Lapidary Fundamentals: Gemstone Tumbling

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Lapidary Fundamentals: Gemstone Tumbling

Postby PinkDiamond » Thu May 10, 2018 11:22 pm

I have a small tumbler I got decades ago that's in a closet somewhere around here. I haven't used it for so long because it's a cheap model that makes quite a racket to be running as long as tumblers need to run, and you'd think that the directions that come with a machine would be all you'd need to know, but there's some important information in this article that I was totally unaware of, so I'm posting it for you because there may be tips you can pick up from it, too. By Don Clark, from the Gem society, hope you find a few tips you can use in it. :)

Lapidary Fundamentals: Gemstone Tumbling
by Donald Clark, CSM IMG
Step 1: Introduction to Gemology

Lesson 14

Gemstone tumbling can bring out a beautiful polish in many hard gems. “Agates,” tumbled polished, Minnesota, by Paul VanDerWerf is licensed under CC By 2.0

"The simplest (and least expensive) lapidary art form to learn is gemstone polishing. The only equipment you need is a tumbler and abrasives, often sold in kits, and the rough you want to polish. The only skills you need to start is the ability to read instructions and measure the abrasives. Nevertheless, before you buy your first gem tumbler, there are a few important factors to bear in mind.

Gemstone Tumbling: Preliminary Considerations
Stone Sizes

In order for the tumbling action to work, you must place stones of various sizes in the revolving barrel. They need to range from not more than half the diameter of your barrel to about 1/10th the size of the largest stone. You cannot simply put a few large pieces in the tumbling barrel and expect them to come out nice.

Simply gathering stones in an assortment of sizes isn’t too challenging. If all the sizes you need aren’t readily available, simply use a hammer to create them. However, if you intend to work with stones the size of melons, you’d better be prepared to gather a lot of filler!

Gemstone tumbling simulates the conditions that weather rocks in a stream or at a beach, only greatly accelerated. “Tumbling” by pfly is licensed under CC By-SA 2.0

Tumbler Size

Knowing what you want to polish and the size range of the stones you need will help you determine what size tumbler to buy. The largest stone you can finish will be about half the diameter of the barrel. Therefore, your least expensive models with a barrel four inches in diameter can only finish two-inch diameter stones. Moving up to a machine twice that size will cost twice as much and require twice the abrasives and filler. For the serious lapidary, this is a reasonable investment. For the part-time hobbyist, it may not be worthwhile.

Consider how often you plan on using your machine. For example, if you just want to polish a couple of dozen agates you found on vacation, you might not need a machine large enough to do them all at once. With a smaller tumbler, you may have to process your stones in two or more batches. However, if the gem tumbling machine is going to sit idle most of the time, purchasing a larger unit would be a waste of money.

“Tumbled Agate and Jasper,” tumble-polished gems inside a 15-pound rock tumbler barrel, by 88pathoffroad is licensed under CC By-SA 3.0

Gemstone Hardness

All the gemstones in your barrel need to have the same hardness. Harder stones will scratch softer ones. If you have even one stone in your tumbler that’s harder than the rest, it will scratch everything else in the barrel. (Of course, stones used just for filler can be softer that the gems you want to polish, since it doesn’t matter if they’re scratched).

Measuring the hardness of your rocks may seem daunting but can be accomplished with simple tools. A pocketknife is about 6 to 6.5 in hardness. A file is closer to 7. You can also assemble a set of stones of known hardness value for your testing.

Materials of the same hardness won’t scratch each other. Therefore, you can use one stone to test rough of the same kind. For example, if you want to tumble some agate pieces, use one to scratch the others. The piece shouldn’t scratch any of them or show any wear itself. If it does wear away on a stone, that piece is harder and shouldn’t be included in your tumbler.

Not all stones will take a polish, just the harder ones. A simple field test will save you from bringing home a lot of useless rock. Try scratching them with a pocketknife. If you cannot scratch the specimen, it will take a polish. You will find other potential prizes are nothing more than compressed mud. Not only will they not take a polish, they’ll create quite a mess!


Location, location, location. That saying isn’t just for real estate. You need to consider carefully where you’re going to place your equipment. Gemstone tumbling machines are noisy and run 24 hours for days on end. Lortone makes tumblers with rubber barrels to minimize the noise. While this helps, they’re still noisy. You need more than one wall between your bed and the tumbler if you want to get any sleep. If you’re using a machine with a steel barrel, you’ll need more than that! Don’t forget about your neighbors, either. Simply putting the tumbler in the garage may help you sleep but won’t ingratiate you with them.

If you don’t have a secluded room or basement, consider making a container for it. A cardboard box lined with styrofoam or covered with an old blanket will reduce the sound considerably.

Choosing A Gemstone Tumbling Machine

There are two kinds of tumblers: rotary and vibratory. Rotary tumblers are the most well known. They can be found at any rock shop, scientific supply house, toy store, and, of course, online. They’re the least expensive variety and come in the widest range of sizes.

Vibratory tumblers shake the ingredients, rather than rolling them over each other. They have the single advantage of being faster. What would take weeks in a rotary tumbler can be done in a couple of days in a vibratory. They also have a significant disadvantage. ... " ... icrography
ISG Registered Gemologist

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((¸¸.·´ ..·´ There are miracles left for you to do .... -:¦:- -:¦:-
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Re: Lapidary Fundamentals: Gemstone Tumbling

Postby SwordfishMining » Mon Nov 25, 2019 3:39 am

I found a world of help on the forum Rock Tumbling Hobby dot com also.

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