Guide to Rock Tumbling
ROCK TUMBLING BEGINNER'S GUIDE
Rock tumbling is the process of turning normal looking rough rock into beautiful polished gemstones. If you've ever picked up a rounded rock at a beach or river, you've found a rock "tumbled" by mother nature.
Rock tumbling with a machine is a similar process, and with the right tools, materials and instructions, rock tumbling is an easy and fun hobby that both kids and adults can enjoy!
Check out some of the rocks that we've tumbled below. These are all agates and jaspers from around the world with a beautiful array of natural colors and patterns!
What You Need To Get Started With Rock Tumbling
How To Choose Rocks For Tumbling
Picking the right rocks to tumble is half the battle. A rock tumbler cannot work miracles, and the better the material you use going in, the better looking the polished stones you will get. For this reason, for beginners we recommend purchasing a mix of jaspers and agates especially chosen for tumbling. These rocks will be easier to polish, and known to produce beautiful gemstones! Below we list some of the important factors for picking out the right rocks.
Harder Rocks Polish Well
Most of the rocks found lying around are too soft to take a good polish. An easy way to see if a rock will polish is to try to scratch it with a pocket knife. It if doesn't scratch the rock, then it's probably hard enough to polish! On the Mohs hardness scale, stones around a 7 tend to polish easily and polish well. Most agates and jaspers will fall into this category.
We would recommend a beginner stick to tumbling easier materials when starting out. The entire tumbling process could take several months, and with unknown rocks, you typically don't realize they won't polish until the very end of the process. Many beginners that are new to tumbling want to tumble the rocks they've found themselves, without being certain whether or not these rocks will successfully take a polish. Unfortunately, many of these people ultimately become discouraged after waiting months for the tumbling process to complete and finding out their rocks didn't end up getting polished.
Tumble Rocks of Similar Hardness Together
Rocks of varying hardness oftentimes do not tumble well together, because the harder stones will scratch the softer stones. This can cause the softer stones to have a bruised, or frosted look after the tumbling process. Soft stones will also wear down much more quickly than the rest of the rocks, and very soft stones can quickly disintegrate in the barrel.
Avoid Rocks with Deep Fractures
Many rocks have deep internal fractures. Unfortunately tumbling cannot remove these fractures that run through the depth of the stone. On the bright side, these rocks with fractures can will still take the same polish, so you can choose to live with these imperfections. If you are a perfectionist, you can break the rocks along the deepest fractures with a hammer and chisel.
Use a Mix of Sizes
A tumbler should be loaded up with a mix of stones of various sizes. A three pound capacity barrel should have rocks ranging from 1/4 an inch up to roughly 2 inches in diameter.
Small rocks, stones that are less than 1/2 of an inch in diameter, are important in the tumbling process for two key reasons. These small stones should make up roughly 15 to 20% of the total amount of rocks you are tumbling.
- Small stones create points of contact between your rocks when they're rolling around in the barrel. It is when the grit gets trapped between your rocks that the tumbling action occurs. The more points of contact between your rocks, the faster and more efficient the tumbling process.
- Small stones also serve as a cushioning force that smooths out the tumbling action. An overly rough tumbling action means that the rocks are smashing against each other with too much force, which can cause bruising and chipping. Softer rocks in particular, need a gentler tumbling action.
We understand many people don't have small rocks readily available to use, especially those that are new to the hobby. Fortunately, there are many sources of material that can be used instead:
- Small ceramic media.
- River gravel often represents an abundant source of free small rocks that can be used.
- Pea gravel commonly sold at home improvement stores is a cheap source of small sized stones.
If it comes down to it, one can always try tumbling without the ideal mix of sizes. Usually, if you are using the right equipment, grit, and rocks that are easy to polish such as agates and jaspers, you should be able to get a good polish on the rocks given enough patience, even though the tumbling process won't be as efficient or smooth.
