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Rock Tumbling by Michael Kirk
SNGMS Member & Master of the Tumbler

Hello fellow Rock hounds! I am an avid Rock Tumbler!


I often get asked: “Why don’t my rocks have a shine on them when I am done? Well, there are two reasons:

You rushed the steps.

Grit contamination (meaning some grit from the previous steps was left in there from the previous steps.

The first thing to remember when tumbling is to tumble the correct stones. Stones with pits and grooves will hold grits into the next stages and ruin that stage. The worst kind of stone to tumble is DRUZY Quartz. Don’t do this! The best kind of stone is pretty close to round. Also take into consideration the “MOHS” scale of hardness. Obsidian and Agate do not mix.


The best shines come from the hardest stones. Agate and Jasper are 2 of my favorites. Tumbling Grit is available in a wide range of grades (sizes) and each grade is designated by a number 60/90/220/400/600/etc. Polishing Agents are oxides of metal as reflected in their names: tin oxide, cerium oxide, aluminum oxide, etc. Some polish stones better than others, and if we were running a single type of gem material through our tumbles, we would be wise to select the oxide that works best for it. For my use, I use tin oxide. This works best on Agate and Jasper. Tin Oxide produces a bit higher polish.


**A point to consider before selecting a tumbler is what are you going to do with the gemstone? A 12 lb. barrel will hold about 1,000 stones, if all you want is to make up a little jewelry, a 2-3 lb. barrel should do the trick.


THE FIRST GRIND: fill barrel 2/3 full with stones, add 60/90 grit as directed (depending on your barrel size). ADD 1 tbsp of 20 Mule Team Borax (available @ Walmart laundry soap section) this cushions the water and makes the stones glide over on another easier. I know it sounds crazy, but it works!! Next, add 3-4 TUMS to the barrel. (gas BUILDS UP IN THE TUMBLER And this keeps the gas down, NO joke!!, then add water up to the ¾ line, put the lid on, and give it a shake, and put the tumbler on the rollers. When the stones are tumbling correctly you will hear them stumbling over each other not sliding, the stones should be checked daily. The purpose of the first grind is to remove all the rough surfaces, crevices, blemishes, etc. A normal run in coarse grit is 4-5 days, if not enough material was grinded off, the process stars again. When the stones are at the desired shape, it is time to do the next step. *****WARNING*** DO NOT DUMP THE SLURRY AND ROCKS INTO THE SINK TO BE WASHED!!! YOUR PIPES WILL TURN TO CEMENT! Get a colander and bucket from Home Depot and wash them into the bucket. The next step is to get ready for the next step. After you have rinsed off the stones, put them back into the barrel and wash them. Get some “HE” laundry soap (only HE) and put in the barrel about 1 TBSP, fill ¾ with water and put the lid on and “wash” them. Put then on the rollers and leave running for about ½ hour, after that RINSE stone and barrel out really good, (your stones should smell great).


THE SECOND GRIND After the stones and barrel have been washed out with HE soap and rinsed, put the stone back into the barrel and add 2nd grit (usually 120/220) add 1 TBSP of 20 Mule Team Borax, 3-4 Tums to the barrel and fill ¾ full of water, put the lid on and give it a shake to mix up the grit and put it on the rollers of the machine. Check daily. Leave this run for about 4-5 days. After they have shaped up, (the stones should start to feel smoother), dump out the mixture into the colander and bucket and rinse off. Now put the stones back into the barrel and put 1 TBSP of “HE” laundry soap and fill to about ¾ line and put lid back on and put on rollers. Let wash for about ½ hour, then rinse off.


THE THIRD GRIND Put the stones back into the barrel, and this time you are going to add the 3rd grit 500F (500 fine) be careful with this stuff because it has the consistency of Volcanic ash. ADD 3-4 TUMS and 20 Mule Team Borax as you have done before, but in this stage you are going to add something different. You are going to add ¼ cup of plastic tumbling beads. These cushion the stones in this stage because in the following stages the “slurry” is going to get thinner and thinner, and helps the stone roll off each other. Fill barrel to ¾ full, put lid on and put on rollers. Leave this run for 4-5 days.


THE FOURTH GRIND For this grind you will need 1000 grit AO (Aluminum oxide). This grit is much finer than the 500F and will give you stones a “supercharge” before the polishing stage. After you have rinsed out the barrel and stones in hot water after washing, put the stones in the barrel but add about ½ cup of beads, you will not need 20 Mule Team Borax. Add 1000 grit AO. About ¼ to ½ cup and fill to ¾ with water, put lid on and put on rollers. POLISH When the fourth stage is complete, dump out in colander in bucket, rinse, put back into barrel and beads and stones and fill with 1 TBSP of “HE” laundry soap and wash for about 1 hour. When this is completed, rinse out your stones in hot water and your barrel. Put only the stone back in so that the beads are left behind. Now that the stones are back in a clean barrel, add FRESH beads about ½ cup, add ¼ cup TIN or ALUMINUM Oxide polish. DO NOT ADD 20 Mule Team Borax. Put in enough water to just cover the stones, put lid on and runs this mixture for about 4-5 days.


DONE?? Use 20 Mule Team Borax!! It works!! Use plastic tumbling beads ion stages 3 through polish GOOD LUCK!

Two Great websites for rock tumbling:

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