Rock Tumbling Guide

Rock Tumbling Beginner's Guide

By Rock and Tumble Company

Rotary Tumbler

Patience

What is Rock Tumbling?

Rock tumbling is the process of turning natural rock into beautiful, polished gemstones. If you've ever picked up a smooth rock from a beach or river, you've actually found a rock that has been "tumbled" by mother nature. So when we combine rock and grit media into a tumbling machine, we are replicating this same natural process at home, wearing down the rough exterior of the rock to reveal the beautiful details beneath the surface. And with the right tools, materials, and instructions, rock tumbling is not just a rewarding experience, but accessible to all ages! Let’s help you get started!

What You'll Need

Rotary Tumbling Machine "Rock Tumbler Buying Guide"
Rocks
Grit & Media
Burnish (Optional)

How to Choose Rocks for Tumbling

Picking the right rocks to tumble is half the battle. While you can tumble almost any rock that can fit in the barrel, a rock tumbler is not a miracle worker. The better the material you have going in, the better your polish will be coming out. Good in, good out! So let’s go ahead and go over some important factors to look for when choosing what to put in your barrel.

Hard Rocks Polish Well

Tumbling gradually wears down the outer surface of the rocks until they are smooth, sometimes glossy, with a richer color. However, when tumbling softer rocks, this process can be too harsh to be effective, leaving you with a dull finish or even a scratched or pitted surface. For this reason, we recommend that beginners start with a mix of jaspers or agates specifically sized for tumbling. These types of rocks are known to produce beautiful gemstones and are fairly forgiving as you gain experience with the tumbling process. And, if you are looking for rocks in the wild, be sure to bring a pocket knife with you. If you can scratch the rock with the knife and leave a mark, it is likely too soft to polish well. If you can identify the rocks you are tumbling, the Mohs Hardness Scale serves as a great reference. The sweet spot on this scale for hardness falls between 6 and 7, where most agates and jaspers can be found. For softer rocks it is definitely possible to work towards a polish with a rotary tumbler, but your success will likely require an experienced eye and polishing by hand.

Tumble Rocks of Similar Hardness Together

If you are tumbling a mix of different rock types, be sure they are all roughly the same hardness. If we reference the Mohs Hardness Scale again, we recommend that you do not tumble stones more than 1 degree of hardness from each other. If, for example, you were to tumble a mix of Moss Agate, which is roughly a 6.5/7 on the scale, and Fluorite, which sits at a 4, you would find your Fluorite becoming scratched and bruised by contact with the agate. And because of the difference in hardness, the softer rock will lose material much faster than the harder rock, making it impractical to move them through the different stages together.

Avoid Thin, Porous, or Fractured Rocks

Many rocks have unique features that, unfortunately, make them difficult to tumble. The tumbling process only works on the surface of your stones, so deep pores or fractures will not become magically smooth and thin or cracked pieces that may break will more than likely damage your batch at later stages. If you are careful about spotting these features early and removing the problems pieces, you’ll find much more success reaching that glossy finish.

Use the Right Size

Many rocks have unique features that, unfortunately, make them difficult to tumble. The tumbling process only works on the surface of your stones, so deep pores or fractures will not become magically smooth and thin or cracked pieces that may break will more than likely damage your batch at later stages. If you are careful about spotting these features early and removing the problems pieces, you’ll find much more success reaching that glossy finish.

Be Patient

Rock tumbling is not a quick process, and this is especially true for the harder rocks we are recommending. In particular, the course grind Stage 1 is a crucial step in shaping your rocks and the only stage that really removes any material. Unless you are happy with the shape, color, and texture of your rocks revealed at this stage it will be important to rinse and repeat until you see the proper results. This can sometimes take as much as a month or two for harder rocks. Of course you can cut this time short, but recognize that the stages that follow are only meant to buff out the surface you’ve achieved from the course grind stage. Trust us, be patient with your course grind Stage 1 and make sure your rock surfaces have been worn down enough to reveal the color and formations you are looking for underneath before moving on.

How to Choose Rocks for Tumbling

Picking the right rocks to tumble is half the battle. While you can tumble almost any rock that can fit in the barrel, a rock tumbler is not a miracle worker. The better the material you have going in, the better your polish will be coming out. Good in, good out! So let’s go ahead and go over some important factors to look for when choosing what to put in your barrel.

Media Filler: Ceramic or Plastic?

Rock tumbling is not a quick process, and this is especially true for the harder rocks we are recommending. In particular, the course grind Stage 1 is a crucial step in shaping your rocks and the only stage that really removes any material. Unless you are happy with the shape, color, and texture of your rocks revealed at this stage it will be important to rinse and repeat until you see the proper results. This can sometimes take as much as a month or two for harder rocks. Of course you can cut this time short, but recognize that the stages that follow are only meant to buff out the surface you’ve achieved from the course grind stage. Trust us, be patient with your course grind Stage 1 and make sure your rock surfaces have been worn down enough to reveal the color and formations you are looking for underneath before moving on.

