mrhomescientist
having dreams about rocks
Member since October 2019
Posts: 51
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Post by mrhomescientist on May 14, 2020 14:00:36 GMT -5
I'm working on tumbling some labradorite rough I bought from the Rock Shed, and from what I've read around here it's pretty tough to get right. I'm using the procedure from this thread: forum.rocktumblinghobby.com/thread/36957I'm using 3lb tumbler barrels. I first put the rough stones in with my usual stage 1: 3 tbsp of 60/90 SiC, for one week. (This was before I read that thread recommending no grit; I've got one of those running right now.) This smoothed them out nicely for the most part, though I had to run a couple weeks on a few of them. Once I got enough for stage 2, I followed the advice of the thread and loaded it up with plastic pellets. I used more grit than he did, though, at 2 tbsp of #220. Here's the barrel before adding the grit: Here's what they look like after 1 week: Some observations: The labradorite actually feels more rough than when I put it in! It's very strange. It looks like the pellets have "absorbed" the grit - that gray won't wipe off. Interestingly, the grit leftover in the rinse water looked almost as good as new. I could see a lot of sparkling grit particles instead of the usual dull mud I see at the end of a run. Hypothesis: Maybe I used too many plastic pellets? I wanted to cushion the stones as suggested, but they may have been too cushioned to grind against the grit. Any suggestions on how to proceed from here?
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pizzano
Cave Dweller
Member since February 2018
Posts: 1,390
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Post by pizzano on May 14, 2020 14:39:04 GMT -5
Lab is tricky.......
Rock buddies I know who rotary tumbled this material started out using 120/220 silicon carbide (not a 60/90) with a mix of smaller like hardness material (no pellets or ceramics). The smaller material helps provide volume and surface contact as the slurry develops.
Once they've gotten the shaping/rounding they desire, most success completing to a polish has been done in a Vibe type tumbler with small (previously used) ceramics.....using a 500 Alum Oxide, then an Alum Oxide pre-polish (1000 or higher), then a high end polish compound or Cerium Oxide.........this material is difficult to achieve a "fracture" free polish in a vibe and even more difficult in a rotary.....but it can be done.
The link.....:
will help, but the attention to detail is lacking some.......this material takes considerable baby-sitting......no two batches will have the same outcomes.
With a little experience and patients, you'll get there.......not suggested as a material for 1st timers....!
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Post by miket on May 14, 2020 15:10:04 GMT -5
I tried it once and failed miserably. I had a cab that I made, ran it in the rotary for about a week in coarse then in the vibe for a week to finish. Keep us posted on how you turn out, I like Labradorite- and good luck!
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Post by pauls on May 14, 2020 21:33:53 GMT -5
I think you are doing OK with a difficult material. You probably overdosed with grit but that's not a deal breaker. The pellets would have cushioned the grit from breaking down. Clean them up, and move them on to the next grit, new pellets though.
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JBe
starting to spend too much on rocks
Member since January 2019
Posts: 103
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Post by JBe on May 15, 2020 11:42:26 GMT -5
Thanks for posting this! I have a pile of lab I've been accumulating until I have enough for a dedicated batch and would love to be able to learn from other peoples' experiences with it.
I've tried plastic pellets before and had them stain/absorb grit as well. I kept separate pellets for each grit stage just to be safe.
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Post by pauls on May 15, 2020 21:37:50 GMT -5
That sounds good JBe. I have tumbled a few different types of Feldspar to clean them up. I facet so looking for nice clean flaw free material, this doesn't get the luxury treatment of my good rocks just enough to polish so I can see inside, it does take a good polish if you can stop it fracturing along cleavage planes. It facets really nicely too, our Labradorite here in Australia is just a nice clear honey colour, no blue schiller, so perfect for faceting.
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