Rock Tumblers Redux: Looking at the Stages of Tumbling

Several weeks ago, I posted an entry to the blog about how to work with your new rock tumbler (this of course assuming that you had received one at some point). Six weeks into my own experimenting with rock tumbler, I'm back with a few lessons and things that I've gleaned from my own experience, which I hope will be helpful to you.

Tumbling is typically a multi-week process, depending on the materials that you choose and the kind of polish that you are hoping to achieve. The choice of materials is important, as tumbling something rather hard with things that are soft will tend to result in the soft things being smashed down into tiny bits. To be certain of the hardness of the materials with which you are working, it's essential to have either a good rock & mineral field guide (I've got about a half dozen), all of which will give you the hardness of most anything you are likely to be tumbling, as presented by the Mohs Scale of Mineral Hardness, which ranges from 1 (talc), to 10 (diamond). If you pick up a field guide and it doesn't have this basic information, put it back on the shelf and find something else. You can also use online resources to determine the hardness of your material: the most thorough of which I am aware is Mindat, which is currently a free site (although with a free registration you can have access to more features). Even with care taken in selecting which minerals and rocks you tumble, you should still expect for anywhere from a quarter to half of the volume to disappear into your slurry bucket.

Polish is also a consideration: some people will like their stones to have different lustres, so it does come down to individual taste. Personally, I want to see just how brilliantly reflective I can make some materials, so I am experimenting with a range of stone.

Assuming that you are indulging in a basic four week-long process, you will also want to choose your grits with care. Before I'd started working with a tumbler again - after a gap of many years - I had expected that four standard grits made of silicon carbide would be sufficient, and hadn't really understood the importance of the pre-polish and polish phases. I can now tell you that these are crucial (this probably should have been self-evident). The pre-polish and polish phases, both accomplished in my case with very fine aluminium oxide polishes, are essential... if you want your tumbled stone to shine, that is.

Time is also an important variable. Your tumbler should come with a guide, or you can find them on the web with relative ease (also in my last post). On my first attempt through the whole of the process, I allowed at least a week for each tumbling stage. This may have been overkill, but on the other hand, I was recently told of a man who left his rough in the final polish phase for something on the order of six weeks! This is probably unnecessary, at least at first. Follow the guides to begin with, until you will get a sense of which materials will require longer than others in the various stages. Again, this often comes down to personal taste.

One thing that is somewhat annoying is that, for the cleaning phase, the use of Ivory Snow flake detergent is often recommened, at least in North American guides. Unfortunately, this product no longer exists. However, if you can't find another plain, pure, unscented soap, the workaround is simple: find a bar of Ivory Snow soap (which does still exist), or any other basic unscented Castille-type soap (Pure & Natural also comes to mind), and use an old cheese grater to make your own flakes. It may help to dry the soap out a bit first - put it in a warm, dry place for a few days, then grate. You will now have soap ideal for use the cleaning phase of tumbling.

Rock tumbling seems, in the shiny new digital 21st century, like something of an anachronistic pursuit, and perhaps it is. But it is also one which connects us with the realities of making something, of doing something, rather than simply paddling around in the virtual pool. Hopefully, you will take as much enjoyment from it as I am.

Science Gifts Unwrapped: the Rock Tumbler

I haven't done much with a rock tumbler since I was a child, when one of my father's brief enthusiams led him to play with one and to try and interest me in it as well. For whatever reason, I wasn't patient enough to be interested as a child, but, having worked around them and explained them to people for a year and a half, now, I found myself wanting to try one out for myself.

Strangely enough, therefore, one appeared under the tree for me this year, and once the haze of new gifts had worn off, I found myself eager to set the tumbler up and get it going. A little more than a week later, here's what I have to report.

The tumbler that I received, the Lortone Model #33B (Beagle Webstore | Lortone site), features two three pound capacity rubber drums, which are rotated on a direct-drive chassis. The practical result of this is that you can either double your tumbling capacity over the Model #3A, or you can have two batches at two differing stages of polish running at the same time. Not clear yet? Don't worry, it will be.

