Home » Rock Tumblers
Machines that reveal the hidden beauty of rocks and minerals.
Rock Tumbler Kit: Most small rock tumblers are sold as a kit that includes: the tumbler machine, a tumbler barrel, instructions, crushed rock, abrasive grit, and polish. The tumbler shown in the photo above is a Thumler's MP-1 that is sold with a small rubber barrel. Rubber barrels are highly recommended over plastic barrels because they last longer and make a lot less noise.
What is a Rock Tumbler?
Rock tumblers are machines used to smooth and polish rocks. They are a popular tool used by jewelry, craft, and lapidary hobbyists for producing tumbled stones. Rock tumbling is also popular with people who want to discover the hidden beauty of rocks and minerals. Starting with a rough piece of rock and tumbling it into a beautiful, jewelry-quality stone is a very rewarding experience.
Tumble-Polished Stones: Some examples of nice tumbled stones. Visible in this image are fancy jasper, tiger's-eye, carnelian agate, sodalite, banded agate, tree agate, banded amethyst, eye agate, zebra jasper, blue lace agate, blue chalcedony and more.
How Do Rock Tumblers Work?
The most popular tumblers have a barrel that is loaded with rocks, water, and abrasive grit. The abrasive grit is a granular material similar to the grains glued onto sandpaper. The grit is often labeled "coarse," "medium," and "fine," similar to the different grades of sandpaper.
The barrel containing rocks, grit, and water is placed on a motorized machine that rotates the barrel to tumble the rocks that are inside. As the rocks tumble, they grind against one another with particles of the abrasive grit caught between them. This action wears sharp edges off of the rocks and smoothes their surfaces. Tumblers that operate this way are known as "rotary tumblers."
The rocks are typically tumbled for one or two weeks in coarse grit, one week in medium grit, and one week in fine grit, with a thorough cleaning of the rocks and the barrel between each grit size. Then the rocks are tumbled for one final week with water and a rock polish. After following this procedure, the rocks are usually transformed into brightly polished stones.
Toy Tumbler: The tumbler above is a toy tumbler with a small plastic barrel. This type of tumbler has a low price and will usually last long enough to produce a couple batches of stones. The plastic barrel will wear out quickly, and the tumbling stones inside will make a lot of noise.
Types and Sizes of Rotary Tumblers
Rock tumblers are made in a wide range of sizes for different types of use. The three basic categories are described below.
TOY ROCK TUMBLERS
The smallest and least expensive tumblers are toy tumblers with a plastic body and barrel. These machines typically sell for between $40 and $80 online or in local toy and craft stores. The advantage of these machines is their low price. However, they only tumble a few ounces of very small rocks, they have a very short life before they wear out, and the rocks tumbling in the plastic barrel make a lot of noise - noise is a very common complaint about toy rock tumblers.
Hobbyist Rock Tumbler: The tumbler shown above is a Thumler's Model B rock tumbler. It is one of the larger and best hobbyist-grade tumblers. It has a metal barrel with a rubber liner that is large enough to process about ten pounds of rock. Model B tumblers have been manufactured by the Tru-Square Metal Products Company since the 1960s and many of those early tumblers are still in reliable use today.
HOBBYIST ROCK TUMBLERS
Hobbyist tumblers typically sell for between $70 and $300, depending mainly upon their size. Most are made with a metal frame and a quality motor designed to operate for years. They operate quietly because they have a rubber barrel or a metal barrel lined with rubber. They typically tumble between two and ten pounds of rock.
Hobbyist tumblers were first made in the late 1950s. Two brands, Thumler's Tumblers and Lortone, are still being manufactured today with very little change to their basic design. Successful products persist in the marketplace. Many people received a hobbyist tumbler by Thumler's or Lortone as a gift when they were a child and are now using that same tumbler with their grandchildren!
Instead of being made with plastic, hobbyist tumblers are made from metal and other durable materials. Thumler's and Lortone parts are still manufactured today. Most of their tumblers can be repaired or refurbished with readily available parts.
Commercial Rock Tumbler: The machines above are commercial tumblers operated by TOPSTONES. These tumblers are used to tumble several thousand pounds of tumbled stones in a single batch. Image used with permission of TopStones.
COMMERCIAL ROCK TUMBLERS
Commercial tumblers are large machines that can tumble a few dozen to a few thousand pounds of rock at a time. They cost several hundred to many thousands of dollars and are used almost exclusively by people and companies who are in the business of producing tumbled stones.
Rocks: Before and After Tumbling: This photo shows rocks before and after tumbling. The rocks on the left are crushed pieces of (from top to bottom) brown jasper, rose quartz, green aventurine, amethyst, and tiger's-eye. The rocks on the right are the same types of rocks after tumbling. Notice how the stones after tumbling are slightly smaller, have rounded shapes and a bright polish.
What Types of Rock Can Be Tumbled?
Most rocks will not perform well in a rock tumbler; however, a few types of rock can be successfully tumbled by a beginner if the rocks are carefully selected. These easy-to-tumble rocks include agate, jasper, chalcedony, and petrified wood. All of these materials are composed of microcrystalline quartz, which is a very hard, tough, and durable material that accepts a very bright polish.
Rocks that are worth tumbling are free of voids, cavities, and fractures. They also have a non-granular texture. Many people are lucky enough to live in a location where these rocks can be collected, always with permission of the landowner, in streams or beaches or scattered on the surface of the ground. If you do not live in one of these locations, then good material for tumbling can easily be purchased at a rock shop or from a website that sells rock tumblers and rock tumbling supplies.
Many other types of rocks and minerals can be tumbled in a rock tumbler. A partial list includes: Amazonite, Amethyst, Aventurine, Basalt, Beryl, Bloodstone, Carnelian, Chrysoprase, Flint, Fluorite, Granite, Hematite, Labradorite, Lapis Lazuli, Malachite, Obsidian, Petrified Wood, Rhodochrosite, Rhodonite, Rose Quartz, Smoky Quartz, Sodalite, Sunstone, Tiger's-Eye, Turquoise, Unakite, and many others.
Rock Tumbler Crafts: A small sample of the many things that you can make with tumbled stones produced in your rock tumbler. Your imagination is your only limitation!
Your Kids Want a Rock Tumbler?
Rock tumbling is a great family activity - and that's the way the hobby should be done.
Children under age 14 require adult help and supervision. They will need help following the instructions, help opening tumbler barrels with small hands, and 100% supervision because a rock tumbler has a motor that is powered by electricity. An adult might also be needed to clean up an accidental spill.
Each step in the rock tumbling process takes about seven days. So many parents, grandparents or other supervising adults often set aside a special time of the week - like Saturday morning - to tend to their rock tumbler. After you, the adult, know what you are doing, changing a rock tumbler from one step to another will take less than an hour (more if your kids want to ogle their rocks - and most of them will want to ogle their rocks every week - it's part of the fun of rock tumbling). Plan for a couple hours the first time and be ready to enjoy learning about rocks together.
The schedule of rock tumbling is very flexible. If you can't tend to your tumbler on Saturday morning, Friday night will work fine and Sunday evening will work fine too. Allowing your tumbler to run for six to eight days (or a little longer) will not hurt a thing. It is better to allow the rocks to tumble a little longer than it is to cut the process short. Cutting the process short will prevent the rocks from being adequately shaped and smoothed for the next step in the process.
One thing that you should not do is stop the rock tumbler and allow the barrel and its contents to go uncleaned between steps. If you stop the tumbler and don't clean the rocks promptly, the mud in the barrel will start to harden. So, if you can't change the tumbler Saturday morning and plan to change it on Sunday evening, just allow it to continue running.
For more information about polishing rocks in a tumbler, visit the rock tumbling library on RockTumbler.com.
Tumbled Stone Crafts and Gifts
Most rock tumbler kits are supplied with a small jewelry kit that you can use to make a couple gift items from your first batch of tumbled stones. Keychains, pendant necklaces and other small jewelry items make great gifts.
Tumbled stones can also be used for many other things. They can be used as accents or ground cover in potted plants, glued around the edges of picture frames, used as game pieces, dressed up with eyes and antennae to make rock critters, used as vase fillers, placed in a bowl and used as a cosmetic brush holder. The accompanying images show a few of the things you can do with tumbled stones.
Find Other Topics on Geology.com:
Rock tumbling is a relaxing and rewarding hobby for people of all ages. My daughter and I enjoy tumbling batches of rocks together and she particularly enjoys finding creative ways to use the exceptionally beautiful rocks that are produced as the end result. If you’re interested in getting into the hobby of rock tumbling yourself but aren’t sure where to begin, you’ve come to the right place.
As a professional geologist, I know quite a bit about rocks in general, but I had never tumbled rocks before I got into the hobby with my daughter. I have learned a lot about the process and how to produce the best results and I wanted to share that knowledge. Here is a complete guide to rock tumbling, with everything you need to know from start to finish.
