jimgsmith
starting to shine!
Member since September 2022
Posts: 37
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Post by jimgsmith on Dec 24, 2022 11:17:23 GMT -5
I made the mistake of tumbling a batch of Gabbro, and the results were...not great. So I'm wondering if there is a recipe for tackling rocks which are composed of multiple minerals, with a significant difference in hardness like Gabbro, Granite or Diorite. Using the "standard" recipe results in beautifully smooth rocks after stage 1, but then stages 2-4 in the vibe results in undercutting and the rocks end up partly polished, partly undercut and completely underwhelming. I have heard of dry tumbling, as well as using additives like psyllium fiber, etc, but just wondering if there is a recipe that generally works for these types of rocks.
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stefan
Cave Dweller
Member since January 2005
Posts: 14,113
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Post by stefan on Dec 24, 2022 11:35:41 GMT -5
Honestly your results will never be the typical super shine we all come to expect. I have some luck with granite (fine grain) but if you look closely you can see the undercut pits. The problem isn't the softer minerals, it's the harder stuff that does not grind fast enough lol. You can try tumbling in a rotary and may see slightly better results than with a vibe. Some rocks just don't seem to want to polish despite the best efforts.
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ataraktos
starting to spend too much on rocks
Member since January 2020
Posts: 140
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Post by ataraktos on Dec 28, 2022 16:08:04 GMT -5
You can check out the "crystal wisdom with Shannon" YouTube. She does crystal mediation videos now but for a good while she also had a "rock tumbling weekly" series (which I really miss!). On episode 21, she had some IG a bit along in the process, so a few episodes back, you can find her starting the gabro and watch from the beginning to end. Hopefully you find something that helps a bit.
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jimgsmith
starting to shine!
Member since September 2022
Posts: 37
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Post by jimgsmith on Dec 28, 2022 22:06:44 GMT -5
Thanks for the tips! I watched some of her videos, and she seems to be using rotary tumblers only, and a lot of ceramic media. Like a lot, a lot! So the common thread from both of you is to try the rotary instead of the vibe, and it looks like the more the media the better. So I’ll give that a shot and see how I do. I know Gabbro is a challenging stone to polish, but it’s beautiful and I think it will be worth it.
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jimgsmith
starting to shine!
Member since September 2022
Posts: 37
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Post by jimgsmith on Dec 30, 2022 9:46:49 GMT -5
Lots of ceramic cylinders in a rotary seems like the best strategy to me too. I don't know anything but it's my hypothesis that if you never poke the softer minerals with an acute angle and always touch them at the level of the harder minerals, you should be able to minimize the undercutting, probably not prevent it completely tho. I think the cylinder shape in rotary would be best at applying pressure without poking the stone. Angled cylinders might be fine too or a step in the wrong direction, if media shape matters at all. Then again, maybe that's all wrong. I have some granodiorite or something like that that I tried to polish on my flat lap and applying the same hypothesis it should have polished the stone by touching everything evenly. But this wasn't the case. The softer minerals, mica maybe?, seem to snag on a diamond and flake off or something. Somehow it still undercut even on a flat lap. I thought the vibe had more gentle action, and would yield better results for soft or delicate stones, so the suggestions to use a rotary surprises me. Can anyone explain why a rotary would be more gentle than a vibe?
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waterboysh
spending too much on rocks
Member since April 2021
Posts: 386
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Post by waterboysh on Dec 30, 2022 10:16:26 GMT -5
I thought the vibe had more gentle action, and would yield better results for soft or delicate stones, so the suggestions to use a rotary surprises me. Can anyone explain why a rotary would be more gentle than a vibe? I'm curious too but I had a similar experience. I just could not get a super great shine on the Apache tears I was running in the Lot-O. They would come out pretty good but when you looked closer there was a slight haze to them. After trying several times I ran them in my 3lb rotary barrel with quartz pea gravel as the media instead of ceramic and they came out super good. I just chalked it up to obsidian being more brittle.
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