Set up is a breeze with a tumbler, but it pays to have thought out your tumbling process, just a bit. First thing out of the box, you'll want to have some oil for the bearings on your tumbler. Lortone recommends oiling the bearings (the four points where the spindles intersect with the tumbler housing) before you start, and then once for every thirty days of operation afterwards.

You'll also want to have a space which is sufficiently remote from the rest of your home that the noise won't be distracting. The rubber-barrel direct-drive tumbler is quiet, but it's still audible enough that it won't be something you'll want in your bedroom. Laundry rooms, basements, or garages are the typical sites. Make sure that you have a level surface, like a workbench or table, with easy access to electricity. You'll also want ready access to water. I don't have any taps in the basement, so until I can come up with a better idea that doesn't involve my having to attempt anything resembling plumbing, I've got a number of buckets - for clean water, and rinse water. And remember - although I'm going to say it again later - NEVER put the water / slurry / waste from your tumbled barrels down your home plumbing. EVER. Why? The slurry, when poured out, tends to solidify into something with roughly the consistency of concrete, particularly at bends in the piping. Find another place to pour it out: it's that simple.

While I'm on the subject of slurry, I've heard it claimed that it's possible to reclaim at least some of the grit for re-use after tumbling. I'll have to report back on this, but at the moment, I'm somewhat at a loss to see exactly how that might be done. Perhaps washing it and then pouring the debris off through filter paper? If you've done this, drop your suggestions in the comments, otherwise I'll re-post when I've tried it.

But back to the subject. Now that you've prepared a work area, and oiled your tumbler, it's time to fill the barrel(s) and get weaving. There are plenty of sites out there, as well as books, that cover this. I'd just add that you need to be absolutely certain that your barrel is sealed. If it isn't, and it starts leaking, things can get very messy very quickly, and your batch won't be properly tumbled.

Choose your rough with care, but feel free to experiment. There's no wrong way to tumble rocks and minerals, and the only way to learn what works in each situation is to make a few mistakes. I started with one of the Beagle's batches of high quality tumbling rough, which is turning out to be a great mix of amazonite, tiger's eye, carnelian, chrysoprase, unakite, rose quartz, amethyst, and others, but you can start wherever you like, with whatever you like. I added the rough to the tumbler, then added the coarse silicon carbide grit and water to the appropriate level. Think of grits like sandpapers - beginning coarse, and then increasingly fine. Then start the tumbler.

Rock tumbling takes time. But you knew that already, right? The first cycle, depending on the hardness of the materials, can take between five and ten days. You should really check every day or two, to make certain that you have no leaks, and that you do not have any build-up of pressure in the barrel. Dip out a stone or two just to see how things are going - even after a few days, you should start to see smoothing of the rougher edges. After seven days, I removed the rough in my first barrel, rinsed it, emptied out the slurry, rinsed and dried the barrel, then recharged the barrel and added the next finer round of silicon carbide grit. The rough was already significantly smoothed and shaped. Filled with water, the process continues, with a second new barrel, beginning again with the coarsest grit, this time with a batch of rough corundum, agate, and hessonite garnet.

That's the process so far. Repeat according to directions, and watch your rough turn into attractive, decorative, and interesting tumbled stones. It's easy, if time-consuming, but the results will delight both you and your friends. So try out your new tumbler, and see what treasures you can produce!

There are sites out there to help you, too, as well as books. Rock Tumbling Hobby, and Rock Tumblers for example, both provide some excellent tips and good information. One other thing that they will mention which I must also say again: NEVER put your slurry down your household pipes. Not in the kitchen, the bathroom, the lavatory or directly into the mains drain. Find a place outside instead, preferrably somewhere that you can observe the accumulation over time, to see why this is such an important point. I'll be watching mine with interest (after things thaw, that is).

Happy tumbling!