Rock tumbling media can significantly improve the results of your tumbling and reduce the
amount of time needed to convert rough rock into brightly polished stones.
These small particles can deliver grit to hard-to-reach rock surfaces, reduce impact forces
in the tumbler barrel, cause rocks to tumble rather than slide in the barrel, and serve as
a filler when you don't have enough rocks to properly fill the tumbler barrel.
Ceramic media and plastic pellets can be valuable additions to your rock tumbling supplies kit.
They can save electricity, conserve grit and make you smile when you open your tumbler.
Here are four reasons to use plastic pellets or ceramic media:
Cushioning: To absorb impact energy in the tumbler
Particle Size Balancing: Add small particles to a load of large rocks
Filler: You don't have enough rough to fill the barrel properly
Improve Tumbling Action: Make the rocks in the barrel tumble better
Once you decide that you can benefit from using media you will still have some decisions.....
Should you use plastic or ceramic? Which size should you use? How many should you use?
These questions are difficult to answer because every barrel of tumbling rough is different. And,
two batches of agate can have different shapes, different particle sizes and different physical
properties. Sometimes you must experiment - that's how you learn and become an experienced tumbler
operator. But, here are a few general ideas to get your started....
Cushioning Fragile Stones
Some types of rough such as Apache Tears and Amethyst can bruise (develop tiny surface fractures from
impact) in the tumbler. Soft plastic pellets can absorb some of that impact energy and protect your stones.
You don't have to add a lot of pellets - just one or two rounded tablespoons per pound of rough can
reduce the impact forces that occur in the barrel. Avoid the temptation to make your
load 50% plastic pellets. If you do that you will significantly reduce the amount of rock-to-rock grinding
that occurs in the barrel - and your stones will make very little progress in the tumbler.
Keep in mind that one recipe will not work in every situation. Two different barrels of rough can contain
different materials, different particle sizes and different particle shapes. You may need to experiment
to achieve optimal results.
Plastic pellets work well in a rotary tumbler, however, they do not work well in a vibratory tumbler.
If your stones are getting bruised in a vibratory tumbler we recommend ceramic pellets with a particle
size that is smaller than the rough that you are tumbling. These will fill the spaces between the rough
and reduce the force of stone-to-stone impacts.
Particle Size Balancing
The rough in a properly loaded tumbler barrel will have a wide range of particle sizes. It might have
about 33% small rocks (1/4 to 1/2 inch), 33% medium rocks (1/2 to 1 inch) and about 33% large rocks
(1 to 1 1/2 inches). This particle size distribution is known as a "balanced load".
Grit and polish do their cutting when they are caught between hard pieces of rock in your tumbler. If your
three-pound tumbler barrel is loaded with a few large rocks there will be very few rock-to-rock
contacts where grinding can occur. However adding some small rocks to fill the spaces between
the large rocks will significantly increase the number of rock-to-rock contacts in the tumbler and result in more rapid grinding.
Ceramic media is often added when you don't have small size rough to balance the particle sizes in the
tumbler barrel. Add just enough media to fill the empty spaces between the larger rocks.
Filler
Do you have some really nice rough but not quite enough to bring your tumbler barrel up to the recommended
2/3 to 3/4 capacity. When you have that situation and are anxious to tumble just add some large ceramic
media and start tumbling. (Plastic pellets do not work as well as ceramic for this type of "filler".
The hard surfaces of ceramic media produce a better grinding action.)
Improve Tumbling Action in the Barrel
If you have rough with lots of flat pieces (such as trim-saw slabs) or lots of very angular pieces they
might slide in the barrel instead of tumbling. Adding a few ceramic cylinders might get those stones tumbling.
Ceramic cylinders act like roller bearings in the tumbler barrel. They get between flat and angular pieces of
rough and increase their motion. You don't have to add a lot - just a rounded tablespoon or two per pound of rough.
How Long Will Ceramic Media Last?
Ceramic media has about the same durability as agate or jasper. If you run them in coarse grit
large media will get smaller and smaller and be gone in a few weeks. Small media might last only
one or two weeks.
Ceramic media work best in the fine grit, polishing or burnishing steps. Used only in those
steps they will last for a very long time.
Don't Forget to Experiment
We hope the ideas above will help you decide when to use plastic pellets and ceramic media.
Don't be afraid to experiment. That's how you get experience and knowledge.
Ceramic and plastic tumbling media are used as a filler or as a cushioning agent in rock tumbling. This video shows how they work for the various applications in a rotary tumbler.
A guide to selecting tumbling media for rotary and vibratory tumblers in various situations.
Large ceramic media: These angle-cut ceramic cylinders are about 3/8" diameter x 5/8" long. They work great for filler when you have less rock than what is needed for the tumbling capacity of your barrel. Just add enough media to bring your barrel up to tumbling capacity. We use large ceramic media for filler because they last a lot longer then small ceramic media - and when their size is reduced you can use them as a substitute for small media.
Small ceramic media: These angle-cut ceramic cylinders are about 3/16" diameter x 3/8". They work great when you need some small-size material to balance the particle size load in your tumbler. They also work well when you have a lot of flat or angular-shaped rocks that tend to slide in the barrel instead of tumbling - they get between those rocks and serve as roller bearings!
Plastic pellets can be purchased in a range of sizes from about 1/8" up to about 1/4". Their main use is for cushioning fragile rocks in a rotary tumbler. Just a tablespoon or two per pound of rocks is usually enough - but you might experiment to see what works best in your situation. Plastic pellets usually don't work well in vibratory tumblers. The rapid action of the vibratory tumbler combined with the "bouncy" nature of plastic pellets can cause excessive motion in the tumbler.
A Few More Tips.....
Plastic pellets float. To separate them from your rock, place the rock in a bucket of
water - the plastic pellets will float to the top. You can scoop them up with a small fish net or tea strainer.
Grit can become embedded in plastic pellets. If you use plastic pellets with medium grit you should not reuse
them with fine grit - because some of the medium grit might be embedded in the pellets. Some people dry their used
pellets and save them in a labeled plastic bag until needed again.
Large ceramic pellets make great filler. Use large pellets for filler because they last longer.
Ceramic pellets can be rinsed with your rock and moved to the next step of the tumbling process. The same ceramic
pellets can follow your rocks all the way through the tumbling process.
Don't use plastic pellets in a vibratory tumbler. Instead of absorbing energy they will cause your rough to bounce
around the bowl. Use ceramic media in vibratory tumblers.