The 4 Step Rock Tumbling Process
The process of rock tumbling consists of 4 stages of finer and finer abrasive grit that slowly erodes and smooths down ever finer imperfections in rocks, until the surface of these rocks are so smooth as they exhibit a mirror like polish.
The final stage is called burnishing, which is used to impart a special shine to the rocks.
These instructions assume you are using a rotary tumbler as opposed to a vibratory tumbler, which is not suitable for coarse grinding.
Step 1: Coarse Grind
Step 2: Medium Grind
Step 3: Pre-polish
Step 4: Polish
Step 1 : The Coarse Grind
Stage Duration: 1 week to 3 months (depending on how rounded you prefer your polished rocks)
Filling the Rock Tumbler Barrel
Fill the barrel to approximately two-thirds full of the rocks you wish to tumble.
Add approximately 1 tablespoon of coarse grit for every pound of rock you are tumbling (see table below).
We recommend using 80 grit or 60/90 grit silicon carbide for our coarse grind.
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 is clean so that the barrel will seal. Simply wetting the lid and wiping it off with a tissue should be sufficient, it is not necessarily for the lid to be completely clean. However, if small rock fragments are trapped between the sides of the lid and barrel, it is possible for the barrel seal to be imperfect, causing your tumbling solution to slowly leak out while you're away. We've had this happen before and trust me, tumbling slurry creates a mess you don't want to clean up!
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.
Rough Botswana Agates Prior to Stage 1
After 2 Weeks in Stage 1
Grit Usage Per Barrel
Common Tumblers
Grit Per Barrel (Tablespoons)
3 Pound Barrel
Thumler Model T, A-R1. Lortone 3A, 33B
3 TBSP
6 Pound Barrel
Thumler A-R6, Lortone QT6
6 TBSP
15 Pound Barrel
Thumler Model B, A-R12
15 TBSP
Spend Time To Shape Rocks In Stage 1
For those who are new to tumbling, this is a critical point in the process that will have a large impact on how your rocks turn out. It is important to remember that the stage 1 coarse grind is where all the rounding and shaping of the stone happens. Any subsequent steps only remove the scratches in stone and apply a polish to the surface. As a result, the shape of the stone after step 1 will remain constant from here on out. Therefore, it is important to only remove stones from stage one only when you are happy with the shape of the stone.
Most instruction manuals that come with tumblers recommend only 1 to 2 weeks in stage one. This is largely an over-simplification of the tumbling process. Spending 1 week in the coarse grind stage will only remove about 3% of the material from your rocks. If you want your rocks to end up with a very well rounded look, you will generally have to remove about 30 to 50% of the material from the stone.
However, we understand the vast majority of beginners don't have the patience to wait upwards of 4 months to see their first batch of polished stones. Therefore, it is normal to rush the tumbling process by spending only 1 to 2 weeks in the coarse grind, which will allow you to finish your first batch in about a month. If tumbled correctly, your stones will still take a polish in the end. However, most stones will not be well rounded, and it is more difficult to get a fine polish on stones that still have imperfections after the coarse grind.
That being said, if you want your polished rocks quick, clean your stones and the barrel with water and get ready to move on to the next stage. If you want your stones to be more rounded, repeat Stage 1 by adding more grit and letting them tumble for a week. Finish with the coarse grind only when you're happy with the shape of the stones.
After 4 Weeks in Stage 1
After 7 Weeks in Stage 1
Disposing of Rock Slurry
When you're ready to move on to the next stage, dispose of the old rock slurry, which is made up of water, rock particles, and remaining grit. Importantly, never pour your slurry down the drain, whether it be the sink or the toilet. The slurry will harden and become concrete like very quickly, and is guaranteed to clog your pipes in short order.
Be thorough in cleaning both rocks and the tumbling barrel used with water. This is important to avoid contamination, which happens if coarser grit particles from Stage 1 are carried into Stage 2. This will cause the larger particles to leave scratches on the surface of the stone, making it impossible or at least harder, to get to a final polish.
