New to rock tumbling? Not even sure what rock tumbling is? Welcome, you are in the right place!
- What is rock tumbling?
- Why tumble rocks?
- What do you need to start?
- Basic Tumbling “Recipe”
- Tumbling Tips
What is Rock Tumbling?
Rock tumbling is the process of eroding a rough rock surface away until it is smooth and shiny using either a rotary or vibratory tumbler. Rotary tumblers are simple machines that use an electric-powered motor to slowly turn a barrel.
Inside the barrel are the rocks, grit, and tumbling media. Vibratory tumblers achieve a similar goal by using vibrations to cause the rocks to wobble around and bump into each other. The principle is exactly the same for both tumblers.
The erosion is caused by the rocks rubbing against each other inside the tumbler barrel, which is why the tumbler needs to facilitate movement in order to work.
Grit is an abrasive powder that accelerates the erosion and speeds up the overall process. Tumbling media is usually small pieces of plastic, tile, or even other rocks that help fill the empty spaces in the tumbler and help deliver grit to all of the rock surfaces. It prevents the rocks from moving around too much and damaging each other. Rock tumbling is typically done in four separate phases:
- Shape rocks and remove rough edges
- Smooth surface
- Pre-polish
- Polish
The phases need to be separate because they each require a different type of grit. Depending on what type of rocks you are tumbling, the stages run anywhere from 7-21 days.
You might be wondering why this process takes so long. Think about this: have you ever found a smooth stone at the beach? That stone is smooth because it has been eroding away by waves and sand for years and years.
Rock tumbling is just way to accelerate and enhance that natural process. So rock tumblers actually work pretty quickly on a geological scale.
Why Tumble Rocks?
There are many different ways to use and appreciate rocks. I find that tumbling enhances the natural beauty of rocks by allowing you to see details that might otherwise be hidden by the rough surface.
Do I tumble all rocks that I find? Definitely not. Crystals can be found with beautiful naturally-occurring formations, and should be kept as they are. The rocks I usually choose for tumbling are broken fragments or rough pieces. Many rocks look completely different after they are polished.
Polished crystals can be used for spiritual healing or unique decoration. I personally love the experience of transforming rough rocks into perfect and smooth shapes. Keep a polished crystal in your pocket for good luck, leave it on your desk to fidget with when you’re bored, or leave them by your bed to ward off nightmares.
This is also a great activity for kids because it is safe, fun (parent supervision required), and can be a great way to get them interested in natural sciences.
What You Need to Start
My recommendation for beginners is to start with the National Geographic hobby tumbler. This package comes with everything you need to get started, and it even includes some really cool rocks! The basic requirements for rock tumbling are:
- Tumbler machine
- Silicon Carbide Grit 60, 220, and 500
- Fine Aluminum Oxide Polish Powder 1000 or 1200
- Rocks for tumbling!
The National Geographic kit includes all of these things as well as very clear and detailed instructions. This tumbler was my first rock tumbler and it definitely sparked my love for rock tumbling. The kit only includes enough grit for one full tumble, so you will need to buy more grit to continue using the tumbler after your first batch.
Here is more info if you want to check out other rock tumblers. I use SAKORANGE grit from Amazon, or you can also get more grit from National Geographic. There are also a few non-necessary supplies I recommend:
- Ceramic or plastic tumbling media
- Borax or Ivory soap
- National Geographic Gem Foam
The tumbling media is a really important, and will really improve results. Both ceramic and plastic media accomplish the same goal: to fill the the empty space inside the tumbler and cushion the rocks. If there is too much empty space inside the tumbler, the rocks can crash into each other which can result in chipping or breaking. The media also increases the contact within the tumbler which moves grit efficiently around the tumbler and can accelerate the tumbling process.
I believe plastic media is the best choice for function, and I use Polly Plastics Filler Pellets. These are great to use as filler, especially if you are tumbling fragile rocks like fluorite or obsidian. These pieces can be reused almost indefinitely, but they are restricted to use with the same grit. The grit sticks to the pellets and you can never truly wash it off, so you need to keep separate packs of pellets for each grit stage.
