Are you thinking about using a rock tumbler? Do you want to create beautifully polished rocks in a multitude of colors? Rock tumbling is a cool and fun hobby that promotes learning of geology. Despite how cool it is to open tumblers and view all the polished stones however, you should know that this is not a quick and easy process.
If you’re thinking about buying a rock tumbler as a hobby, here’s what you need to know:
There Are Actually Two Types of Tumblers
First off, you should know that there are two types of tumblers in the market today. The first one is the rotary tumbler and is the most common one in the market today. As the name suggests, this rotary tumbler works through continuous rotation of the barrel. The rocks inside smash against each other, polishing the surface and allowing the smooth color to come out.
The second version is called the vibratory tumbler which just shakes and vibrates to promote friction for polishing. Of these two, the rotary tumbler usually takes longer to produce the smoothened stones because of the different stages you need to go through as well as the various grit types that need to be used. Of course, it’s perfectly possible to use both types, one after the other, in order to speed up the process.
Factors Affecting Tumbling Time of Stone
Type of Tumbler
Rotary tumblers usually take a total of 4 weeks to produce the polished stones. The first stage takes seven days and using the heaviest or coarse grind followed by another seven days of medium grind. The third week is a fine grind until eventually, you get to the final polishing stage.
With each stage, you throw out the garbage, put in a new grit material and allow the barrel to do its job without disturbing the contents. Some enthusiasts would sometimes extend the process by repeating a grind, especially if they’re not happy with what they got.
A vibratory tumbler however manages to cut that time cleanly in half. You also skip the coarse grit and go directly to a medium grit for 24 hours or until you’re happy with how the rocks look. You then follow this up with the fine grit and then the polishing grit for 3 days each. Check and repeat as needed.
What if you use both the rotary and vibratory tumbler to speed up the process? Indeed, this will speed up the stages further without reducing the quality of the stone you come up with. The rotary tumbler would be used with a coarse grind for 7 days before moving it to the vibratory tumbler. The vibratory tumbler would be responsible for the medium, fine, and polishing grit, all three taking one week or less. This will produce beautifully polished stones that would look better than the stones you get if you only use a vibratory tumbler type.
So why not just use the vibratory tumbler to really get fast results? There are two main reasons for this. The first one is that a vibratory tumbler is much more expensive. It costs more than 50 percent of the rotary tumbler which can be off-putting for complete beginners. The second reason is that vibratory tumblers do not create rounded stones. It smoothens out the surface, but if you want a softly rounded look, the vibrator type would not be a good choice.
Hardness of the Rock
The hardness of the rock will also determine how long it would stay in the tumbler for you to produce a smooth finish. Harder rocks like quartz, agate, and jasper may need all of four weeks or more inside a rotary tumbler. The likes of marble, fluorite, and calcite however, are integrally softer may need only a short period of time inside the rotary.
As a rule of thumb, anything with a hardness of 3 in the Mohs scale would need only 3 days to smoothen out. For those that are between 4 to 5.5 in the scale, 4 to 5 days of rounding would be perfect. Anything beyond that however would need the full 7 days to create the rounded curves. Note however that when we talk about rounding rocks based on their hardness, we are only referring to the course grind. Hence, a stone with a hardness of 3 only need to be on the coarse grind for 3 days. After that, you can follow up with the medium grind, the fine grind, and the polishing grind – all for the requisite period of 7 days each.
If you’re picking up stones from the wild and not sure where it places in the hardness scale, try using common objects as a reference. For example, a fingernail has a hardness of 2.5 so if you can scratch the stone with your fingernail, that means that it is softer than your nail. A copper penny is 3.5, a knife is 5.5, an ordinary steel nail is 6.5, and a drill bit us 8.5. Have these small things handy when checking stones and you should be able to tell which stones will take longer to tumble.
Understand that when rock tumbling, the rocks should be the same level of hardness, otherwise they might scratch each other inside the barrel. If this happens, you’ll ruin the end result of the rocks which can be disappointing.
Sizing of the Rocks and the Tumbler
Remember that the polishing action comes primarily from the friction you get between the rocks and grit you put inside. If the rocks are too big in relation to the barrel, it would take a longer time to finish it completely. The same is true if you load the tumbler with too many rocks. You’d think that when loaded with rocks, there would be more “friction”, but that’s not the case at all. You want there to be enough space in between for the sanded part to float in.
So how big should the rock be? Ideally, it should not be more than 50 percent of the diameter of the barrel. This guarantees that there’s enough tumbling space in there to create friction. As for the volume of the barrel, make sure to fill it only up to ¾ with rocks. Put in just enough water to fill the spaces between the rocks, making sure that it doesn’t go above the topmost portion. Finally, add in the grit, lock the tumbler and allow it to work.
The Integrity of the Rocks
When we say “integrity” of the rock, we’re talking about the likelihood of it fracturing in the middle of the stage. Even before putting the rocks inside the rotary tumbler, you should make sure that the rock itself looks solid with zero chances of breaking up inside the barrel.
Checking in Between Intervals
Keep in mind that checking the stones between each step is important if you don’t want to accidentally lengthen the smoothing out process. Check for fractured and pitted stones which look like they could break up when allowed to go through the tumbling process. This is because these small portions can break off and ruin the other stones – especially if you’re already using a medium, fine, or polishing grit. Pitted stones can also capture the smaller grit particles and therefore prevent them from rotating and polishing the area.
With each tumble, do a thorough inspection and discard the stones that will not give you the results you want. Otherwise, you might have to repeat the process which will take longer.
Can You Skip Stages?
Some enthusiasts want to see results quickly so they choose to skip certain stages or perhaps try to extend one stage and skip another. For example, there are those who would go directly to polishing grit after using medium grit, therefore bypassing the fine grit.
Understand that while this possible, the results may not always be as expected. There’s a reason why there’s a process for rock tumbling that has to be followed – even by serious enthusiasts. Each grit type has a particular purpose and by skipping one in favor of another, you might scratch the surface and produce unpolished stones no better than the ones you find on the road.
Of course, some enthusiasts will tell you that it’s possible to skip steps with certain stones. However, this is a trial-and-error technique that allows you to learn as you go. After some time with rock tumbling, you should be able to judge what to do next with the rock you got and thereby shorten the tumbling time as you understand the nature of the rock and the grits used.
To wrap it up, there’s no fixed or perfect time for rock tumbling. No matter how excited you might be to open that barrel and find amazingly colored stones, the fact is that good results take time. Hence, be patient and continue to learn about rock tumbling so that you can put your own spin on things and perhaps develop a technique that will let you get faster results without diminishing the quality of the polished rocks.