Rock Tumbling Secrets
Want to get some more great info on tumbling rocks? Check out our kit, “How to Polish Your Own Stones.”
Watch a short video about rock tumbling!
Rock Tumbling Secrets
There is a beach out on Whidbey Island (that’s in Puget Sound here in Washington state) that we love to take groups to in order to find the best assortment of stones and rocks for their collections or to study. We can find agates, lavas, serpentinite, quartzite, jasper, and so many others. The ocean has tumbled the rocks on the island. These rocks are so shiny and smooth, at least, while they are still wet.
But as soon as they dry off, they are dull, not even beginning to exhibit the brilliance of when they were wet. This is so often a disappointment to the kids, as they pick their samples with such care as to color, shape or size. But especially color.
Here’s a quick solution! Give the rocks a good coat of shellac or polyurethane that makes them appear to be polished. But the more permanent solution is to tumble them yourself to get that glorious shine!
Rock tumbling can be a very fun hobby. In fact, many folks have tried it, and almost as many have quit. It takes time, and many kids don’t want to wait 5-8 weeks for results! And there are tricks to getting it right, and often the instructions that come with your tumbler aren’t very clear about that. So with that in mind, and if you are one of those that wants to tumble rocks, here are some pointers for you!
Get a good rock tumbler!
First, and most importantly, don’t spend your money on a tumbler from a craft store, or even one of those that you can find in a museum. These are noisy, and often made of very inferior material that breaks easily. They may be good for one or two batches of rock tumbling, and then you are out of luck. A rubber barrel would be something good to look for. The noise that is generated will be significantly less. And be sure to get a tumbler from a reputable maker. We suggest Lortone, among others.
Where to put the tumbler?
We would suggest that you put the tumbler somewhere that won’t drive you to distraction. If you followed our advice and got a tumbler with a rubber barrel, then it may actually produce a rather soothing white noise. But soothing or not, we keep ours in the garage. You should also consider if it is convenient for you to get to in order to tend to it. It should not be out of sight, out of mind. That could be a mini catastrophe waiting to happen!
How do I choose rocks to tumble?
You need to choose rocks that are the same hardness for each batch that you do. If you are not familiar with this idea, be sure to look up what is the relative hardness of the stones you are tumbling. And be aware that some stones, like obsidian, are just too soft to tumble. Because you will have nothing left if you tumble them.
Also, mix the different sizes of stone. Small, medium and large. And mix jagged with smooth. You want to fill your tumbler about ¾ full. When you finish the whole process, a good deal of the stones will have been ground away, leaving the barrel only about half full. This is normal.
Can you identify those rocks?
Some of the fun in tumbling stones involves knowing rock types. You can learn how to identify rocks with our Rock Identification Made Easy Kit!
The First Step in Rock Tumbling
After you have selected your stones to polish, put them in the barrel, and fill the barrel with water to the top of the stones, and add the grit. After putting the stones in the tumbler, along with the appropriate grit, then you wait. I would suggest 10 days for each stage. Then you will clean out the grit at the end of each stage, and then put in a smaller grit and repeat the process. You will do this several times before you get to the finished product. And always be sure to clean out the barrel and the stones completely after each stage. You will go through three stages of tumbling, with three different grits, before you get to the polish stage.
Cleaning the grit out after each step is important!
First, don’t run the grit down your sink. That could be a costly plumbing bill, as the grit could harden in your pipes. Find a good place outside to rinse the grit, using a garden hose. And be sure to be very thorough. Any leftover grit in your stones will etch them as they go through the next phase. Your barrel, as well as the stones, need to be completely free of any residual grit. Use something like Tide powdered detergent to clean the tumbler after each step. Do not use a liquid detergent! It may leave residue that will etch your stones.
The Pre-Polish Stage
Now, before proceeding onto the polish stage, examine the stones for the “smoothness” factor. If you are satisfied with the smoothness of the stones (they should feel satiny, but have a dull finish), then place the stones into the barrel and again fill with water to the bottom of the top layer of stones. If, however, you are not satisfied with the smoothness of the stones, replace the stones and repeat this most recent (pre-polish) stage. This stage is crucial, as it sets up the stones for an effective polish. Add the appropriate pre-polish grit and tumble again continuously for 10 DAYS. If you are satisfied, go on to the next step. Be sure to remove any broken stones. Carrying them forward will scratch the other stones. They can be tumbled again in the next batch of stones.
The Polish Stage
Now, here is what you have been waiting for, the stage when you put a shine on the stones. After cleaning the barrel and stones thoroughly, place the stones back into the barrel, fill with water to the bottom of the top layer of the stones and add the appropriate amount of polishing grit. At this stage, the barrel usually has a lot of room left in it. So what now? Use some kind of media like small wooden pellets or plastic beads to fill some of the space.
Just a reminder. Above all, do not use pellets that have been used in a stage where you were using grit. Only use new pellets or clean pellets. The media will help carry the polish and also assure that your stones will not be scratched or damaged during the polish stage. If you only use this media for the polish stage, there is no need to clean it between batches. If you need media for your previous stages, use new or different media.
Tumble the stones on the polish stage for 10 days. At the end of this stage, take out a few of the stones, rinse them and check the shine. If you are satisfied with the shine, then you are ready for the burnishing stage. If you are not satisfied with the shine or the stones are dull in appearance, you will have to go back to the pre-polishing stage and repeat that stage. More polish will not help! More time will not help! You must repeat the pre-polishing stage. Be sure to clean your barrel thoroughly using something like Tide powder, as a dirty barrel may have contributed to the problem.
The Burnishing Stage
When beginning this stage, it is not necessary to clean the barrel or stones. Simply dump as much of the polish liquid as possible (not down your sink!), and then add water up to the bottom of the top layer of stones. Next, clean the lid and seal of the barrel so that there will be no leakage, and dry thoroughly. Before replacing the lid, add one cup of plain Tide powder detergent. Do not use a liquid detergent, as this will ruin your polished stones. Liquid detergent will scratch the newly polished stones! Reseal the barrel and let tumble for a day or so. Burnishing helps clean the stones and puts that extra shine on them. Remove the stones and enjoy what you have waited so long to appreciate! Then do it again.
And now you have it! Rock tumbling made easy! If you have specific questions, don’t hesitate to contact us for some sage advice!
Watch a short video from Rockman Pat about rock tumbling.
Check out other articles on our blog!
We have other short videos on geology at our YouTube channel!