This makes switching rocks from one stage to another a little bit more of a hassle, not to mention the pellets are pretty small so spilling them is usually catastrophic. However, I am a perfectionist and I believe they do improve my results so I use them anyway.
Another option is ceramic media, which I also use frequently. These are small, cylindrical pieces of ceramic that provide the same function. They are more commonly used in vibrational tumbles because they help facilitate movement. National Geographic and Polly Plastics both sell ceramic media on Amazon.
Ivory soap and Borax are simple and cheap products to help improve tumbling results. I use them both to do a cleaning cycle between stages 2, 3, and 4. This helps prevent grit from sticking around with the rocks between stages. If course grit from stage 2 stays in the barrel during the fine polish stage 4, that grit could end up scratching up the rock surface and ruining the polish.
The National Geographic Gem Foam is also a good way to improve the shine of the polished rocks. This is an optional additional step that can be done at the end of the tumble. The gem foam definitely made my rocks more shiny, but I think that using Borax and soap achieves a similar goal. The Gem Foam is reusable for up to 10 tumbles.
Basic Tumbling “Recipe”
Now you have all the gear you need to start, so let’s begin! Please read all of the instructions that came with your tumbler before you begin. Find a nice place in your house, garage, or shed to keep the rock tumbler.
The tumbler needs to be plugged in at all times to run, and should run 24/7 if possible. Tumblers can be noisy, so choose a place far from your bedroom where it won’t be distracting. If you live in a small apartment, try sound-proofing a closet or cupboard with foam or blankets.
Place the tumbler on a smooth and flat surface, not carpet. Do not keep the tumbler outside. Most tumblers have electric motors and should not placed anywhere where they could get wet. If you keep the tumbler in a shed or garage, be mindful of the temperature. Check the manufacturer warnings about extreme heat, and remember that the water inside the barrel could freeze in extreme cold.
Now that your tumbler is ready to go, fill your tumbler barrel up 2/3 of the way full of rocks and add water until the rocks are just barely covered. Do not overload the weight limit specified for your tumbler, and remember that the weight capacity usually includes rocks, water, and grit.
Now add 2 tablespoons of grit per pound of rocks that you are tumbling. This weight does not include the water, so for a 3lb capacity barrel you usually have 2-2.5lbs of rocks. Seal your barrel tightly, give it a good shake, and let the tumbler get to work! The chart below outlines general tumbling timelines, but every batch will be different.
| Stage | Tumbling Time | Done When: |
| Silicon Carbide 60 or 90 grit | 7-14 days | Edges are rounded |
| Silicon Carbide 220 grit | 10-16 days | Surface is even |
| Silicon Carbide 500 grit | 7-14 days | Soft and smooth surface |
| Aluminum Oxide Polish 1000 or 1200 | 10-18 days | Surface is glossy |
When you are satisfied with your stones and ready to move on to the next phase, dump your barrel into a strainer. Important: do not dump the tumbler liquid or “sludge” down any household drain! The sludge will solidify and can cause major damage. You can safely dispose of the sludge by dumping it into a milk carton, letting it dry, and then throwing it in the garbage. You can also dump the liquid outside in a yard or driveway, just be sure not to lose any media pieces!
Next, rinse the stones, media and tumbler barrel well. Add the stones and media back to the barrel along with 2 tablespoons of grit for the next phase. Note that the stones will shrink during this process, especially during stage 1. You may need to add more tumbling media in the subsequent stages to keep the tumbler volume about 2/3 full.
Tumbling Tips
Rock tumbling is definitely a learn-as-you-go type of hobby, however, the following tips and tricks should help your first batch come out smooth and shiny!
1: Don’t overload the rock tumbler. The machines are designed to tumble a certain weight. Read and follow the instructions on the tumbler carefully. Ideally the tumbler barrel will be 2/3 full by volume, but different sizes or types of rocks will cause the overall weight to vary. The allowed weight on the rock tumbler usually includes grit and water, so don’t add 3lbs of rocks to a barrel with a 3lb weight limit. If you are overweight but unable to get the tumbler 2/3 full by volume, I suggest using a lightweight tumbling media like plastic pellets.