The 4 Stages of Rock Tumbling

The process of rock tumbling consists of different stages of finer and finer abrasive grit that slowly erodes the exterior of your rocks until the imperfections have become smooth, even glossy with a mirror-like finish. There is also a final, optional stage called burnishing, which takes very little time and is highly recommended to impart that clean shine to the rocks. We’ve broken down these stages below, assuming you are using a rotary tumbler.

Stage 1: Course Grind

Duration: 1 - 4 weeks, often longer

Course Grit: 80 Grade, or 60/90 Grade Silicon Carbide

Add approximately 2 tbsp of coarse grit for every pound of rock you are tumbling. You can still have success with a little less grit, but there is no way to speed up your progress by using more grit. For a 3lb barrel, 4 tbsp is perfect.
Add water to the barrel until the waterline is just below the top of the rocks.
Seal the barrel, making sure the sides of the barrel lid are clean so that the barrel will seal. Place your barrel on the rotating shafts and begin tumbling.
After approximately 7 days, your coarse grit should have worn down substantially and is no longer significantly shaping the rocks. Open your barrel and feel the slurry with your fingers. You should not be able to feel any particles of grit remaining. This indicates that the coarse grit has broken down.
Dump out your rocks and media, rinse off the slurry and stuck grit, and inspect your rocks for progress. You are looking for rounded edges, which are often not quite there after just 7 days for harder rocks. If this is the case you will repeat Stage 1 until you are happy with the rounding on your rocks and the evenness of the surface. Only then should you move on to Stage 2. (*Only the course grit of Stage 1 is abrasive enough to shape harder rocks by removing material. So be sure you are happy with the shape of your rocks before moving on to Stage 2, as these next stages are more about preparing the surface of the rocks and not about removing material.)
Lastly, be sure when you inspect your rocks that you remove any potential problem pieces, such as ones that are likely to fracture or trap grit. It’s smart to remove these earlier rather than later in the process to avoid damaging your better pieces.

Stage 2: Medium Grind

Duration: 1 week

Medium Grit: 110/220 or 220 Grade Silicon Carbide

The steps for Stage 2 are similar to Stage 1. Double check that you are not carrying over contaminates from Stage 1.
Add approximately 2 tbsp of medium grit for every pound of rock you are tumbling. For a 3lb barrel, 4 tbsp is on the mark.
Keep in mind, material will have been removed from your rocks in Stage 1, and if enough was removed, you may need to add media to fill in the empty space of your barrel to reach 2/3rds full to prevent impact bruising.
Add water to the barrel until the waterline is just below the top of the rocks and seal the barrel to begin tumbling.
After another 7 days, it is time to check your barrel. You are looking for your rocks to be substantially smoother with a frosted look to them.

Stage 3: Pre-Polish

Duration: 1 week

Fine Grit: 500 or 600 Grade Silicon Carbide or Aluminum Oxide

As the grit becomes finer, it becomes harder to clean between stages. These contaminants will ruin your polish, so it is worth it to be extra careful not to bring courser grit into the next stage.
Add 3 tbsp of fine grit for every pound. For a 3lb barrel, this will be about 6 tbsp.
Make sure your barrel is at least 2/3rds full, adding media if necessary.
Add water to just below the rocks and begin tumbling.
After 7 days, check your barrel. You are looking for a slight luster on your rocks, even when dry, and for them to be smooth to the touch. Check for signs of contamination, like frosting or scratches, as you may need to repeat a stage to renew your progress.

Stage 4: Polish

Duration: 1 - 3 weeks, often longer

Polish: 1 - 3 Micron Micro Alumina Oxide (22,000 grit)

In this final stage, extra fine micro alumina oxide is used to polish the stones and bring out that mirror-finish.
Add roughly 1.5 tbsp of polish per pound. For a 3lb barrel, this comes out to 3 tbsp total.
Make sure your barrel is at least 2/3rds full, adding media if necessary.
Add water to just below the rocks and begin tumbling.
After 7 days, check your barrel. You are looking for a lustrous finish on your rocks, even when dry. If you find your rocks aren’t quite there, we’ve found that repeating this stage for another week or two can help get you the rest of the way there. However, doing so should be at your discretion, as by this stage additional runs may not have any noticeable improvements. Sometimes dullness may mean that more time was needed in earlier stages.

Optional Stage 5: Burnish

Duration: 7 hours

Cleaner: Borax or Ivory Soap

Burnishing can give an extra kick to your polish, and has the added benefit of cleaning out your rocks by removing the small particles of polish that get stuck in fractures and crevices.
For this process, simply clean out your barrel and add a bit of borax detergent or ivory soap. You don’t need a lot. 0.5 tbsp per pound will do, or roughly 1 tbsp for a 3lb barrel.
Burnishing is fairly effective over just a couple hours, but we recommend being patient and letting it run for a full 7 hours for those nooks and crannies.

How to Choose Rocks for Tumbling

For all your patience and persistence, you’ve taken a rough rock and turned it into a polished gemstone! Sometimes the tumbling process can feel like a science experiment, but do not fret. With each tumble you’ll gain experience through tips, tricks, and good ol’ fashioned trial and error. And as you grow in this hobby, we just know you’ll become a master in no time! Tumble on!

Don’t forget to check out our other guides for more helpful information, as well as our wide selection of hand-picked tumbling rough rock and grit & media available.