Stones that have deep pits and cracks are notorious for trapping grit and causing contamination. We recommend either throwing said stones out, tumbling these stones for a long period of time to remove all pits, or washing these stones individually with a tooth brush.
Rocks covered with "rock slurry" after the coarse grind
The lid of the barrel should be wiped off to prevent leaks
Step 2 : The Medium Grind
Stage Duration: 1 week
How Much Medium Grit To Use
The second stage is called the fine grind, or sometimes called the medium grind.
Here we use a medium grit, typically around a 110/220 silicon carbide or 150/220 silicon carbide, to remove the scratches from the coarse grind. Use about 1 tablespoon of medium grit for each pound of rock in the barrel. One tablespoon of grit is equivalent to one ounce. Before the rocks go into the Stage 2 process, don't forget both the stones and barrel should be clean from the prior stage. If specks of coarse grit make it into the second stage grind, it could contaminate the process by scratching the stones.
How To Fill Up The Barrel
Similar to the Stage 1 grind, it is recommended to fill up the barrel to around 2/3 full. Depending on how long your rocks have been tumbling in Stage 1, however, you may be left a lot less material and may not have enough to fill your barrel. If this is the case, you may consider filling up the rest of the space with ceramic media. It is not essential for the barrel to be exactly 2/3 full, but if you stray too far from this threshold, you may not be able to create an ideal tumbling action.
After a week, the fine grind has been completed, and you can open up the barrel. Once again, clean the slurry off the rocks and barrel, being careful to avoid contamination of the next stage. Never pour left over slurry down the drain.
At this point, your rocks should have be quite smooth and have a frosted look to them.
Optional Advanced Technique: Skipping the fine grind process by spending a little extra time in the coarse grind stage (Stage 1).
Step 3 : Pre-Polish
Stage Duration: 1 week with a rotary tumbler, 2 to 3 days with a vibratory tumbler
Be Careful To Avoid Contamination
The third stage, often called the pre-polish stage, utilizes even finer grit, typically, around 500 grit silicon carbide or 500 grit aluminum oxide to remove the small scratches created by the Stage 2 grind. Similar to the start of Stage 2, make sure your barrel is clean at the beginning to avoid cross contamination from the coarser grits. Many hobbyists, ourselves included, prefer to own separate barrels for each stage of the process to avoid having to clean the barrels after each stage. However, for those that are new to the hobby, this adds unnecessary expenses.
Add one tablespoon of pre-polish grit to your barrel for each pound of rock tumbled.
Tumble for one week, and then clean out your rocks and barrel.
Be careful to avoid contamination of grit into the next stage. After the pre-polish stage your rocks should have a slight luster even when dry. You're almost there!
Step 4 : Polish
Stage Duration: 1 to 3 weeks with a rotary tumbler, 3 to 4 days with a vibratory tumbler
The final stage utilizes extra fine micro aluminum oxide to polish your stones.
Add one tablespoon of the micro aluminum oxide for each pound of rock tumbled.
Most instruction manuals for tumblers recommend only one week in this polish stage. We have personally found that you can get maybe 75% of an ideal polish by tumbling for one week, but the polish improves slightly each week thereafter, maxing out around week three.
When your polish is done, clean out your barrel and rocks. After the polish stage, your rocks should have a lustrous finish, even when dry.
Optional Final Step : Burnish
Burnishing can give an extra kick to your polish, and has the added benefit of helping to clean out your rocks by removing the small particles of polish that get stuck between fractures and crevices.
For this process, simply clean out the polishing barrel and add a bit of Borax detergent or ivory soap. You don't need a lot, approximately one teaspoon of soap or detergent per pound of rock is enough. Burnishing for an hour or two is sufficient.
Congratulations on your beautiful tumbled rocks!
Congratulations for the patience and persistence it took to produce your polished gems!
Rock tumbling is often an exercise in patience: frequently the more time you spend on the tumbling process, particularly the first stage, the easier it is to get a good polish, and the better your final shine will be.
Don't forget to check out some more of our tumbling tips and articles for more information, as well as our gallery with our own tumbled rocks!
