jamesp
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Member since October 2012
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Post by jamesp on Jan 27, 2020 11:12:13 GMT -5
Not glare in top pendants with pits from coarse grinding not removed. Lower pendants finish polished well. Both top and bottom have a fine polish. These are glass but rocks behave similarly. Similar damage from 220-500-1000 steps can leave similar damage but such damage is not visible with the naked eye. Poor polish quality is usually caused by this issue and in most cases on the microscopic level.
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jamesp
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Member since October 2012
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Post by jamesp on Jan 27, 2020 11:54:13 GMT -5
Funny thing, rotary tumbling does not make linear scratches when removing/abrading. It removes material by pitting. The abrasive particles must roll like tiny ball bearings leaving a trail of pits behind. Only way I can figure.
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old hound
starting to shine!
Member since August 2018
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Post by old hound on Jan 27, 2020 13:19:39 GMT -5
Thanks James I think you just answered my question about pin holes.
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braat
spending too much on rocks
Member since December 2016
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Post by braat on Jan 27, 2020 14:24:31 GMT -5
jamesp I agree with you...on my one and only glass tumble after stage 3 I saw the pitting shown in your photos ...I had skipped stage 2 as I usually do (did) with normal rock tumbles (didn't see that it made any difference is why). I reran the glass through stages 2, 3 and 4 and they turned out good which made me think all tumbles could maybe be better so now stage 2 is part of the routine for all tumbles... Got another glass tumble in stage 3 right now so we'll see in a few days how they turn out...
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jamesp
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Post by jamesp on Jan 27, 2020 14:58:39 GMT -5
Thanks James I think you just answered my question about pin holes. I have never seen a line scratch on a tumble old hound hound. It is always those pit/pin holes. If you rub to rocks together coated in slurry and grit you will feel the rolling ball bearing effect. A strange way to shape and polish. Happy it may have brought light to your situation.
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jamesp
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Post by jamesp on Jan 27, 2020 15:07:42 GMT -5
jamesp I agree with you...on my one and only glass tumble after stage 3 I saw the pitting shown in your photos ...I had skipped stage 2 as I usually do (did) with normal rock tumbles (didn't see that it made any difference is why). I reran the glass through stages 2, 3 and 4 and they turned out good which made me think all tumbles could maybe be better so now stage 2 is part of the routine for all tumbles... Got another glass tumble in stage 3 right now so we'll see in a few days how they turn out... Glad you have figured this out braat. I attacked this situation a bit different. I went from sic 10/60 to a rotary step using some old SiC 500(substituted for Sic 220) I had laying around. After a week in the SiC 500 it completely removed the pits from the 10/60. Added benefit to the sic 500 was that the glass was ready for AO 200 in the vibe. Still a 4 step tumble, 2 in rotary and 2 in vibe. The SiC 500 made for a quick pre-polish too. Softer stuff like glass has another issue, it does not break grit down as fast as Mohs 7 rocks making it more of a problem in skipping steps.
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old hound
starting to shine!
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Post by old hound on Jan 27, 2020 15:48:47 GMT -5
Thanks you James for explaining the roller effect makes perfect sense. I'll go back to being patient in steed of cutting corners.
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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.
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Post by Benathema on Jan 27, 2020 15:55:36 GMT -5
Softer stuff like glass has another issue, it does not break grit down as fast as Mohs 7 rocks making it more of a problem in skipping steps. Interesting... I would reckon softer stones have a similar issue. A lot of the softer stuff I've tumbled comes out with a finish like you've shown on the top row... that's rotary wet polishing. I get a slightly better finish running it through the dry polish step afterwards, but it still leaves more to be desired. Now I wonder if this medium grit breakdown is part of the problem, or if it's inherent to tumbling softer stones, or ...both...
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jamesp
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Post by jamesp on Jan 27, 2020 16:26:40 GMT -5
Softer stuff like glass has another issue, it does not break grit down as fast as Mohs 7 rocks making it more of a problem in skipping steps. Interesting... I would reckon softer stones have a similar issue. A lot of the softer stuff I've tumbled comes out with a finish like you've shown on the top row... that's rotary wet polishing. I get a slightly better finish running it through the dry polish step afterwards, but it still leaves more to be desired. Now I wonder if this medium grit breakdown is part of the problem, or if it's inherent to tumbling softer stones, or ...both... Sure, soft stones or glass. Soft stones likely get deeper pits(wear faster) Benathema. Can't see why not. Consider that Mohs 7 stones would break silicon carbide down with ease and a super soft Mohs 2 soapstone would take forever break silicon carbide down. That big quartz you rolled should crush silicon carbide like it was brittle salt crystals !
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jamesp
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Member since October 2012
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Post by jamesp on Jan 27, 2020 17:28:19 GMT -5
Thanks you James for explaining the roller effect makes perfect sense. I'll go back to being patient in steed of cutting corners. The ball bearing theory is about the only way those pits can get there. Either way stepping down in grit size is the only way. Bear in mind pits left due to 500 and 1000 are about impossible to see with the human eyes. Even 220 pits can be a challenge to see w/unaided eye. The pits in the photo would have been left by SiC 30.
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EricD
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High in the Mountains
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Post by EricD on Jan 27, 2020 18:48:11 GMT -5
I have some extremely rough, pitted rocks come out every time I load too many of them into the barrel. I always attributed that to the rocks banging into eachother with grit in between. Sort of like trying to smash the grit directly between two rocks, instead of them sliding past eachother. The grit also takes a long, long time to degrade. At least twice normal if not longer.
I do not have this problem when I load it properly to get a sliding-down-a-slope action. In that case they look like they were sanded and are almost smooth when the grit has worn out. Like a 600 grit wet sand on paint type finish
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SirRoxalot
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Post by SirRoxalot on Nov 27, 2020 12:42:01 GMT -5
PITS, not SCRATCHES!!! That is a very, very interesting observation. I’ve seen it often on my failed polishes, but it never clicked. Why on earth are there no scratches? Every other form of lapidary is all about removing scratches! Facetors obsess ad nauseum about cat whisker scratches they observe at 20x marring their perfect polish. Intriguing.
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