Rock Tumbling – The top 5 mistakes to avoid

Sometime back I had made a small chain intended as a bracelet. The main reason was actually to practice my soldering given a chain has a stack of links all needing to be soldered together without getting soldered to the neighboring link. Great little exercise! The soldering went as well as could be expected but I ended up with a chain that needed some polishing on the inside of the links to look halfway decent.

So what to do? Well Google is your friend! I spent a couple of hours searching through all the different ideas from cotton on toothpicks, cotton string, specialty “hard to reach” polishing gismos until I found someone suggesting the use of a rock tumbler full of steel shots.

I did a bit more research and quickly realized that not only was a rock tumbler a pretty cool machine to have in the collection it would actually be quite useful for a bunch of different tasks like rock tumbling for one..!! but also to make “sea” glass i.e. the matted rounded pieces of glass you find on a beach and of cause jewelry polishing. Actually it’s burnishing but lets not get hung up on the semantics.

So I went on a hunt to find a good machine and after a further couple of hours I had been convinced that the 3A from Lortone was the right size and quality for what I needed. Actually check out the “Tumbling Rock & Jewelry” post to get an insight into what you need to consider when buying a tumbler.

Lortone A3 Rock Tumbler

So I found a place called Aussie Saphire Lapidary Warehouse (LINK: that were selling the Lortone machines here in Australia. Being a gadget that requires power I figured it would make sense to get it locally despite the added cost. We use 230V as opposed to 110V here in Australia. Although I have a 110V transformer (see Workshop Power Page) the cost of the machine in the US including shipping was not that much different from the local cost. So for this one I went local.

If you are in the US or some other country that Amazon is actually servicing Amazon is the way to go. They have the best prices by far.

The thing was that for me the most cost effective way to get the machine was buying a “Starter Pack”

This included all I needed for rock tumbling so I just added a bag of steel shots to the order and I was all set.

The machine turned up some days later and I was obviously keen to give rock tumbling a go. Although I primarily wanted to do tumble polishing of Jewelry I thought starting with rocks was a better way to get to know the machine initially.

So off I went with absolutely zero experience in the art of rock tumbling. Below are the first valuable lessons I learnt as part of this exercise.

Getting wrong size tumbler

Well I didn’t actually make this mistake per se but I can easily see how it would be tempting to get the biggest most powerful machine that you could lay your eyes on. But before pressing that “Purchases Now” button have a think through exactly how much material you will be tumbling at any one time.

The 3A has a capacity of 3 pounds (~1.3kg) for Jewlry making that is a STACK of rocks in one go. Even with the relatively heavy steel shots the smallest Lortone has ample capacity for the average Jewelry maker.

The thing is the larger the machine obviously the more room it takes up bit it would generally also use more power to drive a larger motor. Although not much you still have to take into account that these beasts runs constantly for weeks to achieve smooth rocks so it can add up.

So assess you actual needs and get the machine that best fits what you will be using it for.

Using the wrong rocks

The Starter pack I bought came with a tub of “gem rocks” to get started on. Not being crash hot on the geology side of things I obviously had no idea what the different rocks were. Well and I guess I really didn’t care as I was just going to run a test run anyway. But the lesson is that you want to carefully select the rocks you wish to tumble if you want to do it “for real” so here are some things you need to remember:

Choose rocks of approximately the same hardness otherwise you will see the soft rocks in a bundle be totally tumbled away before the harder rocks are even half smooth

Choose really hard dense rocks if you wish go the a high shine polish. The more porous rocks really don’t tumble all that well they will be rounded and nicely shaped but you will never achieve anything that looks like shine if the rock is soft or porous.

Choose rocks without cracks and strange shapes, Cracks in rocks will most of the time mean that the rock breaks up in the tumbling process or as soon as you start working with the finished rock. Either way it’s generally a waste of time. The odd shaped rocks will just take a lot longer to polish and in most cases result in the other rocks in the batch being over polished.

You can almost guess that I broke all the rules.. Well I actually didn’t know this before I just popped the entire batch of sample stones into the barrel and got started.

Using the wrong polishing compound

Rock Tumbling 17The polishing compound is also a rather important part of the process. As with sandpaper used for wood you go from a coarse grit to a really fine all the way to a polishing like compound to achieve the results you want.

There is a bewildering array of different types of grits and materials available for all types of applications. The main thing to pay attention to is really that you use the right grit and the right amount of polishing compound. I was lucky enough that the starter kit came with a booklet that outlined how much of each type of powder I needed to use. So I basically just blindly followed those instructions.

But if you want to experiment there are quite a few sites out there specializing in rock tumbling so they will be able to give you some ideas if you feel adventures. Check out the links in the Resources section

Not cleaning up probably

Rock Tumbling 14So I got the machine filled up and started. After the first 7 days worth of tumbling.. Yes you read that right 7 days and that was just the first of 3 or more equally long run times. So a thing I quickly learnt was that rock tumbling and my lack of patience was totally incompatible mind you as you will see below I may actually in this case have been a little to patient!

So after each block of tumbling you need to clean the rocks thoroughly to make sure none of the grit powder and polishing slurry (i.e. the thick grey soup the rocks are floating in) is carried across to the next run.

The thing you have to remember is that the grey soup is basically like a mud and if you wash off the rocks in your sink you WILL have to call the plumber to unclog your drains. So what I did was I cut a small piece of metal fly screen mesh and used that as my sift (obviously if you can nick a sift in the kitchen that will work even better) took the garden hose and washed the rocks outside in the garden.

Being too patient

Rock Tumbling 02When doing rock tumbling you have to be patient. As mentioned each tumble circle is on average 7-10 days and you have a minimum of 3-4 of these circles. So that is good month from start to finish. My advise is to find a place where the tumbler can be located without annoying anyone for this time. Although the machine is very quiet the rotation of the rocks will obviously create some noise.

On the patience side what I mean there is it will take time but don’t do like I did and let the rocks run for too long. I ended up with the polished rocks being at least 40-50% the size of the original rocks, which basically meant that some of the smaller more porous rocks had totally disappeared.

So there you go my first experience was not a total disaster but I wouldn’t class it as a success either I can see there is a lot more to it than just dumping some rocks in a container and letting the machine do its thing.

So if you have some tips or tricks you want to share drop a line in the comments below. I would like to hear your experiences with rock tumbling. Especially if anyone has a “recipe” for how to make sea glass as that will be my next project.