Acquire a Rock Tumbler & Supplies
If you want to get into rock tumbling, the very first thing you’ll need to do is get your hands on a rock tumbler. Rock tumbling as a hobby isn’t particularly expensive, but your first rock tumbler will definitely be the biggest investment you’ll have to make.
You’ll want to consider the size, quality, type, and price of your first tumbler to make sure you get the right one for your situation. If you’re looking for a great rock tumbler to get started with the hobby then I’ll point you towards my ‘recommended rock tumbler‘ article where I detail everything I love about National Geographic’s 3 lb Rock Tumbler (link to Amazon).
What Size Tumbler To Get
Tumbler size is defined by the size of the barrel you put the rocks in. They are usually described in terms of pounds of rocks that the barrel can fit. Many beginners are tempted to get the cheapest, smallest tumbler available. These tend to be 2-pound barrels or less, are geared more towards kids, and are really more of a toy than a serious rock tumbler. In my opinion, these are a waste of money and should be avoided, even by casual beginners.
I would suggest that most people start out with a 3-pound tumbler. This is large enough to tumble a decent amount of rocks and anything that comes in this size or above will be more likely to be of a higher quality. Make sure that the barrel of your tumbler is made of high-quality rubber and not plastic. Plastic will be much louder and will drive you crazy with the amount of noise it makes.
You can purchase tumblers with barrels much larger than three pounds, but I wouldn’t advise this for beginners. The same goes for tumblers with more than one barrel. Invest in a decent quality 3-pound single barrel tumbler, and if you go through a few tumbles and want to upgrade to something bigger or fancier then go ahead.
Rotary or Vibratory Tumbler?
As you’re looking around for tumblers you may notice that some are described as ‘rotary’ while others are ‘vibratory’. When most people think of rock tumblers they picture a rotary tumbler, which is definitely what I’d recommend a beginner start out with.
Vibratory tumblers are great because they take much less time to produce results, but they are also more expensive and quite a bit louder than rotary tumblers. They are also typically used in conjunction with rotary tumblers, not as a complete replacement.
Rotary tumblers work by turning the rocks over in a barrel, causing the rocks and grit to rub against each another. Vibratory tumblers work by rapidly shaking a bowl which causes the rocks to flow over one another. If you’d like to know more about the differences and which type is right for you, I wrote an entire article comparing rotary and vibratory tumblers.
A good tumbler isn’t the only piece of equipment you’ll need. In order to get good tumbling action in your barrel, it needs to be filled up around 3/4 of the way full with rocks. During the tumbling process your rocks will gradually get smaller and smaller as they get worn down. This means that for each tumbling step, the volume of the rocks in the barrel will decrease. That’s where tumbling media comes in.
In order to replace the lost volume of the ground up rocks you can use tumbling media. For example, if your barrel started at 3/4 of the way full in the first tumbling step but by step 3 it’s down to half, you can fill your barrel up with tumbling media to make it 3/4 of the way full again. This keeps your rocks tumbling well in the barrel and prevents them from getting ‘bruised’ (more on that later).
The most popular types of tumbling media are ceramic pellets and plastic pellets. If you are using a vibratory tumbler then only ceramic pellets are recommended, but if you’re using a traditional rotary tumbler you can use either. I prefer using ceramic media because I find it contributes more to the smoothing process. It’s even better if you get varying sizes of ceramic media, but that is far from necessary.
If you want to check out my reviews of all thee tumbling media and grit I use I’ll point you to my recommended gear page. The ceramic media that I myself have used can be found here on Amazon. If you’d prefer to use plastic pellets as your media I’d suggest these from Amazon.
The last essential item you’ll need is tumbling grit. This is the stuff that does all the grinding and polishing – the secret sauce. It’s tiny little particles of very hard material that your pour into the tumbler. While the barrel turns, the rocks get coated in with the grit and it rubs on their surface, slowly grinding and polishing the rocks until they are nice and smooth.
You’ll need at least four different sizes of grit – one for each tumbling step. You can buy them in pre-measured sets for one tumble, or buy the grit for each step in bulk. For your first tumble, I would recommend buying a pre-measured set of grit. Once you get a feel for things you can buy more grit in larger quantities if you’d like.
Most tumblers that you buy will probably come with grit for your first tumble, but if you bought yours used or it didn’t come with any I would personally recommend that you buy this set of grit from Amazon.
There are some other items that are very helpful but not necessary for the tumbling process. These will make your life easier and might help you get better results.
The first is a child’s toothbrush with a short handle, preferably one with soft bristles. You can use this in between tumbling stages to clean the grit out of the tumbling barrel and to thoroughly clean off your rocks. The short handle is important because you won’t be able to get the toothbrush into the barrel at the proper angle if it has a longer handle.
The next is a designated colander for rinsing off your rocks. You can use one from your kitchen but I know my wife would frown on using the same one we use for cooking. I’d also recommend using a plastic one because it won’t scratch your rocks – a metal one might scratch up your fresh, shiny rocks before you even get to enjoy them.
Gather Rocks to Tumble
Of course, you’re going to need some rocks to tumble! This is where the real fun begins. Not every type of rock is suitable for tumbling (in fact, most aren’t), but there are still plenty of unique and amazing rock types to choose from. If you’re looking for inspiration, I wrote an entire article on the best kinds of rocks to tumble.
What Type Rocks to Tumble
Good tumbling rocks will be hard, dense, and relatively smooth. Most of the best rocks to tumble will be between a 6 and an 8 on the Mohs hardness scale. This harness range contains all of the many varieties of quartz including agate and jasper.
It’s also important not to mix softer rocks with harder ones. The harder rocks will ‘eat’ your softer ones by gradually grinding them completely away. Depending on how long you plan to tumble your rocks and how big they are, I would suggest trying to keep their relative hardness within a range of about 1.5 on the Mohs hardness scale.
Here are some of the best rocks I’ve found for tumbling. If you want to know more about each of them please see the article I posted above (or click here).
|Quartz||7||White to clear|
|Agate||6.5-7||Varied: banded brown, white, pink, yellow, red|
|Jasper||6.5-7||Varied: brown, yellow, red, orange, green|
|Sodalite||5.5-6||Most commonly blue with white veins|
|Rose Quartz||7||Light Pink|
|Amethyst||7||Varying shades of purple & violet|
|Tiger’s Eye||7||Golden to red-brown, banded/fibrous|
|Aventurine||6.5-7||Most commonly seafoam green|
Inspect Your Rough
Before you begin the tumbling process make sure to do a visual and tactile inspection of each of your rocks. You want to make sure that each rock is suitable for tumbling, because even one sub-par rock can negatively impact (or even totally ruin) all of the other rocks in the barrel.
Things to check before tumbling your rocks:
- Make sure all rocks are of similar hardness – Softer rocks will get completely worn away and destroyed by harder rocks.
- Discard any rocks with obvious fractures or cracks – Break cracked rocks in two along their fractures if you want to include them in the batch. If a rock breaks mid-tumble the sharp edges will damage other rocks in the barrel.
- Remove rocks with pores or cavities – Small cavities on the surface of a rock will trap grit and bring larger sized grit to the next tumbling steps, resulting in a hazy and undesirable final product.
- Use a good distribution of rock sizes – Differently sized rocks tumble more smoothly and evenly, and result in more points of contact between the rocks and better grinding action. Use ceramic tumbling media as a substitute if you only have large rocks.
Where to Find Rocks
Many people prefer to tumble rocks that they collect themselves. This can be a lot of fun and very rewarding, but is also time consuming and not everyone has access to places with rocks suitable for tumbling. Try scouring locations known for rocks like agate, jasper, and other varieties of quartz. If you’d like to find your own rocks but aren’t sure how to start I’d recommend checking out my article on the subject.
Where to Buy Rocks
There are plenty of places to buy tumbling rough (un-tumbled rocks) online. You can buy differently sized batches and all different kinds of rocks. Some people prefer to tumble entire batches of a single type of rock, while others enjoy tumbling an assortment of rocks.
For beginners, I would recommend this 3-pound assortment of rocks from Amazon. It has a really nice mix of jasper, agate, quartz, and other rocks in an assortment of sizes for really nice tumbling action at a reasonable price.
Tumble Rocks with Coarse Grit
Now we can really get down to business. Time to start tumbling! The tumbling process is almost always done in four steps. Each step uses progressively finer and finer grit like you’d do with sandpaper when smoothing a piece of wood. The first step in rock tumbling is done with coarse grit.
Purpose of Coarse Grit Step
The coarse grit step (usually referred to by hobbyists as ‘Step 1’) is very important because it’s where your rocks really take their shape. If you want your rocks to be well rounded with few bumps or irregular shapes then you want to take special care with this step. Once your rocks move beyond step 1 they won’t change shape much. It is worth leaving your rocks tumbling a little longer in order to achieve the rounded shapes you desire.
|Purpose of Step||Grit Size||Grit Amount||Tumbling Time|
|Shape & round the rocks||60/90 silicon carbide||2 Tbsp / pound of rock||10-14 days|
Loading the Barrel
Open up the barrel of your tumbler and make sure it’s clean. Rinse it out with water and make sure there is no lingering dust or debris. Also rinse your rocks off (either by hand or in a colander) and then place them into the barrel.