ROCK TUMBLING BEGINNER'S GUIDE
Rock tumbling is the process of turning normal looking rough rock into beautiful polished gemstones. If you've ever picked up a rounded rock at a beach or river, you've found a rock "tumbled" by mother nature.
Rock tumbling with a machine is a similar process, and with the right tools, materials and instructions, rock tumbling is an easy and fun hobby that both kids and adults can enjoy!
Check out some of the rocks that we've tumbled below. These are all agates and jaspers from around the world with a beautiful array of natural colors and patterns!
How To Choose Rocks For Tumbling
Picking the right rocks to tumble is half the battle. A rock tumbler cannot work miracles, and the better the material you use going in, the better looking the polished stones you will get. For this reason, for beginners we recommend purchasing a mix of jaspers and agates especially chosen for tumbling. These rocks will be easier to polish, and known to produce beautiful gemstones! Below we list some of the important factors for picking out the right rocks.
Harder Rocks Polish Well
Most of the rocks found lying around are too soft to take a good polish. An easy way to see if a rock will polish is to try to scratch it with a pocket knife. It if doesn't scratch the rock, then it's probably hard enough to polish! On the Mohs hardness scale, stones around a 7 tend to polish easily and polish well. Most agates and jaspers will fall into this category.
We would recommend a beginner stick to tumbling easier materials when starting out. The entire tumbling process could take several months, and with unknown rocks, you typically don't realize they won't polish until the very end of the process. Many beginners that are new to tumbling want to tumble the rocks they've found themselves, without being certain whether or not these rocks will successfully take a polish. Unfortunately, many of these people ultimately become discouraged after waiting months for the tumbling process to complete and finding out their rocks didn't end up getting polished.
Tumble Rocks of Similar Hardness Together
Rocks of varying hardness oftentimes do not tumble well together, because the harder stones will scratch the softer stones. This can cause the softer stones to have a bruised, or frosted look after the tumbling process. Soft stones will also wear down much more quickly than the rest of the rocks, and very soft stones can quickly disintegrate in the barrel.
Avoid Rocks with Deep Fractures
Many rocks have deep internal fractures. Unfortunately tumbling cannot remove these fractures that run through the depth of the stone. On the bright side, these rocks with fractures can will still take the same polish, so you can choose to live with these imperfections. If you are a perfectionist, you can break the rocks along the deepest fractures with a hammer and chisel.
Use a Mix of Sizes
A tumbler should be loaded up with a mix of stones of various sizes. A three pound capacity barrel should have rocks ranging from 1/4 an inch up to roughly 2 inches in diameter.
Small rocks, stones that are less than 1/2 of an inch in diameter, are important in the tumbling process for two key reasons. These small stones should make up roughly 15 to 20% of the total amount of rocks you are tumbling.
- Small stones create points of contact between your rocks when they're rolling around in the barrel. It is when the grit gets trapped between your rocks that the tumbling action occurs. The more points of contact between your rocks, the faster and more efficient the tumbling process.
- Small stones also serve as a cushioning force that smooths out the tumbling action. An overly rough tumbling action means that the rocks are smashing against each other with too much force, which can cause bruising and chipping. Softer rocks in particular, need a gentler tumbling action.
We understand many people don't have small rocks readily available to use, especially those that are new to the hobby. Fortunately, there are many sources of material that can be used instead:
- Small ceramic media.
- River gravel often represents an abundant source of free small rocks that can be used.
- Pea gravel commonly sold at home improvement stores is a cheap source of small sized stones.
If it comes down to it, one can always try tumbling without the ideal mix of sizes. Usually, if you are using the right equipment, grit, and rocks that are easy to polish such as agates and jaspers, you should be able to get a good polish on the rocks given enough patience, even though the tumbling process won't be as efficient or smooth.
The 4 Step Rock Tumbling Process
The process of rock tumbling consists of 4 stages of finer and finer abrasive grit that slowly erodes and smooths down ever finer imperfections in rocks, until the surface of these rocks are so smooth as they exhibit a mirror like polish.