2: Don’t underload the rock tumbler. Yes this is sort-of a Goldilocks situation, and you want the barrel to be just right. If the barrel is below 1/2 full by volume then the rocks won’t have enough contact erosion, and they are more likely to crash into each other and break. It is OK if the barrel is lighter than the weight capacity, but try to ensure the proper volume is filled. The solution for this is also to add tumbling media of any kind or even more rocks!
3: Choose your rocks carefully. Yes, you definitely can walk into your driveway, grab a random handful of rocks, toss them in the tumbler, and hope for the best. There is nothing wrong with this, and I think it is fun to experiment and see what works and what doesn’t.
However, if you are looking to ensure that your rocks come out perfectly shiny and smooth, I don’t recommend this strategy. Hardness is an important geological concept that applies to rock tumbling. Not all rocks have the same hardness, and some rocks are actually so soft that you shouldn’t tumble them at all.
An easy rule-of-thumb is: if you can scratch the rock with your fingernail and leave a mark, then do not tumble it. This indicates the rock is way too soft to tumble. I usually sort my rocks using a piece of glass; a beer bottle or jar works perfectly fine.
I take my pile of rocks-in-question and try scratching the glass with the rock. If it leaves a mark then great! Put that rock in one pile. If it doesn’t scratch the glass then great! Put that rock in a different pile. You can tumble these two piles separately. Be wary of minerals that end in “ite” like fluorite or selenite. These stones actually dissolve in water and need special care when polishing or tumbling.
4. Size Matters. Contrary to what you might be thinking, bigger is not better in this case. Variability is actually the most important thing to consider when it comes to rock size. It is important to include different sizes of rocks in each batch, and no single rock should be larger than half the diameter of the tumbler barrel. Placing one large rock in your barrel will not work. Tumbling only 3 medium-sized rocks will not work very well. Tumbling a broad range of sizes will be the best to help the rocks move around inside the tumbler. If you don’t have any small rocks, ceramic or plastic tumbling media can act as substitute here.
5. Do a wash cycle between each grit stage. Rock tumbling is done in 4 or more separate stages for a reason. Each step is crucial and performs a different job. For that reason, you do not want any of the grit from one stage to be present in the next stage. The grit is very fine and can stick to plastic pellets, rocks, and the barrel. I recommend doing a wash cycle at least between stages 2, 3, and 4. I simply add Borax or Ivory soap (or both) and water to the rocks and media and tumble for 24 hours. If you are using plastic pieces, swap the pellets before the wash cycle.
6. Check one rock before you dump. Different types of rocks will need to tumble for different amounts of time. Many other factors such as grit quality or media can affect the time needed in each stage. I recommend that you always pull one rock out of the barrel, wash it off, and let it dry between each stage. By letting it dry you can see what state the rock is truly in. This will allow you to see if your rocks are ready to move on to the next step. If you dump the whole barrel and then notice that the rocks aren’t ready to move on, you will need to reload the barrel and add more grit, which is not the end of the world but I like to avoid it when possible.
7. Add more grit each week. The grit breaks during the tumble, which is the reason that the sludge that comes out of the tumbler cannot be reused as grit. If you have some decently hard stones like quartz or chalcedony, you may be tumbling for a few weeks per stage. I recommend adding an additional tablespoon or half tablespoon of grit (for a 3lb tumbler) every week that you tumble, or around halfway through your tumble if it is somewhere between 2 and 3 weeks long. This step will improve the tumbling results for that cycle.
8. Burnish the rocks at the end. No, this does not involve fire. Burnishing is a step done after the final polish stage to clean off the rocks and reveal that smooth, lustrous surface. This can be done a few different ways. You can add National Geographic Gem Foam to the barrel for 3 days at the end, which I found works very well. You can also just add Borax or soap, water and tumble overnight (yes, this is exactly the same as a wash cycle). Lastly, you can individually run each stone vigorously on a piece of rough fabric like denim.