The barrel should be at least 2/3 of the way full, but ideally closer to 3/4 of the way full. If it’s not full enough then top it off with some of your tumbling media. This is essential to get the proper tumbling action. If it’s not full enough the rocks will fall irregularly and with too much force, potentially causing them to break. Conversely, if it’s too full the rocks will be too jammed in there to move as necessary.
After loading your rocks, it’s time to add the tumbling grit. For most rocks, the coarse grit will be 60/90 grit silicon carbide. You want to add about two level tablespoons of grit for every pound of rock. If you’re using two pounds of rock, then use four level tablespoons of grit. Note that that this doesn’t refer to the size of your barrel – it is the actual weight of the rocks you’re tumbling. The amount isn’t an exact science so don’t fret over exact measurements.
After adding the grit, all that remains is the water. Fill the barrel up so that the water just barely covers the top of the rocks – don’t fill it to the brim. If you have especially hard tap water you might consider using distilled water, but it’s far from necessary.
Now that your barrel is filled it’s time to seal it up. Each model of tumbler barrel is a little different by the concept is the same – you just want to ensure that the seal is tight and completely waterproof. Check for any stray grit or bits of rock along the edges before sealing it up, otherwise the seal will gradually degrade and eventually you’ll end up with a big mess on your hands.
How Long to Tumble
For step 1 of the tumbling process, most rocks should be tumbled between 10 and 14 days. This stage takes longer than the others because it’s where the vast majority of the rounding and shaping occurs. If for some reason you’re concerned about tumbling your rocks too long you can stop the tumbler at 10 days and open it up and spot check your rocks. If they are well-rounded enough for you then you can stop there, but otherwise, let them go for a few more days.
Some tumblers have multiple speed settings. If this is the case for you then I’d recommend setting the speed towards the higher end of the spectrum for this step. This will make the rocks round more quickly, but more importantly it will increase the chances of breaking rocks before they get to a later step. If your rocks have weak spots that will potentially cause them to break it’s best to get it out of the way early so that those sharp edges have a chance to smooth out.
Clean Rocks After Tumbling
Once your rocks are done tumbling it’s time to clean them off and prepare them for the next tumbling step. If possible, take your barrel outside next to a hose. If not, you’ll need a 5 gallon bucket to trap the slurry. DO NOT PUT THE SLURRY DOWN A DRAIN. It will clog your pipes and you’ll have a very bad time.
Do NOT put the slurry down a drain.
Carefully open up your tumbler barrel, making sure not to splash the contents everywhere. Then take a colander (preferably a designated plastic one as I discussed earlier), hold it over the grass or your 5 gallon bucket, and pour the contents of the barrel into it. It will trap the rocks and any tumbling media you used, allowing the slurry to drain through.
Next, thoroughly rinse the rocks with your hose or a pitcher of water, etc. Give the colander a few shakes and really try to remove as much of the slurry as possible from the surface of the rocks. Then, if you tumbled the rocks with any tumbling media, pick the rocks out and place them somewhere clean. You can save the media in a container (I just use a plastic bag) to be used in step 1 of another batch.
At this point, I like to wash each of my rocks individually using a toothbrush to make sure they are completely devoid of any lingering grit or slurry. At the very least, look your rocks over again and make sure there are no fresh cracks that could be hiding grit or cause the rocks to split in the ensuing steps. Even a few missed grains of coarse grit can cause your rocks to come out hazy and dull if they get moved to the next steps, so make sure each rock is very clean.
Prepare Barrel for Next Step
Just like you did with the rocks, now you need to make sure the tumbling barrel is super clean. Rinse it out really well with warm water and that should take care of the vast majority of the slurry, and do the same with the lid. Then take your short-handled toothbrush and really scrub the corners/edges of the barrel where slurry tends to stick and accumulate.
Keep rinsing and scrubbing until everything is gone, then give it a good wipe-down with a paper towel. Then rinse it with warm water again. At this point, you’re probably good to go. It should look just like new when you’re done. All this effort will give you better results in the end and it will also extend the life of your tumbler.
Continue Tumbling Rocks with Medium Grit
Now it’s time to move on to the medium grit phase of the tumbling process, typically referred to as ‘Step 2’. In most respects, this will be very similar to the previous step.
|Purpose of Step||Grit Size||Grit Amount||Tumbling Time|
|Finish shaping, begin polish||150/220 silicon carbide||2 Tbsp / pound of rock||~7 to 10 days|
Purpose of Medium Grit Step
This step will continue to shape the rocks, although to a much lesser extent than the coarse grit stage. At this point, the rocks are pretty much in the general shape that they will stay in for the remainder of the process and we’re just smoothing them out. The medium grit step does the bulk of the work smoothing the surface of the stones, preparing them for pre-polishing and polishing.
Loading the Barrel
You’ll now load the tumbler barrel pretty much the same way you did in the last step. Everything should be nice and clean already, so just place your rocks in the barrel.
At this point, you’ll want to take note of how high full the barrel is because each rock will be significantly smaller than it was before the tumbling process began. If the barrel is less than 2/3 of the way full, add some tumbling media to get it up to 2/3 or 3/4 of the way full.
Next, add your grit. For this stage you’ll probably want to use 150/220 silicon carbide. The amount will be the same as in Step 1, which is 2 tablespoons per pound of rock. (Note that you should include the media in this weight calculation.) If you’re using a 3 pound tumbler then you’ll be safe using 4 tablespoons of grit.
After that, add your water. Fill the tumbler up so that the water almost covers the top of the rocks, leaving about 1/8 of an inch of the rocks exposed above the surface. All of these ingredients together will mix up and for a nice slurry.
How Long to Tumble
The amount of time to tumble your rocks will vary with their hardness, but for the vast majority of popular tumbling rocks you should put them in for about 7 days. For slightly harder rocks or rocks that still need a little more shaping you might want to leave them in for up to 10 days. If your tumbler has multiple speeds then choose a slow setting for this step.
If you are tumbling rocks on the softer side (with a hardness of 5 or lower) then you will likely want to adjust the time spent on this step to 4 or 5 days, checking on them every couple of days. You don’t want your rocks to be completely eaten up by spending too much time in the tumbler.
Clean Rocks & Barrel After Tumbling
Once the rocks have tumbled long enough, stop the tumbler and clean your rocks and barrel in exactly the same way as you did in Step 1. Make sure you don’t rush the process. Get every little drop of slurry and bit of grit off of the rocks and out of the tumbling barrel, and don’t forget: do not pour the slurry down your drain.
Tumbling Rocks with Pre-Polish / Fine Grit
The next step is usually referred to as ‘Step 3’ and it’s where your rocks will really start polishing up. The grit you’ll use is very small, and is sometimes called ‘pre-polish’. The procedures in the step will be almost identical to those of the medium grit phase (Step 2).
|Purpose of Step||Grit Size||Grit Amount||Tumbling Time|
|Continue Polishing||500 silicon carbide||2 Tbsp / pound of rock||~7 days|
Purpose of Fine Grit Step
In this step, there will be virtually no re-shaping or additional rounding of your rocks. The shape they enter in will be pretty much their final shape. This step is where your rocks will start really polishing up. When they’re done in the fine grit they will really begin to shine and some may even start displaying some luster.
Loading the Barrel
You’ll load the barrel just like you did in the previous step, the only difference being the type of grit you use. Load up your clean rocks, add about 2 tablespoons of grit per pound of rock (about 4 tablespoons if you’re using a 3-pound tumbler), and add enough water to almost cover the top of the rocks. As always, make sure the seal of your barrel lid is extremely clean so that it doesn’t degrade or lead to leaks.
How Long to Tumble
This step should take about 7 days for most types of rocks, including just about every type of rock that a beginner will be working with. I wouldn’t leave any rocks in this step for any longer than that unless you’re tumbling something unusually hard like a form of corundum. If you are polishing softer rocks then 4 or 5 days will probably be sufficient.
Clean Rocks & Barrel After Tumbling
Just as you’ve done in the previous tumbling steps, thoroughly clean off your rocks using the colander and a soft brush. At this stage I think it’s especially important to use a plastic colander – a metal one will scratch up your rocks which would be disastrous. Clean out your barrel with even more care than usual this time, because any leftover grit will potentially ruin the last and most important polishing step.
Finish Tumbling Rocks with Polishing Grit
This step is probably the most important one, and in my opinion is also the most exciting. You’ll want to take extra care with this step because this is where they’ll develop the nice shine and luster that every tumbling enthusiast is after.
|Purpose of Step||Grit Size||Grit Amount||Tumbling Time|
|Finish polishing||Aluminum Oxide Powder||2+ Tbsp / pound of rock||~7 days|
Purpose of Polishing Step
We’ll be using extremely fine grit on this step that will polish your rocks to a nice smooth shine. This phase is usually referred to as ‘Step 4’ in most instructions. If you’re done everything correctly up to this point they should be looking good already, but the polishing step will really make them pop.
