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Tumbling sapphires

Posted by Martin Hall  
Martin Hall July 07, 2008 03:44PM
I have a number (some 500g) of rough sapphires that I'd like to tumble polish, and I'd love to get some advice.

The stones range in size from 1g to 15g. They aren't gem quality (of course!) but they are attractive and crystalline, and I think they would look terrific once polished. I attach an example photo.

I'd like to keep their basic shape, so I suppose a vibratory tumbler would be best? I don't have a tumbler of any kind at the moment, so I would appreciate help in choosing a model. Of course I'll practise on other stones first.

My big question is, what to use as grit? Carborundum's not hard enough; what about boron nitride (borazon)? Where would I get a supply of the stuff in various grades?

For what it's worth, I'm in the UK.

Thanks for any help

open | download - sapphires.jpg (9.6 KB)
Johnny July 08, 2008 08:59PM
Only thing is harder then sapphire is diamond. Maybe you can try diamond powder may do it.
TC Reg July 12, 2008 03:49PM
Hi Martin,

Borazon would definitely work, your choice would be based on availability and price as compared to diamond. I have no idea what's available in the UK (I'm in the US), but I'm guessing you could easily order either from an online lapidary, tumbling hobby, or jewelry supplier (or even ebay). A tools or machine shop might carry the borazon cheaper than a jewelry store, tho.

As for tumbling, I like to tumble emerald pieces for the same reason you're interested in the sapphires. Certainly not gem quality, but my nieces & nephews think it's the coolest thing in the world to own a real emerald anyway. Unlike most people who tumble stones, tho, I only use the coarsest shaping grits for a day or so. As you mentioned, many of the pieces have a great shape, and the course grits will smooth them out to look like river stones if you leave them running for long. I just leave them in the course grits long enough to remove the bits of matrix and burred edges. On the other hand, I like to run the polishing grits for a very long time, up to three weeks, I find the extra time gives the best polish for the very hard stones.

"The best tumbler" discussion can take on religious fervor, so I'm not going to start that argument again. :) I suggest you search thru the MinDat archives, and check out a site like Rock Tumblers Hobby ( and read their guides on how to pick a tumbler. (My experience is that cheap ones aren't worth the lower cost.) RTH also has some very good instructions to get you started.

Good luck, let us know how it works out!

Matt Neuzil July 12, 2008 05:05PM
carborundum worked enough to get mine rounded and ready for polish the problem was i only had cerium oxide for polish and it didnt work so right now i got rounded corundums that need polished. I would say that carborundum is fine until you get to finer grits or polish stage.

A buena hambre no hay pan duro
Ray Hill July 13, 2008 11:00AM
doing corundum in a tumbler is a hard thing both on the tumbler and on person doing it , since most media take so very long to make any real grinding and polishing effects on the crystals.. I personally liked the rough xls all the way they looked in the I wouldn't have tried to change them, but that's just me..if you can afford diamond for the polishing, then it is probably the most effective, but the earlier stages might require a more economical man-made boron nitride or something else that is really hard and take the beating that the corundum will give it. If the diamond polishing stages can be done, then you might want some other items put in the mix to carry the diamond grits to the corundums,like rubber blanks or whatever else the tumbler books recommend .
Tim Jokela Jr July 13, 2008 09:17PM
Not many people tumble corundum. If you really want to do it, expect to spend months at it. Why not polish them by hand on a regular cabbing machine or flat lap? Or are they too small?
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