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Ceramic Tumbling Media Can Improve Your Tumbled Stones

Rock tumbling media
This is a small scoop from our media bucket. As you can see we have a range of different sizes of ceramic media. We believe that using a range of sizes of media works well for our needs. You probably also noticed some stones. These are small stones that have been through the tumbling process but did not pass our quality test. They work great as media and another trip through the process will improve their quality.
Ceramic media and plastic pellet 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.

What Is Rock Tumbling Media?



Rock tumbling media is a rounded or cylindrical material added to the tumbler barrel to improve the results of your tumbling. It improves the tumbling action, facilitates abrasion on all surfaces of the stones, and helps to prevent chipped and bruised tumbled stones.

Most media used today is a kiln-fired ceramic that has a hardness of 7+ on the Mohs scale and an excellent tenacity. It is extremely durable, reusable, easy to clean, and will last through many batches of tumbled stones. We use ceramic media in all of our rotary and vibratory tumbling.

Plastic pellets were the most popular tumbling media of the past. They were used to cushion the stones and reduce bruising caused during tumbling. Today most people use ceramic media, but some have used plastic pellets for decades and still prefer them for rotary tumbling. (Plastic pellets are not suitable for vibratory tumblers). Ceramic cylinders can cushion just as well as plastic pellets. They are also hard and more effective at grinding and shaping stones.


Benefits of Using Ceramic Media:



When properly used, ceramic tumbling media can improve your tumbled stones. Here are several benefits from using ceramic cylinder media:

1) Cushioning: To absorb impact energy between the stones in the barrel.

2) Particle Size Balancing: Add small particles to a load of large rocks.

3) Filler: Get the barrel up to operating capacity.

4) Improve Tumbling Action: Make the rocks in the barrel tumble better.

5) Deliver Grit to All Rock Surfaces: Facilitates polishing and grinding.

Now that you understand the benefits of using ceramic tumbling media you still need to determine... Which size should you use? How much should you use? Below are recommendations on how you can achieve the benefits listed above.
Quartz tumbled with and without cushioning
The two photos above are of the same piece of rock crystal.

The top image shows the piece after being tumbled without proper cushioning. The stone has numerous chips and bruises. This damage was cause by hard impacts with other stones in the barrel.

The bottom image shows it after being re-tumbled using ceramic media as cushioning. You can see how much less chipping and bruising are on the stone.

Cushioning:



Have you ever tumbled a batch of rough only to open the barrel after the polishing step and notice little white fractures or chipping around the edges of your stones? It is called bruising and it happens when the stones hit against each other with enough force to cause damage. Cushioning your stones will reduce, and in many cases, eliminate this problem.

How does media provide cushioning and stop your stones from bruising each other? Media in the barrel will keep the stones from hitting one another as often as they do when there is no media. The media will also slow down the stones and reduce the force they have on each other when they do come together.

Think of a child jumping into a ball pit. If there were no balls in the pit the child would have a high energy impact with the floor. However, with the balls in the pit there is no high energy impact. The initial energy from his fall starts to be absorbed by the first balls his body touches. That energy is then transferred with less force to all of the balls that they touch. Then with even less force the energy is transferred to all of the balls that they touch. This continues until all of the energy has been absorbed through less and less forceful impacts between the balls. This energy absorption keeps the child from hitting the floor or if they do hit the floor it is with very little force. Using ceramic media in the barrel can have the same effect on the rocks in the barrel.

Two types of materials require cushioning: 1) those that bruise or chip easily; and, 2) those that break easily by cleavage.

Materials that bruise or chip easily include: obsidian, glass and crystalline quartz. (Banded amethyst, rose quartz, rock crystal, aventurine, and tiger's eye are common varieties of crystalline quartz.) These materials can be chipped or bruised by impacting with one another in the barrel. Adding media for cushioning can reduce this damage.

Materials that cleave easily include: fluorite, topaz, moonstone, amazonite, labradorite and orthoclase. Many people avoid tumbling these materials because they are difficult to tumble with good results. Adding media for cushioning can solve that problem.

We use at least 50% media in the barrel to properly cushion fragile tumbling rough. Small ceramic media works best to cushion the material. We usually use a mix of large and small media for cushioning because it also helps with particle size balancing.
Particle size balancing with ceramic media
The top illustration shows how much empty space there can be in a barrel of large rough. It also shows there are not many contact points between the rough. Grinding and smoothing occurs when grit is caught between these points of contact. If you increase the number of contact points, more smoothing and grinding will occur.

The bottom illustration shows how media can fill the spaces between the stones. Filling in those spaces also creates many more contact points on the rough. The stones in the bottom illustration will shape much faster and are less likely to chip or bruise.

Particle Size Balancing:



What is particle size balancing? Particle size balancing is making sure that you have a range of different sized material in the barrel. If the rough in the barrel are all large pieces there won't be many points of rock to rock contact as they tumble. Grit does its job when it is caught between the stones and the media. The pressure of that contact enables the particles of grit to abrade and smooth the stones.

Imagine bowling balls in a box, there are only a few points where they touch each other. Now if you put some golf balls in that box you have significantly increased the number of contact points on the bowling balls and filled much of the empty space between them. Adding marbles would fill in even more of the empty spaces in the box and maximize the points of contact against the bowling balls. This shows how using a range of particle sizes in the barrel increases the number of contact points where the shaping and smoothing of the stone occurs.