Loading the Barrel
The barrel loading process will be pretty much the same as previous steps, but with some possible slight variations. Some people that have been tumbling for a long time have a dedication barrel that they use only for the polishing step, the idea being that you can avoid possible contamination of larger grit sizes from previous steps. This certainly isn’t necessary, but if you do happen to have two barrels then it’s not a bad idea.
Your barrel and rocks should be clean already, but take this time to double check everything. Even a few pieces of larger grit or a stray drop of slurry can pretty much ruin a polish step, wasting your time and money.
Put your rocks in the barrel, and top it off with as much ceramic or plastic media as needed to make the barrel 3/4 of the way full. Then, put in the aluminum oxide polishing powder. This stuff is extremely fine, so take care not to pour it too quickly or it’ll puff all over the place. Use the same amount as in previous steps (~2 tablespoons per pound of rock), with maybe an extra tablespoon if you’re feeling generous.
Fill the barrel with water almost to the top of the rocks, just as you did in the previous two steps. Then seal up the barrel with the lid, once again checking to make sure the seal is extremely tight and there is no grit or debris getting in the way.
How Long to Tumble
Most rocks will polish very well in about 7 days. I like to let them go for about a week, then open up the barrel and spot check them. If they look the nice, polished, finished product I’m looking for them I’ll end it there, but if not then just let them go for another day or two.
Clean Rocks After Tumbling
Once your rocks are done tumbling then just clean them off as you’ve in the previous steps. They’re all done… probably. When you’re cleaning them off take note and see if you’re satisfied with the results. If they are super smooth but don’t have that nice mirror shine you were hoping for then you’ll likely want to move on to the burnishing step. If you’re satisfied with the results, then congratulations!
Clean the Barrel Thoroughly
In the excitement of completing your tumbling process and inspecting your finished stones, don’t forget to clean out your tumbling barrel. The slurry will dry in there quickly and become almost like cement, so don’t delay in cleaning the barrel out. Leave it clean enough that you can pull it out and begin your next round of tumbling with ease.
Burnish the Rocks If Necessary
If your rocks were a little disappointing at the end of the polishing process, don’t fret just yet. It’s pretty common to have really smooth stones that come out looking a little cloudy or hazy, in which case you will want to add the extra ‘burnishing’ step.
|Purpose of Step||Powder||Grit Amount||Tumbling Time|
|Enhance shine||Ivory Bar Soap Shavings||1 Tbsp / pound of rock||~4 hours|
Luckily, this step is pretty quick and doesn’t cost very much because it doesn’t use specialized grit. You’ll just need a bar of original Ivory bar soap, chopped up into little shavings (use a cheese grater or sharp knife for this).
Load up your rocks and tumbling media and then add about 1 tablespoon of the soap shavings to the barrel. Fill the barrel with water until the water level is just below the top of the rocks, seal the barrel, and let it tumble for about 4 hours. Sometimes this process can really enhance the shine of your rocks, so in my opinion it’s usually worth the time.
There are some tumbling kits out there that come with specialty products for this step. For example, the National Geographic Tumbler that I originally bought came with little cubes of foam they call ‘gem foam’ that are supposed to burnish the rocks. I have never had great success with this kind of stuff, but I also don’t think it hurts.
Use & Enjoy Your Polished Stones
Now that your rocks are done, it’s time to enjoy them! Lots of people like to just keep them in glass jars around their home to put them on display, but there are many fun ways to put your stones to more practical use. My daughter enjoys making little gifts for her friends and family with them.
Some ideas for what to do with tumbled rocks include:
- Make them into refrigerator magnets
- Wire wrap the stones into jewelry
- Use them as game pieces
- Turn them into decorative key chains
- Fill transparent vases
- Use them as paperweights
Rock Tumbler Instructions
Directions for Turning Rough Rocks into Beautiful Tumbled Stones
Working to transform rough rock into beautiful tumbled stones gives most people a great feeling of accomplishment. It doesn't matter how old you are or how many batches of rock you have tumbled in the past - when you finish the last tumbling step, rinse off the polish, and see a super-bright luster on colorful polished stones - you are amazed at what you have done.
Rock Tumbling Is Easy
Using a rock tumbler to convert rough rock into sparkling tumbled stones is easy if you follow a simple procedure and observe a few rules. We are writing this to share the procedure that we have used for many years with a number of rotary tumblers.
This procedure works well with materials that have the following properties:
- an ability to be polished in a rotary tumbler
- a Mohs hardness between 6 and 7
- a size between 3/8" and 1 1/2"
Chalcedony: agate, bloodstone, carnelian, chrysoprase, jasper, chert, flint, and petrified (silicified) wood.
Quartz: amethyst, aventurine, citrine, milky quartz, rock crystal, rose quartz, smoky quartz, tiger's eye.
Rock Types: andesite, basalt, diorite, gabbro, granite, mookaite, novaculite, quartzite, unakite.
The "Golden Rules" of Rock Tumbling
We follow three "Golden Rules" in all aspects of rock tumbling. They are:
- "Garbage in means garbage out"
- "Avoid contamination"
- "Great results take time."
Tumbling will enable you to turn the rough rock on the left side of this photo into the sparkling tumbled stones on the right side of the photo. The results are amazing!
"Garbage in Means Garbage Out"
If you start with garbage (low-quality rough), you should expect low-quality tumbled stones. So, don't hesitate to discard a rock that is porous, fractured, misshapen, or that is not expected to produce an attractive tumbled stone.
You will spend a lot of time and valuable supplies tumbling a batch of rocks. Using quality rough saves time, gives you better value for your money, and produces tumbled stones that are of much higher quality.
We buy lots of tumbling rough from online vendors as part of our hobby and to educate ourselves. We have the best experience buying rough from vendors who: 1) provide clear written descriptions and large clear photos of the rough they are selling, 2) show photos of tumbled stones that they produced themselves from the rock they are selling, and, 3) provide a detailed description of the steps that they followed to tumbled the stones. We have the best experience buying rough from people who are actively involved in rock tumbling.
You will use a different size tumbler grit for each step of the tumbling process. If coarse grit gets into your medium grit step, it will scratch up the rocks and you might need to do the medium grit step over again.
Avoiding this type of contamination is easy: just thoroughly clean the rocks, the tumbler barrel, and your tools when you change from one grit size to another.
Another way that contamination occurs is when you include rocks that are brittle, or have a granular texture. These rocks might break or shed grains in the tumbler. These grains and broken pieces can scratch up every rock in the barrel.
Here is a test that we use to detect rocks that will shed grains in the tumbler. We pick up a piece of rough in each hand. We then rub them together while applying a bit of pressure. If we are easily dislodging grains from the rock, we believe that the rock will likely shed grains during tumbling.
This type of contamination is also easy to avoid. Simply examine your rocks before tumbling, and don't tumble suspect rocks in the same barrel with quality rough. Tumble new types of rough or suspicious materials separately.
"Great Results Take Time"
Don't be in a hurry. Spend time doing a great job. If you tumble a batch of rocks through the coarse grit step and they still have a few rough edges or are not nicely rounded, don't hesitate to run them through the coarse grit step again. Also, spend the time needed to thoroughly clean your work area, tumbler barrel, rocks, and tools between steps to avoid contamination.
"Garbage in means garbage out." The rocks in this photo do not have the potential to become nice tumbled stones. A rock with voids should be thrown away - the voids will trap grit and contaminate your pre-polish and polishing steps. Protrusions can be trimmed off with a rock saw - and that might yield two nicely rounded rocks.
Inspecting Your Rough
Remember the rule "garbage in means garbage out." Practice that by starting with quality rough, and you will have a chance to produce high-quality tumbled stones. We prepare to tumble by examining our rough rock. If we find porous pieces that will not make nice tumbled stones and will carry grit from one step to the next, we discard them.
Rocks that are fractured will break while tumbling and scratch other rocks in the batch. When we see a fractured rock in our rough we discard it or break it along that fracture before it is placed in the barrel.
For best results, your tumbler barrel should be loaded with rocks of mixed sizes (from about 1/4 inch up to about 1 1/2 inches in diameter for a 2-pound or 3-pound capacity barrel). If we need more rocks to fill the barrel to the proper level, we often add rocks that were previously polished but have a rough spot or a blemish that, if ground away, will improve the rock's appearance.
Two final tips before we load the barrel:
1.) Tumbling works best when all of the rocks in the barrel are about the same hardness. If soft rocks are tumbled with harder rocks, the softer rocks will wear away quickly - before the harder rocks are properly shaped and smoothed.
2.) Tumbling works best when all rocks in the barrel are of the same type. If you mix rock types, problems can result - and they will be difficult to diagnose.
When loading the tumbler barrel, you should have pieces of rough with a range of particle sizes. We would mix the above sizes together in the barrel. If you load the barrel with just a few large pieces, there will be very few points of contact between the rocks in the load. Those points of contact are where grit is trapped between the rocks and where grinding occurs. If you have lots of small pieces of rough between the big pieces, there will be many points of contact between the rocks of the load, and the tumbling process will be faster and more effective.