The final stage is called burnishing, which is used to impart a special shine to the rocks.
These instructions assume you are using a rotary tumbler as opposed to a vibratory tumbler, which is not suitable for coarse grinding.
Step 1: Coarse Grind
Step 2: Medium Grind
Step 3: Pre-polish
Step 4: Polish
Step 1 : The Coarse Grind
Stage Duration: 1 week to 3 months (depending on how rounded you prefer your polished rocks)
Filling the Rock Tumbler Barrel
Fill the barrel to approximately two-thirds full of the rocks you wish to tumble.
Add approximately 1 tablespoon of coarse grit for every pound of rock you are tumbling (see table below).
We recommend using 80 grit or 60/90 grit silicon carbide for our coarse grind.
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 is clean so that the barrel will seal. Simply wetting the lid and wiping it off with a tissue should be sufficient, it is not necessarily for the lid to be completely clean. However, if small rock fragments are trapped between the sides of the lid and barrel, it is possible for the barrel seal to be imperfect, causing your tumbling solution to slowly leak out while you're away. We've had this happen before and trust me, tumbling slurry creates a mess you don't want to clean up!
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.
Rough Botswana Agates Prior to Stage 1
After 2 Weeks in Stage 1
Grit Usage Per Barrel
Common Tumblers
Grit Per Barrel
3 Pound
Barrel
Thumler Model T, A-R1
Lortone 3A, 33B
3 TBSP
6 Pound
Barrel
Thumler A-R6, Lortone QT6
6 TBSP
15 Pound
Barrel
Thumler Model B, A-R12
15 TBSP
Spend Time To Shape Rocks In Stage 1
For those who are new to tumbling, this is a critical point in the process that will have a large impact on how your rocks turn out. It is important to remember that the stage 1 coarse grind is where all the rounding and shaping of the stone happens. Any subsequent steps only remove the scratches in stone and apply a polish to the surface. As a result, the shape of the stone after step 1 will remain constant from here on out. Therefore, it is important to only remove stones from stage one only when you are happy with the shape of the stone.
Most instruction manuals that come with tumblers recommend only 1 to 2 weeks in stage one. This is largely an over-simplification of the tumbling process. Spending 1 week in the coarse grind stage will only remove about 3% of the material from your rocks. If you want your rocks to end up with a very well rounded look, you will generally have to remove about 30 to 50% of the material from the stone.
However, we understand the vast majority of beginners don't have the patience to wait upwards of 4 months to see their first batch of polished stones. Therefore, it is normal to rush the tumbling process by spending only 1 to 2 weeks in the coarse grind, which will allow you to finish your first batch in about a month. If tumbled correctly, your stones will still take a polish in the end. However, most stones will not be well rounded, and it is more difficult to get a fine polish on stones that still have imperfections after the coarse grind.
That being said, if you want your polished rocks quick, clean your stones and the barrel with water and get ready to move on to the next stage. If you want your stones to be more rounded, repeat Stage 1 by adding more grit and letting them tumble for a week. Finish with the coarse grind only when you're happy with the shape of the stones.
After 4 Weeks in Stage 1
After 7 Weeks in Stage 1
Disposing of Rock Slurry
When you're ready to move on to the next stage, dispose of the old rock slurry, which is made up of water, rock particles, and remaining grit. Importantly, never pour your slurry down the drain, whether it be the sink or the toilet. The slurry will harden and become concrete like very quickly, and is guaranteed to clog your pipes in short order.
Be thorough in cleaning both rocks and the tumbling barrel used with water. This is important to avoid contamination, which happens if coarser grit particles from Stage 1 are carried into Stage 2. This will cause the larger particles to leave scratches on the surface of the stone, making it impossible or at least harder, to get to a final polish.
Stones that have deep pits and cracks are notorious for trapping grit and causing contamination. We recommend either throwing said stones out, tumbling these stones for a long period of time to remove all pits, or washing these stones individually with a tooth brush.