The best way to get a balanced load in the barrel is by using a range of smaller pieces of rough. If you don't have smaller pieces of rough ceramic media should be used. If you are using ceramic media for the first time we suggest getting both small and large because having a range of sizes in the barrel works best.


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 ceramic cylinders will help 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. A mix of ceramic media sizes works best.

Filler:

Large ceramic tumbling media
Unused large ceramic media ready to be used as filler. Notice how it has sharp edges. Do not use band new media in the fine and polish steps. The sharp edges will scratch your stones. We introduce new media in the coarse grit or medium grit step and then it is ready when the fine grit and polishing steps arrive.


The most important use of ceramic media as filler is in replacing the volume of rock lost during the coarse and medium grit steps of the tumbling process.

During the coarse grit step between 10% and 30% of the rock volume in your barrel is lost to grinding. It is worn away and becomes the rock mud that you see in the barrel after tumbling a batch of rocks.

To maintain a good tumbling action and to keep your barrel up to the recommended tumbling volume of about 2/3 full, adding ceramic media is recommended. We add enough ceramic media to bring the barrel up to about 2/3 full.

Less rock volume is lost during the medium grit step, but it is still important to add ceramic media to keep your barrel at the recommended tumbling level.

Replacement of rock volume with ceramic media is important in both rotary and vibratory tumblers. The ceramic media helps give your rocks a smoother ride during the fine grit and polishing steps. Without the addition of media, the rocks will receive a rougher ride that might cause chipping and bruising.

Magnesite after coarse grit
The photo above shows what happens to rough during the coarse grit step using different amounts of media. The two stones on top were tumbled for one week in a barrel that contained a little over 50% ceramic media. The stones on the bottom were tumbled in a barrel with all similar size rough and no media for one week. Notice the stones on the bottom are more rounded.
(In the past, we used to recommend the use of ceramic media during the coarse grit step of rotary tumbling if you did not have enough rough to fill the barrel up to its recommended operating capacity. We have found through testing that better-shaped stones are produced during the coarse grit step in a rotary tumbler when only about 10% of the load (by volume) is ceramic media. Too much media can prevent the stones from aggressively wearing away the points and edges of one another.

The only situations where we would use more than about 10% media during the coarse grit step of rotary tumbling are: (A) when we have a barrel full of large material with nothing filling the spaces between the rocks, then we might use up to about 20% media to improve the tumbling action; and, (B) when the rocks already have a nicely rounded shape and only surface smoothing is needed.)
Our media bucket
Here is a look into our media bucket. You can see a range of ceramic media sizes in the bucket as well as some small stones that have already been tumbled at least once. We scoop out of this bucket every time we start a new batch of stones.

How Long Will Ceramic Media Last?



Ceramic tumbler media has a hardness of about 7+. It is harder than almost all of the most commonly tumbled rocks such as agate and jasper. Small media will last a few tumbling cycles when used in all steps of the tumbling process. Large ceramic media will last much longer and eventually turn into small media.


How Do We Use Media?



We use between 10% and 50% ceramic cylinder media every time we run a tumbler. We believe that a mix of large and small media works best. Tiny tumbled stones also enter into our media plan.

After each batch of rocks is tumbled, we separate media from tumbled stones using a classifier. The tumbled stones do not pass through the classifier, but all media and a small number of tiny tumbled stones fall through into Our Media Bucket. This bucket always contains polished media in a range of sizes ready for use in tumbling. We keep it supplied by frequently adding a small amount of new large media to the coarse grit step of each batch of rocks that we tumble.

If you do a lot of tumbling or simply want to save time, we suggest that you read Our Media Bucket article.
Plastic pellets
Plastic pellets are most often used to cushion stones during the fine grit and polish steps of the tumbling process.

Plastic Pellets:



Plastic pellets have a long history of use for cushioning in rotary tumblers and many people still use them. They are not recommended for use in vibratory tumblers.

We stopped using plastic pellets years ago after we tried ceramic media. We found that ceramic media are just as effective as plastic for cushioning. Here are a few other reasons why we switched to ceramic media for all of our tumbling.

Plastic pellets...
1) Are difficult to separate and gather after rinsing.
2) Are tough to get clean and dry before storing.
3) Cannot be reused in a finer grit stage because grit can imbed in them and contaminate the next steps.
4) Must be stored in separate containers according to the grit they were used in.
5) Do not help much with grinding because they are soft.


Not All Ceramic Media Works in Rock Tumbling



Ceramic media is sold for a wide variety of purposes and most of it has embedded abrasive granules. If you use ceramic media with embedded abrasive granules during the polish step they will scratch the stones and ruin your polish. All of the ceramic media that we sell is smooth and does not contain any abrasives.

Happy Tumbling!

Article Authored by



Brad Cole Bradley Cole: Bradley is the manager of RockTumbler.com and has authored much of the content on this website. He also does customer support, photography, maintains the website, and consults with customers about rock tumbler repair and maintenance.
Hobart King Hobart M. King: Hobart is the owner of RockTumbler.com and has authored much of the content on this website. He has a PhD in geology and is a GIA graduate gemologist. He also writes most of the content for Geology.com.