If you don't have small pieces of rock to tumble, you can add small ceramic media to the tumbler barrel. Ceramic media are used as small-size "filler" in tumbling. These tiny cylinders will also act like roller bearings in the barrel and make your load tumble with a smooth action - that smooth action will improve the grinding in the barrel and keep your stones from being bruised. See our video about selecting the right tumbling media.
The Four Step Tumbling Process
Now you are ready to begin what most people call the "Four-Step Tumbling Process." This is described below for a rotary tumbler with a three-pound capacity barrel such as the Thumler's Model A-R1, Thumler's Model A-R2, Lortone Model 3A, or the Lortone Model 33B.
If you are tumbling with the Thumler's Model MP-1 tumbler (which has a two-pound capacity barrel), you can follow the instructions below, but use about two level tablespoons of grit or polish in each of the tumbling steps (Step 1 through Step 4).
Loading the Tumbler Barrel
Before you load the tumbler barrel, be sure that it is perfectly clean. There should be no grit or rock fragments left in the barrel from a previous tumble. To prevent leaks, the rim of the barrel and the lid should be totally free from grit or rock particles.
Once you have a clean barrel, add enough rock to fill the barrel about 2/3 to 3/4 full. With small tumblers it is best to tumble rocks that are between about 1/4" and 1 1/2 inches in size. If you don't have enough rough to fill the barrel at least 2/3 full, the rocks might be tossed around in the tumbler and bruised. (Varieties of quartz bruise very easily.)
It is best to add a variety of rock sizes to the barrel. If you use only large pieces there will be very few contact points between the rocks and very little grinding will occur. If you add a range of rock sizes the small rocks will fill the spaces between the large rocks, creating many more points of contact between the rocks. Grinding occurs when particles of grit get caught between the rocks - so the more points of contact you have the more effective the grinding.
When tumbling you will place enough rocks in the barrel to make it about 2/3 to 3/4 full. Then, add about two level tablespoons of grit for each pound of rock. Finally, add enough water to almost cover the rock. Now seal the barrel and place it on the tumbler.
STEP 1 - Coarse Grind
The first step of the four-step tumbling process is to run the rocks in the tumbler with coarse grit. We begin with a barrel that is about 2/3 to 3/4 full of tumbling rough, then add two level tablespoons of coarse grit (we use 60/90 grit silicon carbide) for each pound of rock. Then, add water until the water line is just below the top of the rocks. Seal the barrel and run for about seven days.
At the end of seven days, open the barrel. You will find a barrel of rocks in very muddy water! Dump the contents into a screen or a colander over a plastic bucket and rinse off every speck of grit and mud. Wear safety glasses to protect your eyes from a splash of mud.
Used grit and rock mud should never be washed down a drain. It can clog your plumbing system. We wash rocks in a plastic colander over a plastic bucket to keep the mud out of the drain.
Inspecting the Rocks:Now that you have washed the rocks, it is time to inspect them. Your goal is to determine if they are ready to move on to STEP 2, or if another week in STEP 1 would improve their appearance. We almost always tumble the rocks for a second week in coarse grit. We believe that improves their shape and removes more blemishes from their surface. Then, we usually move all of the rocks to the medium grit step.
Perfectionist Tumbling:Some people want to have more control over the tumbling process and only admit excellent rocks into STEP 2. These people sort their rocks into three categories:
- 1) those that are ready for STEP 2
- 2) those that could be improved by another week in STEP 1
- 3) those that should be discarded or trimmed and returned to STEP 1
Here are some rocks right out of STEP 1. Note how they are covered with a gray "mud." This mud is spent grit and tiny rock particles that were worn off of the rocks during tumbling. Wash the rocks thoroughly so none of this grit goes into STEP 2. We wash our rocks in a colander over a plastic bucket so none of the mud goes down the drain.
IT IS VERY IMPORTANT TO WASH THE MUD FROM THE ROCKS IMMEDIATELY. If the rock mud is allowed to dry on the rocks it is almost impossible to wash off.
STEP 2 - Medium Grind
The second step of the four-step tumbling process is to run the rocks in the tumbler with medium grit. Before you begin it is extremely important to clean all of the coarse grit and rock mud from the rocks, from the tumbler barrel and from the barrel lid. It is very important to avoid having even a few grains of coarse grit in the medium grind step.
During the STEP 1, your rocks were reduced in size. When you return them to the barrel for STEP 2, they will probably not fill the barrel to the recommended 2/3 to 3/4 full level. If the barrel is only 1/2 full or less the rocks can be tossed violently around in the tumbler. See the accompanying video. This can break or damage fragile materials such as quartz. So, when tumbling quartz or another fragile material we always add enough ceramic media (or some rocks that need a little more tumbling) to bring the barrel up to the 2/3 to 3/4 full level.
(This is less important with varieties of chalcedony because it is more durable material. However, if your tumbler barrel travels at more than about 60 revolutions per minute, we recommend adding enough ceramic media to bring it up to the 3/4 full level reguardless of what type of rock is being tumbled.)
After your barrel is at the proper level, add two level tablespoons of medium grit (we use 110/220 grit or 150/220 grit silicon carbide) for each pound of rock (and ceramic media). Then add water until the water line is just below the top of the rocks. Now tumble for seven days.
At the end of seven days, open the barrel and clean all of the grit from the rocks, barrel, and lid (don't let any grit go down the drain). At this point in the tumbling process, a dry rock should have a smooth frosted surface. Inspect the rocks, looking for any that are cracked or broken. If found, they are discarded or saved for the next time we run Step 1.
Used grit and rock mud should never be washed down a drain. It can clog your plumbing system. We wash rocks in a plastic colander over a plastic bucket to keep the mud out of the drain.
STEP 3 - Fine Grind / Pre-polish
The third step of the four-step tumbling process is a week in a fine grit such as 600 grit or 500 grit silicon carbide. Begin with a barrel that is perfectly clean. Place your rough and any ceramics that are with them into the barrel, and add two level tablespoons of fine grit per pound of material. Then add water until it fills the barrel up to just below the top of the rocks. Run this for about seven days, and then do a thorough cleaning of the rocks, the barrel, and the lid.
Remove any rocks that have broken or show signs of fracturing. At this point in the process, the rocks should be extremely smooth, and some of them might display a slight luster.
Be very clean! Before you replace the lid on your barrel, be sure that both the lid and the rim are perfectly clean. This will allow the lid to fit tightly and prevent leaks.
STEP 4 - Polish
Now you are down to the final step - the one that puts a bright shine onto your tumbled stones. Be sure that the rocks and the equipment are perfectly clean. (Some people have an extra barrel that they use only for the polishing step.) A few specks of grit could ruin a great polish.
Place the rocks in the barrel and add two level tablespoons of rock polish (we use TXP aluminum oxide powder for almost all of our rotary tumbling) per pound of material in the barrel. Add water to just below the top of the rocks. Then, close the barrel and run for about seven days.
When you finish this step, your rocks should be bright and shiny. If they are, congratulations! Admire them for a while and share them with your friends.
If the stones have an extremely smooth surface but do not shine, they might need cleaned up using the burnishing step described below. If they have scratches on them, then you will need to go back to STEP 2 and repeat the medium grind, fine grind, and polishing steps.
For burnishing we grate up a bar of Ivory Soap with a vegetable grater. Then we add 1/2 tablespoon of grated soap for each pound of rock plus enough warm water to almost cover the rocks. See our video about burnishing polished stones.
Sometimes our stones are a little "hazy" when they come out of the polish, or small particles of polish are in micro-size crevices. We shine and clean them up by tumbling for an hour or so in soapy water. This is called "burnishing."
To burnish we place the stones in our polish barrel with the normal amount of water and then we add about 1/2 tablespoon of grated "Ivory" bar soap for each pound of rock (we use "ORIGINAL" Ivory soap - don't use a soap with aloe or abrasive or any other additive - honestly, just get a bar of Ivory soap). Burnishing usually makes the tumbled stones a little brighter, but sometimes it really kicks up the shine.
Print a copy of our free tumbling log and use it to keep your records.
Here are a few of our favorite tumbled stones!
It is easy to forget what day you started the tumbler or what type of grit was used - especially if you are running multiple tumblers. Keeping records will keep you on track and provide a history that will help you learn. We record material tumbled, start date, abrasive used, media used, finishing date and duration, along with any comments or observations about the results.
To help you with your record keeping, we have prepared a printable tumbling log.
We usually have multiple tumblers running here and we record every barrel of rock that we tumble on these logs. Even if your memory is better than ours, record-keeping is a good idea. When you learn something that works or something that doesn't, you will have it recorded. This information can help you repeat great results and avoid repeating bad ones. Also, we have trouble remembering which day a barrel of rocks was started. Using the log takes away the chance of forgetting.
|Hobart M. King has decades of rock tumbling experience and writes most of the articles on RockTumbler.com. He has a PhD in geology and is a GIA graduate gemologist. He also writes the articles about rocks, minerals and gems on Geology.com.|
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Technique for smoothing and polishing a rough surface on relatively small parts
Tumble finishing, also known as tumbling or rumbling, is a technique for smoothing and polishing a rough surface on relatively small parts. In the field of metalworking, a similar process called barreling, or barrel finishing, works upon the same principles.
