Plastic Pellets & Ceramic Media in Rock Tumbling
Why Use Rock Tumbling Media?
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
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, obsidian, amethyst and rose quartz can bruise (develop tiny surface fractures from impact) in the tumbler. In a rotary 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.
Do you have some really nice rough but not quite enough to bring your tumbler barrel up to the recommended 1/2 to 2/3 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.)
We use large ceramic cylinders for filler because: they are usually cheaper per pound, they last longer than small cylinders, when they get smaller we use them where small cylinders are needed.
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. Small cylinders work best because they can more easily get between flat slabs and angular pieces.
How Long Will Ceramic Media Last?
Ceramic media is just a little more durable than agate or jasper. If you run them in coarse grit, ceramic media will get smaller with every tumbler run. Small media might last just a few weeks in coarse grit. Large media lasts a lot longer.
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.
What Do We Use?
Our first choice for filler is rocks that have been previously tumbled and still need a few weeks of grinding to arrive at a great shape. They are already rounded so they can improve the tumbling action of angular rough. If we don't have rocks to grind on hand then we consider using media.
We stopped using plastic pellets a few years ago. We didn't like capturing them after each grit size and storing them for next time. We think that it is a lot more efficient using ceramic media because you simply rinse it with the rocks and use it with the next step. No more fishing for pellets and saving them in baggies.
We use large ceramic cylinders most of the time. They cost less and last a lot longer. The only time we use small cylinders is when we have serious cushioning concerns. Then we use large cylinders that have been reduced in size.
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.
- Be careful when purchasing. Ceramic media is sold for a wide variety of purposes and some of it has embedded abrasive grains. All of the media that we sell is smooth aluminum oxide and does not contain any abrasive.