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Post by knave on Feb 22, 2020 21:26:27 GMT -5
I’m curious. Why is it ok to use ceramic with obsidian, but otherwise it is discouraged to mix different mohs rocks?
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shardy
starting to spend too much on rocks
Member since October 2019
Posts: 110
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Post by shardy on Feb 22, 2020 21:31:12 GMT -5
My thought is that it's most important during coarse grinding due to the sharp edges of the harder rock rather than just the hardness itself. But I know very little.
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Post by rmf on Feb 22, 2020 21:38:39 GMT -5
Soft stones grind faster than hard stones so if you tumble them together the soft ones grind to much away. then if you finish them together the harder/tuffer stones ping away at the polish on the softer stones preventing them from taking a good polish. Ceramic pellets are approximately the same hardness as obsidian.
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Deleted
Deleted Member
Member since January 1970
Posts: 0
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Post by Deleted on Feb 22, 2020 21:44:22 GMT -5
I'm not a regular tumbler, but I'll throw in that it would be the same reason that it usually works best to use hard wheels, laps, and polishing disks when finishing mixed-hardness material (i.e., because those made of softer material tend to push the grit/polish down more into those areas of the stone that have weaker/softer hardness, producing undercutting).
Probably depends on the obsidian, though. Some of it is fairly uniform, but in others there are oxide inclusion layers/features that form softer areas (which can look duller than the surrounding obsidian - at least when cabbing or carving - a result that can be minimized by doing at least the polishing stages on wood, hard leather, etc.). Just guessing that is the reason, though. But hey, whatever works!
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Post by knave on Feb 22, 2020 22:11:58 GMT -5
I thought ceramic pellets were mohs 8+?
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Post by knave on Feb 22, 2020 22:13:53 GMT -5
Hmm. I had a little trouble in this last loto load. But I just remembered. I threw in some unconditioned pellets..... kinda just winging it and hoping it would all be fine. Sure enough little ceramic shaped digger inclusions on the otherwise smooth surfaces. Bah.
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Post by joshuamcduffie on Feb 22, 2020 22:17:22 GMT -5
It’s hardness is 7+
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Benathema
has rocks in the head
God chased me down and made sure I knew He was real June 20, 2022. I've been on a Divine Mission.
Member since November 2019
Posts: 703
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Post by Benathema on Feb 22, 2020 22:38:55 GMT -5
I'm borderline convinced these "rules" for mixing stem from the manuals, getting passed down over and over, and probably aren't as important as we make them out to be.
I can throw a chunk of granite, or granite pegmatite, in the barrel and get a high gloss on the quartz spots, and lower gloss on the feldspar, and both are in the same rock. Other quartz chunks get a high gloss, other softies get the lesser gloss, in the same barrel. Mix or keep them separate, the results are the same. For real, barrel of quartz is all high gloss. Barrel of feldspar is all low gloss. Seems to me the prepolish/polish choices make the biggest difference. Soft stuff can go into dry polish to improve the finish a bit.
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Post by knave on Feb 26, 2020 10:39:27 GMT -5
I have ceramic from Shawn at the rock shed. They do not wear quickly at all. Does anyone here know what they are made of? Compressed AO? Porcelain?
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Post by joshuamcduffie on Feb 26, 2020 10:58:37 GMT -5
I've never heard of ceramic being discouraged with different Mohs scale rocks. I know that Obsadian and Quartz are known to "bruise" in a rotary tumbler, hence the recommendation to cushion them. The nonabrasive ceramic media are made of porcelain.
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Post by knave on Feb 26, 2020 11:02:38 GMT -5
Maybe you’re not understanding what I’m asking. What’s the difference between mohs7 porcelain and mohs 7 agate that makes one acceptable to run with obsidian and the other not?
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Post by knave on Feb 26, 2020 11:16:27 GMT -5
Maybe you’re not understanding what I’m asking. What’s the difference between mohs7 porcelain and mohs 7 agate that makes one acceptable to run with obsidian and the other not? One difference would be the agate could have sharp edges in rough tumbling. We have a member who posted excellent obsidian run with polished quartz.
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Deleted
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Post by Deleted on Feb 26, 2020 12:09:46 GMT -5
One difference would be the agate could have sharp edges in rough tumbling. My thought, too. What you are trying to avoid is points of other rocks in your load pushing into softer sections of other rocks in the load - whether that be edges from harder material (producing gouges), or soft stuff that can deform and push the grit into (and undercutting) portions of other rocks. The porcelain beads or pellets don't deform, while providing cushioning as the grit does its work. Obsidian, as is also the case with other materials, is very often not of uniform hardness. Looks to be different shapes of porcelain media for different purposes, too. The beads and round pellets roll with the tumbling action, while the more angular shapes are supposed to work better for rounding off. Anyone recall any threads here about various tumbling media types and shapes?
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