Tumbled stones are made with rock tumblers in a process very similar to the natural processes that produce "sea glass" or "beach glass".
Tumbling of rocks as a lapidary technique for rock polishing usually requires a plastic or rubber-lined barrel loaded with a consignment of rocks, all of similar or the same hardness, some abrasivegrit, and a liquid lubricant. Silicon carbide grit is commonly used, and water is a universal lubricant. The barrel is then placed upon slowly rotating rails so that it rotates. The optimal speed of rotation depends on the size of the tumbler barrel and materials involved. Vibratory finishing process can be used instead.
A well-chosen speed for stone polishing causes the rocks within the barrel to slide past each other, with the abrasive grit between them. The result of this depends on the coarseness of the abrasive, and the duration of the tumble.
Typically, a full tumble polish from rough rock to polish takes 3–5 weeks, and is done in a minimum of 3 steps. Initially, the rocks are smoothed with a coarse grit (such as 60-90 mesh). The idea behind the first step is to take rough rock or stone and grind it (tumble it) down into a form which is indistinguishable (in shape) from the final product. This is followed by washing and then a stage of finer grits (120-220 then 400-600 mesh), before the (optional) use of a pre-polishing compound (1200 grit), a washing cycle with detergent to remove any grit on the stones. The final step is a polishing stage using powdered polish, (such as cerium oxide or tin oxide), water, and often small plastic pellets that are designed to cushion the stones as they tumble (so as not to cause chipping) and carry the polish evenly across the stones.
The precise tumbling duration is determined by many factors, including the hardness of the rock and the degree of smoothing desired in the coarser steps. Some people will tumble stones with rough grit for two, three or even four weeks to get their desired shapes out of the stones.
There are two main types of rock tumbling: barrel (rotary) tumbling, and vibratory tumbling. Rotary tumbling is more common, simpler, quieter and less expensive than vibratory tumblers. There are two differentiating factors, however, that may lead one to use a vibratory tumbler. First, vibratory tumblers retain the overall shape of the rough rock, whereas rotary tumblers tend to make rocks round. Thus, it is important to use vibratory tumblers to make faceted shapes and tear drop forms. Second, vibratory tumblers tend to work much faster than rotary tumblers, generally reducing the processing time to half.
In the polishing step, rock polish is added in place of grit as well as the plastic tumbling pellets. After further tumbling, the rocks should now have a shiny look when dry. If this is not the case and the rocks appear to have a film on them, a burnishing step may be necessary. In burnishing, the rocks are tumbled with only the plastic pellets and the addition of an oil-free non-abrasive soap.
Sometimes, stone "preforms" are used. These are shapes cut from the rough rock before tumbling. This gives more control over the final piece, so shapes such as a tear drop can be produced. The technique is still limited to rounded shapes. Preforms may use less time with the coarsest step, or skip it altogether.
During the 1970s, small rock tumblers were a common hobby item, and jewelry decorated with tumbled semi-precious stones was very much in fashion. Likewise, dishes and decorative glass jars filled with tumbled stones (often including common rocks not suitable even for costume jewelry) were frequently used as household ornaments.
See also: Mass finishing
Metal tumbling is used to burnish, deburr, clean, radius, de-flash, descale, remove rust, polish, brighten, surface harden, prepare parts for further finishing, and break off die cast runners. The process is fairly simple: a horizontal barrel is filled with the parts which is then rotated. Variations of this process usually include media, water, or other lubricants. As the barrel is rotated the material rises until gravity causes the uppermost layer to landslide down to the other side. The barrel may also have vanes, typically made of rubber, which run along the inside of the barrel. As the barrel turns the vanes catch and lift the parts, which eventually slide down or fall.
In a wet processes a compound, lubricant, or barreling soap is added to aid the finishing process, prevent rusting, and to clean parts. A wide variety of media is available to achieve the desired finished product. Common media materials include: sand, granite chips, slag, steel, ceramics, and synthetics. Moreover, these materials are available in a wide variety of shapes. Usually different shapes are used in the same load to reach into every geometry of the part.
Tumbling is an economical finishing process because large batches of parts can be run with little or no supervision by the operator. A full cycle can take anywhere from 6 to 24 hours with the barrel turning at 20 to 38 RPM. Tumbling is usually most efficient with the barrel half full. Some processes also use a filter system to allow parts or other materials in the cylinder to be separated.
The disadvantages of this process are that the abrasive action cannot be limited to only certain areas of the part, cycle times are long, and the process is noisy.
Barrel burnishing is a type of barreling where no cutting action is desired. The goal is to reduce minute irregularities and produce a clean, smooth surface. The parts are usually tumbled against themselves or with steel balls, shot, rounded-end pins, or ballcones to achieve this. It is also usually a wet process that uses water and a lubricant or cleaning agent, such as soap or cream of tartar. The barrel is not loaded more than half full and if media is used then a 2:1 ratio of media to parts is maintained to keep the parts from rubbing.
Centrifugal barrel tumbling uses a tumbling barrel at the end of a rotating arm to add centrifugal forces to the barreling process. This can accelerate the process 25 to 50 times.
Spindle finishing mounts the workpieces onto spindles that rotate the parts opposite that of the media flow. This prevents the parts from interacting with each other and accelerates the cycle time, but extra time and cost are required to fixture the workpieces.
Stained glass shards used for mosaic glass are also tumbled. No abrasive is used, to avoid clouding the glass; there is only water as a lubricant. The object of this tumbling is to remove the sharp edges from the glass, so that it may be handled safely. As little as 8 hours of tumbling may be sufficient for tumbled glass.
Tumbling is used to polish and smooth dice for recreational use, but it has the unfortunate effect of making their sides and faces somewhat uneven and thus making the dice less than fair.
Tumbling can be used in 3D printing to correct small artifacts on the printed objects, such as visible layers.
These techniques, although they take a long time, involve very little operator intervention and thus are very cheap. Small tumblers (one pound capacity) are available and inexpensive for home/hobbyist use. At the other end of the scale, professionals can use very large barrels to do a lot of work at once. The main disadvantage of tumbling is its limited scope - stones will be smooth and have semi-random shapes (like pebbles from the beach), and metals need to be relatively simple shapes, with no fine work.
- Ball mill, a process with some similarities to tumble polishing
- Degarmo, E. Paul; Black, J T.; Kohser, Ronald A. (2003), Materials and Processes in Manufacturing (9th ed.), Wiley, ISBN .
Rock tumbling is the hobby of collecting a wide range of rocks and turning them into beautiful gemstones you can use to make jewelry, crafts, decorations, or just to collect for fun.
It’s a pretty simple hobby that can be enjoyed at home by the entire family. All you need is a tumbler, some rocks, and a few other inexpensive materials.
Have you ever picked up a rock on the beach or a river bed that was perfectly rounded and smooth to the touch?
That’s a rock that has been ‘tumbled’ by mother nature (water and sand) over the course of hundreds and even thousands of years.
Rock tumbling as a hobby is the exact same process. The thousand years it would take nature to tumble a rock can easily be done at home in a matter of weeks.
Now that’s pretty neat!
In this guide:
What is a rock tumbler?
A rock tumbler is a very simple device.
It’s a small machine that turns a barrel round and round non-stop for weeks at a time.
Inside the barrel are your rocks, water, and grit. The grit is what makes your rocks smooth and acts as the sand that nature uses to smooth and polish your rocks.
Grit comes in several levels of coarseness. Think of it like sandpaper.
When you start your project, you’ll want to use a very coarse grit to knock down the sharp edges of your rocks.
Then every couple of weeks, you’ll move on to a slightly finer grit until you reach the final stage where the grit is almost like a fine powder.
Check out our in-depth article all about rock tumbler grit.
A brief history of rock tumblers
While nature has been tumbling rocks for millions of years, rock tumbling machines have only been around since the 1950s.
It was a way to take uncut rocks from nature, and turn them into gemstones that could be made into jewelry.
The process of rock tumbling gained popularity very quickly. By the 1960s, dozens of companies in the U.S had begun to manufacture tumblers.
Barrels of tumblers were first made out of paint cans and eventually evolved to use better materials like rubber and plastic.
While the industry started with dozens of manufacturers, only two were able to rise to the top and become the brands of choice: Lortone and Thumler’s.
Both of these brands still exist today and cater to both rockhound hobbyists and lapidary professionals.
In addition to the professional-grade tumblers, there are a few brands of ‘toy’ tumblers that are perfect for kids. The more well-known brands are National Geographic and Smithsonian.
What to do with tumbled rocks
You’ll find that people love rock tumbling for a number of reasons.
