on the size of the tumbler barrel and the amount of rock being tumbled. After adding the rocks to the barrel, use enough tumbling media to make it 3/4 full. The best and most common types of tumbling media are ceramic cylinders and plastic pellets.

The complete answers to these questions is a little more nuanced. I’ll get into exactly how much tumbling media to use, when its needed, and why. I’ll also break down what the two types of tumbling media are typically used for and why they’re used in those applications. By the way, if you are still relatively new to the hobby and want to take all of the guesswork out of the process, I highly recommend checking out my complete step-by-step guide.

How Much Tumbling Media to Use

At the beginning of the tumbling process, you may begin with enough rocks to fill your barrel, but as the rocks become more worn down and smooth you will undoubtedly notice that they don’t fill the barrel up as much in subsequent steps. That’s when tumbling media really becomes essential.

Fill the Tumbling Barrel

Making sure your tumbling barrel is filled to the right level is one of the most critical parts of every step in the tumbling process. For the best results, it is imperative that your barrel be 2/3 to 3/4 full – I’d recommend leaning towards 3/4.

Filling the barrel to the appropriate level improves the tumbling action of the rocks and protects them from damage. If the barrel isn’t full enough the rocks won’t tumble properly, and if it’s too full they will barely move around in the barrel at all.

Use Tumbling Media for Size Variety

In addition to adding volume to the tumbling barrel, tumbling media is also used to improve the size distribution of material being tumbled. If you are tumbling a lot of rocks that are close to the same size, there will be relatively few points of contact between them. This is especially true for batches containing only larger rocks.

Because you want more points of contact between the rocks for improved grinding action, you may want to add tumbling media even if it’s not to increase the volume of material in the barrel. Add enough media to fill in the void spaces between the larger rocks. This won’t make the pile of rocks any larger in the barrel but it will definitely improve the results.

Mix the Tumbling Media In

On that note, you want to make sure to mix the tumbling media in with the rocks. Don’t just pour it on top and hope it’s good enough! After adding your rocks to the barrel, pour the tumbling media on top. Then shake the barrel around and maybe stir it up with your fingers to get the media to settle in between the rocks. Keep repeating this process until the rock/media mixture is at the 3/4 full level.

What Type of Tumbling Media to Use

There are really only two main types of tumbling media from which people choose: ceramic cylinders and plastic beads. Some people use other materials like walnut husks in certain circumstances, but I wouldn’t recommend exploring those fringe cases until you are well versed in the hobby. I’ll cover ceramic and plastic media here, and when to choose each type.

Rotary vs Vibratory Tumblers

If you’re reading this article then chances are you’re using a rotary tumbler. Vibratory tumblers tend to be used by more experienced hobbyists and professionals. If you want to read all about the differences then I’d recommend my article on the subject.

If you’re using a rotary tumbler then you can use ceramic or plastic tumbling media, but if you’re using a vibratory tumbler then plastic pellets are out of the question. The beads don’t work well in vibratory tumblers because they are a little too ‘cushiony’ and they prevent the rocks from moving properly in the barrel.

Check Your Rock Size Distribution

As I mentioned above, you want a good distribution of rock sizes in your barrel for the best tumbling and grinding action. If you need to add tumbling media for a better size distribution then you’ll want to use ceramic media.

Ceramic media is hard enough that it will add to the grinding process when it makes contact with the rocks. The plastic beads are too soft and squishy to adequately contribute to the grinding action, so if you tried using them for this purpose you’d likely be sorely disappointed.

Transferring Media Between Steps?

Another factor to consider is whether or not your want to be able to transfer your media between tumbling steps. Ceramic media has the benefit of being able to be transferred through every step of the tumbling process along with the rocks (provided that everything is sufficiently rinsed and cleaned).

Plastic pellets are pretty soft, which allows tumbling grit and bits of rock to become embedded in the pellets. If you tried transferring them between steps your batch of rocks would be very dull and disappointing. Instead, you can save them in a container to be used on the same step of a different batch. One advantage of plastic pellets is that they float in the slurry, making them easy to scoop out at the end of each step.

Use Different Media Types for Different Steps

You don’t necessarily have to use the same type of tumbling media on every step. Depending on what you’re trying to accomplish with each step and the type of rocks you’re tumbling, you may want to switch between media types as you move through the tumbling process.

For example, you may choose to use ceramic media in the first two steps because that’s where the vast majority of the shaping of the rocks occurs. The increased contact points and grinding action from the ceramic is much preferable to the soft plastic pellets if you want very well-rounded rocks. Then you may choose to switch to plastic pellets to cushion and protect the rocks from damage in the later steps.

The Bottom Line

Use ceramic tumbling media if the primary goal is to create better tumbling and grinding action to create well-rounded rocks. Plastic pellets are a better tumbling media to protect delicate rocks in later tumbling steps. If using a vibratory tumbler then you should only use ceramic tumbling media.

The ceramic media I personally use and recommend is these ceramic pellets from Polly Plastics (link to Amazon). I’d recommend getting 3 pounds worth because I often find that one 1.5 pound bag isn’t quite enough. These pellets are all the same size which works just fine, but some people prefer the version with mixed sizes of pellets. While I have not personally used them, many people swear by Polly Plastic’s plastic pellets. I’ve had really good results with Polly Plastic products so if I were ever going to try using plastic pellets these would be the ones.

Purpose of Tumbling Media

I’ve touched on this a bit earlier in the article but I think it bears some more discussion. Tumbling media serves more than one function in the rock tumbling process, each of which is integral to getting the best final results. There are three primary purposes of rock tumbling media:

Protect Rocks from Damage

Tumbling media fills the barrel of the rock tumbler up enough to prevent the rocks from falling too far and too quickly. This is especially true in the case of plastic pellets, which are softer than ceramic media and therefore cushion the blows between rocks more effectively.

Better Tumbling Action

When tumbling media fills the void spaces between rocks it creates a more ‘fluid’ mix of rocks and media. That mix tumbles more smoothly and effectively than rocks would on their own. Without the tumbling media, the rocks tend to tumble more erratically because they fit together like mismatched puzzle pieces.

Increase Contact Points

One of the most important roles of tumbling media is to increase the number of contact points on the rocks. When tumbling grit gets pinched at those contact points it wears on the rocks, which is the process we’re looking to create in each tumbling step. The more contact points there are in the barrel the more effectively the rocks are smoothed. This is especially true for ceramic media which is hard enough for the rocks to grind against.

Recommended Equipment

If you’re new to rock tumbling or are wondering how to take your game to the next level I suggest taking a look at my recommended gear page. There you’ll find full reviews and recommendations on my favorite rock tumbler and rock tumbling accessories, as well as a lot of gear I use when rockhounding in the field.