terryb
off to a rocking start
Member since November 2005
Posts: 15
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Post by terryb on Oct 5, 2008 11:21:38 GMT -5
Hello All,
I recently purchased some mixed obsidian (snowflake, sheen, mahogany). I've been tumbling for a couple of years, but have never tumbled obsidian. I know obsidian is softer (5 moh) than jasper and agate. Does anyone have advice or suggestions for tumbling obsidian?
Thanks!
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Post by deb193redux on Oct 5, 2008 21:13:04 GMT -5
After the grind, put in plenty of pellets to cushion.
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rollingstone
starting to spend too much on rocks
Member since July 2009
Posts: 236
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Post by rollingstone on Oct 6, 2008 1:40:17 GMT -5
Here's a link on tumbling snowflake obsidian that might help: forum.rocktumblinghobby.com/index.cgi?board=Pictures&action=display&thread=12375&page=1Basically add a moderate amount of pellets in coarse grind to prevent chipping, then in the other stages add somewhat more pellets than you would use for other stones. The goal is to prevent chipping while not impeding the tumbling action any more than necessary to prevent chipping. A bit of a balancing act. -Don |
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rollingstone
starting to spend too much on rocks
Member since July 2009
Posts: 236
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Post by rollingstone on Oct 6, 2008 1:48:20 GMT -5
Oh, and one other thing. I found that any piece that started out bigger than about 35 grams (1.5 ounces) would end up chipping no matter what (I was using a 6 lb rotary barrel). I tried a few bigger pieces (about 50 grams, 2 ounces), and they kept chipping until I broke them in half.
And if you are breaking up your own rough as I was, then use a hammer and chisel and hit the chisel like you mean business. With a good solid hit on a chisel, obsidian will break cleanly exactly where you want it to. If you don't hit it hard enough, it will just spall off in useless little shards. Safety glasses and long pants a definite must!
-Don
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terryb
off to a rocking start
Member since November 2005
Posts: 15
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Post by terryb on Oct 6, 2008 4:51:44 GMT -5
Thanks for the advice. It looks like plastic pellets are a must. I will probably also try to maintain a thick slurry as well.
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stefan
Cave Dweller 
Member since January 2005
Posts: 14,113
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Post by stefan on Oct 6, 2008 7:49:50 GMT -5
Obsidian is easier than it should be- Like Don said the stuff loves to chip- but I have used larger pieces that were trimmed on a saw- and they don't chip nearly as much- Oh and a nice healthy dose of pellets (I start using pellets from 500 on out)
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Post by Jack, lapidaryrough on Oct 6, 2008 10:15:30 GMT -5
coarse grit should start out at 80 or 100 or finer.
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pebblepup
has rocks in the head
Succor Creek Thunder Egg
Member since July 2008
Posts: 515
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Post by pebblepup on Oct 6, 2008 12:40:49 GMT -5
Thanks for a great post. I have about 100 lbs. of obsidian that I will be working some time this winter. It's good to see some tips to help when I get to it.
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