While many folks just love collecting a wide range of rocks to hold and display proudly, there are lots of other reasons why people get into rock tumbling.
Here are some of the more common uses for tumbled rocks:
- Jewelry making
- Various craft making
- Vase/planter filler
- Holiday decorations
Where to find rocks to tumble
Now that you know the basics of rock tumbling and what you can do with tumbled stones, let’s talk about how and where to find rocks.
What makes a rock good for tumbling?
It should be very hard, nonporous, and have a somewhat smooth surface (i.e., not gritty).
Some of the more popular types of rocks that fit these characteristics are agate and jasper – both common forms of quartz. See my guide to the best rocks to tumble.
While you can buy any of these rocks online or at your local rock shop, I personally find it way more exciting to find them in nature (although not always realistic). For me, the thrill of the hunt is a big part of rock tumbling.
Agate is probably the most popular rock to work with because it’s translucent and has so many unique patterns and designs. It’s a type of quartz and shines up to be real beauties.
In the United States, agate is typically found in Western states – particularly in Oregon, Arizona, Montana, Wyoming, South Dakota, and Michigan.
These rocks are typically found in coastal areas, lakes, and places with a past of volcanic activity.
It’s best to visit rocky beaches during low tide. Sometimes the agates will be laying right on top and other times they’ll be buried between other rocks. Either way, they’re pretty easy to spot.
I love this video of Tim Blair finding agates on some rocky Washington beaches.
Jasper is another form of quartz that’s quite popular and easy to find. In the United States, it’s also most commonly found in Western states like Oregon, Idaho, Washington, California, Arizona, and Utah. You can also find them in Texas and Arkansas.
As with any rock hunting, your best bet will be to pick up a guidebook for your area to see what’s abundant, and how best to find them.
Which rocks NOT to tumble
As I talked about above, you want to pick rocks based on their hardness according to the Mohs scale.
The Mohs scale was formed in 1812 by Friedrich Mohs (a German geologist).
In a nutshell, it’s a scale from 1-10 that measures a rock’s scratch resistance (or hardness).
The lower the number, the softer the rock. For tumbling, it’s best to stay in the seven range.
This is where quartz falls.
Here is a great visual from the National Park Service.
You can see that talc is so soft that it can be scratched with just a fingernail. Harder minerals require steel nails and masonry drill bits to leave a scratch.
Rocks that are too soft or too hard can be tough to polish and not recommended for a beginner.
Examples of rocks that are too soft would be soapstone and marble. Examples of rocks that would be considered too hard would be gem varieties of corundum like ruby and sapphire.
Diamonds would also be considered too hard.
Types of rock tumblers
There are two different types of rock tumblers – rotary and vibratory.
Rotary tumblers are much more common and best for beginners. When most people picture a rock tumbler, they’re thinking of a rotary.
This is the type of tumbler that will knock off the edges, shape, and smooth out rough rocks during the coarse grind stage.
Rocks tumbled in a rotary tumbler will change shape and become rounded.
Vibratory tumblers are less common with beginners and are typically used for fine polishing rocks you’ve already shaped. A vibratory tumbler will not shape your rocks like a rotary tumbler.
If you just want to polish your rocks and maintain the same shape and angles, then a vibratory tumbler may be for you.
The main advantage of a vibratory tumbler is that it dramatically speeds up the tumbling process for stages AFTER your rocks have been shaped (i.e., medium grind, fine grind, and polish).
So while each of the four stages in a rotary tumbler can take a week on average, stages 2-4 can all be done in only one week.
An ideal setup would be to buy both a rotary and vibratory tumbler.
This way you can do your coarse grind and shaping during the first week in your rotary, then switch over to your vibratory the next week to handle the other stages.
If you’re buying a rock tumbler for the first time, go with a rotary.
Best rotary tumblers
Rotary tumblers range in size and price depending on how many rocks you want to tumble at the same time.
Sizing is expressed in pounds. A three-pound tumbler will hold about two pounds of rock (and one pound of water and grit).
You can also get a double-barrel rotary tumbler.
These are great if you’re tumbling two different kinds of rocks at the same time especially if they’re a different hardness.
Remember, always tumble rocks together of similar hardness. This is especially true in the polish stages.
If you really wanted, you could tumble rocks together of different hardness in stages one and two. But be sure to separate them before stage three and four!
Another good reason to have a double barrel tumbler is if you have two batches of rocks in different stages.
So for example, if you start the coarse grind process on one batch, then a week later you want to start another batch. You can use one barrel for the new batch’s coarse grind, and use the second barrel for first batch’s medium grind.
It’s like having two tumblers for the price of one!
If you’re just looking to tumble a larger amount of rocks as one batch, don’t buy a double barrel. It’s much easier to manage a single barrel that’s double the size (only one barrel to clean and maintain).
The two brands you want to look for when buying a rotary rock tumbler are Lortone and Thumler’s.
The most popular Lortone tumbler for beginners is the 3A Single Barrel rotary.
See our complete guide on Lortone tumblers here.
The most popular beginner rotary tumbler from Thumler is the Model T 3lb single barrel.
Thumler’s also makes a very popular mid-sized tumbler called the Model B. You can read our review here.
Both of these tumblers have 3 lb barrels. You can’t go wrong with either.
Once you’ve picked out your tumbler, you’ll need a few more supplies such as:
When you’re first starting out, stick to the simple four-step process (coarse, medium/fine, pre-polish, and polish).
The four stages of grit you’ll want to use are:
- 60/90 silicon carbide for initial grinding and shaping of rocks.
- 120/220 silicon carbide for smoothing surface after initial shaping.
- Pre-polish aluminum oxide for preparing rocks for the final polish.
- Polish aluminum oxide for the final polish.
The exact type of grit may differ depending on which tumbler you’re using so always refer to the instruction manual that comes with your machine.
You can buy all four levels of grit as a kit from your local rock shop or on Amazon.
You’ll want to have these on hand for small tumble loads when you don’t have enough rocks to fill the entire barrel. These are great for taking up the empty space in the tumbler and help to deliver more of the polish to your rocks.
Pellets also help to ‘cushion’ the impact of rocks in your tumbler, and can even speed up the process since they encourage more tumbling and less sliding in the barrel.
One batch of these is all you need to last quite a while as they can be reused. Also, pellets should only be used in rotary tumblers – never in vibratory.
As an alternative to plastic pellets, some folks like to use other materials like corn or walnut shells.
If you end up becoming a serious rockhound, you may eventually look into things like slab saws, trim saws, arbors, and oscillating laps. But we’ll save those tools for another time since this guide is for the beginner!
Four stage tumbling process
Now that you have your tumbler and all the supplies you’ll need, let’s go into more detail about each of the four stages of rock tumbling.
Stage 1 – Shaping
As I’ve mentioned a few times already, the first step of the process is shaping with coarse grit. This will remove the rough edges from your rocks and give them a round shape.
To start, fill your barrel about half to two-thirds of the way full. For the best results, you should try to use various size rocks.
If you don’t have enough rocks to fill the barrel, be sure to add your plastic pellets after adding the rocks.
You should also add pellets at this stage if your rocks are fragile or have a flat shape.
The next step is to add your coarse grit (about two tbsp per pound of rock) followed by water to nearly the top edge of your rocks. Close the barrel firmly and clean up any water or debris.
Not everyone will do this next step, but I like to weigh my barrel before starting the machine. Every tumbler has a maximum weight. It’s important to stay under this weight, so you don’t wear out the motor.
Put the barrel on the tumbler, plug her in, and get going!
I should mention here that tumblers can be noisy so you should probably set up in either your garage or basement – or even a shed if it has electricity.
After a few days, you’ll want to check the progress to make sure the edges are being knocked down.
Then after your rocks have been tumbling for about a full week, and they are the shape you want them to be, remove your rocks from the barrel and rinse in a clean bucket of water.
Note that your time may vary depending on the type of rocks you’re tumbling. Harder rocks and rocks with strong angles will take longer to shape than softer, smoother rocks.
If your rocks aren’t the desired shape after the first week, just put them back in for as long as it takes. Just be sure to check on them every day or so.
At this stage, you’ll also want to clean out the barrel with soap and water as you prepare the rocks for stage two of the process. You’ll want to make sure all of the coarse grit is cleaned out of the barrel.
You want to be 100% sure all of the grit is out of the barrel, so you’re not mixing coarse grit with the fine. Some people will even go so far as to use separate sponges for each type of grit when cleaning their barrel.
At all stages of cleaning, don’t ever dump your waste products (slurry) down the drain – unless you happen to be a plumber and like repairing pipes 🙂
Once clean, it’s time to move onto the finer grit.
Stage 2 – Medium/fine grit
Follow the same process as before, again adding pellets if needed. Be sure to clean the pellets good because grit will stick to them. Sometimes it’s easier just to use a new batch of pellets.
Stage two (the finer grit) should take about the same amount of time as stage one.
What you’re looking for here is to remove any visible scratches/cracks/pits and to create a dull glow on the rocks when they’re dry.
Since time here will vary, you should check on your rocks every day or so to see how they’re progressing.