Rocks covered with "rock slurry" after the coarse grind
The lid of the barrel should be wiped off to prevent leaks
Step 2 : The Medium Grind
Stage Duration: 1 week
How Much Medium Grit To Use
The second stage is called the fine grind, or sometimes called the medium grind.
Here we use a medium grit, typically around a 110/220 silicon carbide or 150/220 silicon carbide, to remove the scratches from the coarse grind. Use about 1 tablespoon of medium grit for each pound of rock in the barrel. One tablespoon of grit is equivalent to one ounce. Before the rocks go into the Stage 2 process, don't forget both the stones and barrel should be clean from the prior stage. If specks of coarse grit make it into the second stage grind, it could contaminate the process by scratching the stones.
How To Fill Up The Barrel
Similar to the Stage 1 grind, it is recommended to fill up the barrel to around 2/3 full. Depending on how long your rocks have been tumbling in Stage 1, however, you may be left a lot less material and may not have enough to fill your barrel. If this is the case, you may consider filling up the rest of the space with ceramic media. It is not essential for the barrel to be exactly 2/3 full, but if you stray too far from this threshold, you may not be able to create an ideal tumbling action.
After a week, the fine grind has been completed, and you can open up the barrel. Once again, clean the slurry off the rocks and barrel, being careful to avoid contamination of the next stage. Never pour left over slurry down the drain.
At this point, your rocks should have be quite smooth and have a frosted look to them.
Optional Advanced Technique: Skipping the fine grind process by spending a little extra time in the coarse grind stage (Stage 1).
Step 3 : Pre-Polish
Stage Duration: 1 week with a rotary tumbler, 2 to 3 days with a vibratory tumbler
Be Careful To Avoid Contamination
The third stage, often called the pre-polish stage, utilizes even finer grit, typically, around 500 grit silicon carbide or 500 grit aluminum oxide to remove the small scratches created by the Stage 2 grind. Similar to the start of Stage 2, make sure your barrel is clean at the beginning to avoid cross contamination from the coarser grits. Many hobbyists, ourselves included, prefer to own separate barrels for each stage of the process to avoid having to clean the barrels after each stage. However, for those that are new to the hobby, this adds unnecessary expenses.
Add one tablespoon of pre-polish grit to your barrel for each pound of rock tumbled.
Tumble for one week, and then clean out your rocks and barrel.
Be careful to avoid contamination of grit into the next stage. After the pre-polish stage your rocks should have a slight luster even when dry. You're almost there!
Step 4 : Polish
Stage Duration: 1 to 3 weeks with a rotary tumbler, 3 to 4 days with a vibratory tumbler
The final stage utilizes extra fine micro aluminum oxide to polish your stones.
Add one tablespoon of the micro aluminum oxide for each pound of rock tumbled.
Most instruction manuals for tumblers recommend only one week in this polish stage. We have personally found that you can get maybe 75% of an ideal polish by tumbling for one week, but the polish improves slightly each week thereafter, maxing out around week three.
When your polish is done, clean out your barrel and rocks. After the polish stage, your rocks should have a lustrous finish, even when dry.
Optional Final Step : Burnish
Burnishing can give an extra kick to your polish, and has the added benefit of helping to clean out your rocks by removing the small particles of polish that get stuck between fractures and crevices.
For this process, simply clean out the polishing barrel and add a bit of Borax detergent or ivory soap. You don't need a lot, approximately one teaspoon of soap or detergent per pound of rock is enough. Burnishing for an hour or two is sufficient.
Congratulations on your beautiful tumbled rocks!
Congratulations for the patience and persistence it took to produce your polished gems!
Rock tumbling is often an exercise in patience: frequently the more time you spend on the tumbling process, particularly the first stage, the easier it is to get a good polish, and the better your final shine will be.
Don't forget to check out some more of our tumbling tips and articles for more information, as well as our gallery with our own tumbled rocks!