You be might think of a portal to the Nether, or Dragon Glass to combat White Walkers. Whichever it is, obsidian is mysterious, beautiful, and difficult to tumble.
Obsidian is an igneous stone formed from from rapidly cooled felsic (rich in feldspar and quartz) lava. It looks similar black or dark green glass, and has been used for centuries to make knife points arrowheads because it has no crystal structure, and can be easily chipped and shaped without cracking.
There are several types of this stone, including snowflake and rainbow obsidian. The rainbow variety has a mysterious iridescence caused by the presence of microscopic rods of hedenbergite crystal. I purchased these pieces from Rough Stone Rocks online specifically for the purpose of tumbling.
Let’s Get Ready To Tumble
This unique stone is relatively difficult to tumble, because like glass, it is fragile. These rocks are prone to chipping and breaking in a rock tumbler, so it is important to use tumbling media to cushion the rocks.
Obsidian is a relatively soft rock compared to minerals like quartz, meaning that it is best not to tumble obsidian with other types of rocks in the same barrel. It also means that these stones don’t need as much time to tumble.
I was very eager to tumble these stones because I wanted to see if they really had a rainbow shine. I hastily started the rocks in stage 1 without doing much prior research, but after about day 3 I started to wonder if I had made a mistake.
I read past experiences from other folks who tumbled obsidian and many accounts included just skipping stage 1 altogether and jumping right to stage 2.
I began to panic and pulled my rocks out at the end of day 3, which was several days earlier than I had intended. I figured that since most people skip stage 1, I should just skip now to stage 3 to avoid over-tumbling these fragile stones.
I decided run the stage 3 cycle for a longer time since I had completely skipped stage 2. I was also out of town during the stage 3 tumble, and my trip got extended several days resulting in an extra long tumble.
Something about this seemed familiar… (see My First Tumble). I moved the stones into the final polish stage even though something in the back of my mind was saying that this is not right.
I realized at the end that I made a big mistake by skipping stage 2. I have never found success by skipping stages, but to be fair I also have never tumbled anything as soft as obsidian before. Either way, my stones were dull; even after a burnish cycle.
To make things even worse, the stones tumbled for plenty of total time, but not enough time in the proper stages. This meant that the rocks were subjected to a lot of contact, which created nicks and cracks on the surfaces.
I immediately knew that I would have to start over with these. The best thing I could do was to start over at stage 2 and try again, and wonder if I even learned anything from my first tumble.
Before I got my first tumbler, I just had rocks… a lot of rocks. My wonderful friend noticed how I was bringing rocks home from every hike I went on, and gave me a National Geographic Hobby tumbler for Christmas. The hobby tumbler included enough grit for one full tumble and even came with a barrel full of rocks. I had been gathering rocks for so long that I immediately discarded the rocks that were included with the tumbler in favor of my collection of beautiful smooth stones from the beach. I was so eager to have polished stones, that I purposefully chose the smoothest stones to tumble first because they would take the least amount of time. And since the rocks were already very smooth, I decided it would be efficient to go ahead and skip grit stages one and two, and jump right ahead to the fine grit stages (which I would later regret).
I dutifully followed the instruction packet (except for the part where they recommend NOT skipping any stages) and started my rocks on an 8-day tumble. After (barely) waiting those 8 days I eagerly dumped my rocks to find that they were no closer to the smooth, glossy perfection I was hoping to achieve. Eager as I was, I did end up seriously questioning my decision to skip the first two grit stages. I did some research online and found that most experienced tumblers did not recommend completely skipping the course grit stages as I did. These stages are critical for shaping the rock surface and removing the tiny imperfections that inhibit a lustrous shine.
In my research, I found that I might have made more than one mistake. I decided to cut my losses and start the same rocks over again at stage 2. I was slightly disheartened to have wasted over a week, but at the same time I was glad to be learning this new trade. I continued my research and discovered the promised wonders of ceramic tumbling media. I bought one pound of the National Geographic brand and decided to give it a try. I let this batch of random sea rocks tumble for just under 6 weeks total, now allowing each stage to tumble for just over a week, and the polish cycle for two weeks. Of course, I had already used up all my stage 3 grit, so I had to buy more tumbling grit. I played it safe and purchased the National Geographic brand grit for consistency.
I was so excited for that final reveal after the polish stage. I had seen so many proud rock tumblers confidently dump the contents of their barrels into a strainer and spray to reveal beautiful, glossy stones. The day finally came, and I emptied my rocks into my metal strainer and washed them thoroughly with the hose. The hodgepodge of various beach rocks shone beautifully while wet, but I was terribly disappointed when I laid the stones out to dry. I noticed that the rocks adopted a matte finish and were scored with small white scratches. It took me longer than I would like to admit to realize that the metal strainer was the culprit. I immediately cursed my foolishness and made a mental note to buy a plastic strainer as soon as possible. In the meantime I used plastic wrap in the bottom of the metal strainer to protect the stones from any further damage. Even though that resolved the issue of the scratches, the dullness of the stones was a slightly more complicated issue to work out.
I took to the computer again to try and make sense of my apparent failure. I had followed all of the instructions this time around and even went beyond recommended tumbling times. I wouldn’t realize until much later on that the burnishing step after stage 4 is absolutely critical. After a full month of sulking over my matte rocks, I performed the 24-hour burnish cycle on my next batch of rocks and found that they came out absolutely perfect. I threw my original dull rocks back into the tumbler to see if burnishing was really the magic solution. The stones came out beautiful and shiny, just as I had hoped from the beginning. Even though the trial and error factor of this hobby can sometimes be frustrating, I always appreciate the experience of learning and improving. Watching each batch of rocks turn out better than the last is almost better than having every single batch turn out perfect…. almost.
Tumbling Recipe
I should have just followed the instructions that came with the National Geographic tumbler, but here is what I did instead:
Grit
Time
#3. Silicon Carbide 500 1 tbs
8 days
#2. Silicon Carbide 220 1tbs
8 days
#3. Silicon Carbide 500 1tbs
10 days
#4. Aluminum Oxide 1200 Polish 1tbs
14 days
National Geographic Gem Foam
3 days
Tumbling recipe
You might notice that I used grit 3 twice. I mistakenly thought it was OK to skip stages because my rocks were pretty smooth to begin with, but I was wrong. So I went back to stage 2 and followed the instructions from there on out. I didn’t do any wash cycles for this tumble, but I did scrub the rocks with a toothbrush before starting them on the final polish. I now know that doing a wash cycle is much easier and more effective. The National Geographic Gem Foam really improved my results, and before that step my rocks were dull. I was so disappointed at the end of the final polish, and I thought I had messed up the rocks completely. Luckily, rock tumbling is a relatively forgiving hobby, and it is actually really difficult to completely ruin the rocks. You can keep trying to make your rocks shiny after that final cycle is finished, even if it means completely starting over.
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.
https://www.instagram.com/p/CODjVcGB1J6/
Polished stones
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.
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.
https://www.instagram.com/p/CPapXoHBnuw/
Tumbled red poppy jasper
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.
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
General recommended tumbling times
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.