After another full cleaning, stage three is the pre-polish stage.
Stage 3 – Pre-polish
The purpose here is to make your rocks silky smooth and start to bring out a bit of luster.
This stage should also take about a week, but mileage may vary.
One last full cleaning and we’re onto the final stage – polish!
Stage 4 – Polish
This stage is going to use a grit that looks like a fine powder. After another week in this stage, your rocks should come out with a bright shine and look absolutely stunning.
During the polish stage, you should consider using some plastic pellets to protect your rocks from hitting each other.
There’s nothing worse than ruining a batch of rocks after a month of processing!
Finally, there’s a bonus stage that’s not necessary but can boost the brightness of your rocks – especially with agates and jaspers.
It’s called burnishing and is considered an additional stage of polish.
Burnishing is the fifth stage of tumbling, but instead of using grit, you’re using some form of soap or powdered laundry detergent.
This will put even more shine on your rocks, brighten them up, and remove any haze and residue from the slurry.
If you’re not sure whether the burnish stage will add more brightness to your rocks, a simple test can be done.
Take one of your rocks and buff one side with a very soft cloth for 10-20 seconds.
If the side you buffed is shinier than the other sides, it will benefit from a burnishing stage.
Most people will either use borax or shaved layers of ivory bar soap.
Whatever you use, make sure there are no additives in the soap that will harm your rocks. Also, be sure to add your plastic pellets for protection.
The ratios here are the same as in the grit stages. About two tbsp per pound of rock is recommended.
All you need is 24 hours in a rotary tumbling during this stage. But the longer, the better!
Tip: during both the polish and burnish stage, you may want to batch your rock types.
Since you’ll mostly be tumbling types of quartz as a beginner, group them all together for these last two stages. Remove all other families of rock.
So there you have it. The complete process for tumbling rocks in your rotary tumbler. Expect to wait 3-6 weeks on average to complete the entire process.
Remember, patience is a virtue!
In this section, I want to address some of the more common questions I see about rock tumbling.
While each of these questions likely deserves their own post, I’ll try to be as brief as possible with my answers.
Can my rock tumbler be used for other things like shells, glass, or coins?
Absolutely! Let’s talk briefly about each of these.
You can tumble seashells in a rock tumbler – as long as they’re not too thin.
But you’ll want to change up the process a bit. The same process used for hard rocks will not work for shells.
Shells are very soft and fragile, so you’ll want to skip the coarse grit stage, and give very little time to stage two – if any.
Because shells are so fragile, you’ll want to fill your barrel up as much as possible, using as much filler as you can.
Since tumbling shells is more about the polish stages, you may want to consider a vibratory tumbler instead of a rotary.
Don’t you love walking on the beach and finding a piece of naturally tumbled sea glass? Well you can actually make your own sea glass at home in your rock tumbler
As a rule, you don’t want to tumble anything less than ¼” thick as it will just fall apart in your tumbler.
Stick to a thick glass like the kind found in stained glass windows or even landscaping glass.
You can even use glass that you find on the beach that nature has already started to tumble.
Glass is considered slightly harder than seashells, but still not as hard as your average quartz.
So you’ll want to be delicate in your tumbling process, and cut down on the time in each stage – especially stage one and two!
Like shells, be sure to use plenty of filler to cushion the glass.
If you’re into metal detecting and tend to find a lot of stained and crusty coins, you may want to throw them in the tumbler for a nice, clean shine.
My disclaimer to this is to never clean any coin of value. The moment you clean a coin, it’s no longer worth anything.
A rock tumbler will completely destroy the collector value of your coins.
Typically the coins you’ll want to clean in a tumbler are modern coins that aren’t worth more than their face value or melt value.
For modern clad that you just want to take to the coin machine at the bank, you’ll want to do a quick cleaning or the machine may reject the coins.
Like rocks, you’ll want to tumble coins in groups. For clad, this applies mostly to copper and zinc metals.
Do not mix copper with zinc!
Lincoln pennies that are 1982 and older are copper so you’ll have to separate them from 1983+ zinc pennies, all nickels, dimes and quarters.
Also, any dimes and quarters pre 1965 are silver, so separate those as well.
Instead of grit, a lot of people like to use aquarium gravel and dish soap. Limit your tumbling to a few hours maximum. That’s all you need for some shiny coins!
What magazines and online forums do you recommend?
Interested in a magazine subscription for rock tumbling? Check out some of these:
Want to join a forum where you can connect with fellow rock tumblers? I highly recommend the Rock Tumbling Hobby Forum.
What are some good media (or grit) substitutes?
Depending on what you’re tumbling, there are a few media substitutes you can try including:
- Ceramic pellets
- Aquarium gravel
- Walnut shells
- Corn cob
- Stainless steel bb’s
- Tile spacers
- Crushed glass
Please note that for this beginner’s guide, I do not recommend any of the above. Stick to the standard levels of grit recommended by your tumbler’s manufacture.
Whatever medium or filler you decide to go with, be sure it’s right for what you’re tumbling.
There’s no quicker way to damage your rocks than by using the wrong medium.
Where to buy roughs?
If finding rocks in nature isn’t your thing, or you don’t live near a source of the rocks you want to polish, then buy yourself some roughs.
Your local hobby or rock shop will be the best place to buy these since you can also talk to the owner and get some invaluable advice.
But since not everyone lives near a rock shop, most times it makes more sense to buy your roughs online at places like amazon.com.
There are also more specialized sites out there like therockshed.com.
How to maintain tumbler?
Since tumblers will be running 24 hours per day for weeks at a time, it’s important to properly maintain your machine.
Always follow the instructions in the manual of your tumbler. Here are a few general rules to remember:
- Always keep the outside of your barrel clean.
- Apply a very small amount of lubricating oil to the bearings every 30 days of operation.
- Make sure the drive belt has the proper level of tension – not too tight but not too loose.
Like anything else, the more you take care of your rock tumbler, the longer it will last.
How much grit to use?
The amount of grit you use will depend on the type of tumbler, the brand, size, tumbling stage and type/size/shape/hardness of rocks.
To give you a rough idea of how much grit you’ll need so you know how much to buy, you’ll typically want between 2-4 tbsp of coarse and medium grit for your average 3lb rotary tumbler.
For polish stages, usually about 4-6 tbsp for your average 3lb rotary tumbler.
These estimates assume you’re doing a full load of rocks.
Coarse and medium grit usually sells in 16oz containers while polish grit comes in 8-12oz containers.
Your best bet will be to buy a basic four stage kit on Amazon.
Again, there are so many factors at play here. This is just to give you a general idea, so you know how much grit to buy when getting started.
How much rock to use?
How much rock to use in your barrel will depend on the size of the barrel. As a rule of thumb, use 2lbs of rock for a 3lb barrel. The rest of the weight is for grit, filler, and water.
How loud is a tumbler?
A rock tumbler can be quite loud – especially the more inexpensive models typically marketed as toys.
Larger barrel tumblers processing larger rocks will naturally be louder since the large rocks are clanging around, making more noise.
Even small 3lb tumblers can be somewhat loud, so I recommend keeping your tumbler in a separate room altogether – especially a basement or garage.
Where to buy rock tumbling supplies?
I like to buy my supplies from amazon.com. However, you can also get your supplies from sites like rocktumbler.com or therockshed.com.
What is rock tumbling grit made of?
Rock tumbler grit comes in many forms, but the most common are silicon carbide and aluminum oxide.
Silicon carbide will be your coarse and medium grit while aluminum oxide will be your pre-polish and polish grits.
Both of these chemical compounds occur naturally and have been used as abrasives for a very long time.
How to polish rocks by hand without a tumbler?
Rocks that are already shaped and somewhat smooth can be polished by hand if you don’t have a tumbler.
Typically you’ll only want to hand polish soft rocks, as hard rocks will be almost impossible to do by hand.
One quick way to determine this is a simple scratch test.
Scratch the rock with something hard and sharp like a steel file. If you’re able to leave a permanent scratch on the rock, you have a soft rock which will hand polish well.
If you cannot leave a scratch, the rock is probably too hard and is not worth polishing by hand. Your best bet will be to use a tumbler.
All you need to hand polish is different grit levels of wet/dry sandpaper (or emery cloth) and soft polishing cloth material like felt or leather.
The type of sandpaper you want is wet/dry and is the same stuff used on cars. So visit your local auto body paint supply shop if you can’t find this online.
Which rock tumbler is best?
The best rock tumbler will depend on several factors so I can’t make a blanket statement here. It all depends on what you’re tumbling, how much of it, and your level of experience.
I have a separate post on the best rock tumblers for different scenarios which you can find here.
Generally speaking, the two brands I favor are Lortone and Thumler’s. If you’re looking for the best tumbler for kids, then check out this post.
Rock tumbling is a very fun and rewarding hobby that people of all ages can enjoy.
Whether you’re making and selling jewelry with your rocks or just want to spend some quality time with your family, consider getting yourself a tumbler and try it out for yourself.
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