SirRoxalot
freely admits to licking rocks
Member since October 2003
Posts: 790
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Post by SirRoxalot on Mar 12, 2015 17:19:43 GMT -5
Achieving the perfect polish is a favorite topic of lapidaries of all kinds. We all talk about the special secret recipes needed to get a shine that looks like it's wet, but never define exactly what it is.
I was wondering if there is a tool to actually measure the quality of polish?
A few years ago, having cut a few hundred cabs, I thought I was doing pretty well at polishing. Then I ran into a little old guy at a show, a real master cutter, who showed me some of his double-sided cabochons, and the quality of his polish was so good I never forgot it, and resolved to stay humble.
The local faceting guild had a talk on polishing, and I asked about measuring the polish: how do you know when you're done? These are very meticulous people, and are eternally obsessed with achieving the perfect polish... and they looked blank. All they could say was that you know it when you see it. Problem is, everybody has different levels of experience, and different eyes, and every material seems to polish differently on every type of lap with every type of polishing medium.
I was surprised that, apparently, there's no simple way to measure the quality of polish.
Anybody have any info?
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jamesp
Cave Dweller
Member since October 2012
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Post by jamesp on Mar 12, 2015 17:43:49 GMT -5
The foundation finishes are a bare minimum. 50,000 and 100,000 polish makes a difference. The human eye is a good instrument to judge. Measuring might require an electron microscope to pick up scratches. They do 3-D well.
I knew a man that polished slabs with a 24 inch floor buffing pad that turned motor speed of 1725 RPM. It had a ring around it. He poured slabs in plaster of paris in 6-9 inch rings. He would place the castings in the 24 inch ring and turned it on for a day. It was charged with grit. Ran dry. The small rings rotated in the big ring like planetary gears spinning. Slippage occurred while they rotated around. After a while the rocks were polishing on there own dust. The slabs were getting hit from so many directions. Those were the highest polish I had ever seen.
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Post by snowmom on Mar 12, 2015 17:52:01 GMT -5
The foundation finishes are a bare minimum. 50,000 and 100,000 polish makes a difference. The human eye is a good instrument to judge. Measuring might require an electron microscope to pick up scratches. They do 3-D well. I knew a man that polished slabs with a 24 inch floor buffing pad that turned motor speed of 1725 RPM. It had a ring around it. He poured slabs in plaster of paris in 6-9 inch rings. He would place the castings in the 24 inch ring and turned it on for a day. It was charged with grit. Ran dry. The small rings rotated in the big ring like planetary gears spinning. Slippage occurred while they rotated around. After a while the rocks were polishing on there own dust. The slabs were getting hit from so many directions. Those were the highest polish I had ever seen. Is there no end to human creativity? Wonderful story jamesp!
Regarding how to quantify or specify a level of shine or polish: I would guess that since rock is so inconsistent in itself, with so many kinds, let alone the variations between them, that it would be impossible to devise a precise measure of finish from one cab to another. I know many people photograph their cabs and the camera will pick up things they didn't see. On this forum when we see macro photos or magnified ones, sometimes people will comment that there were things in the photo that they didn't pick up with their eye. So magnification may help refine our perceptions, but I honestly can't think of a way to measure what we accomplish when we polish a rock. Interesting question.
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jamesp
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Member since October 2012
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Post by jamesp on Mar 12, 2015 18:03:28 GMT -5
The ole electron microscope could pull it off snowmom. They show 3-D like no optical scope. Other than that, our eye is pretty good at seeing glare and reflection with it's rapid focus ability.
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stonemaster499
noticing nice landscape pebbles
Member since July 2014
Posts: 97
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Post by stonemaster499 on Mar 12, 2015 18:08:32 GMT -5
glossmeter is used for measuring polished surfaces. I use one for training lapidary professionals how to achieve the best polish - by reflective measure. digital read out. Below is a link to a new one that measures curved surfaces like tumbles. gardco.com/pages/gloss/microwave_scan.cfmor- 10x loupe and learn the scratch pattern of each stage. 100-200x zoom microscope will be more telling at higher mesh stages. comparative sample stones, the ones with the "WOW" polish achieved help guide you there, if ever in doubt and as jamesp says, a sub-micron polish (.5) will take your stones much closer than the standard 1-2 or <2 micron AlOx on the market. i hope this helps.
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Post by snowmom on Mar 12, 2015 18:09:37 GMT -5
jamesp, my eyes have never been good at seeing, I don't trust 'em a bit. I am always amazed at what my crummy camera sees that my eyes don't pick up. I can use all the help I can get. Would be cool if we all could have an electron microscope in our back rooms, huh?
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jamesp
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Member since October 2012
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Post by jamesp on Mar 12, 2015 18:24:17 GMT -5
jamesp, my eyes have never been good at seeing, I don't trust 'em a bit. I am always amazed at what my crummy camera sees that my eyes don't pick up. I can use all the help I can get. Would be cool if we all could have an electron microscope in our back rooms, huh? stonemaster499 is a professional tumbler snowmom. He has a link to a device for measuring polish. $28,000 for base unit, get out the larger pocket book !!
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Post by snowmom on Mar 13, 2015 6:17:14 GMT -5
its awesome they have the tools to do that. It is so far out of my world I could not even conceive of it. Old dogs take longer to learn but they're still teachable. $28K - there must be money in rocks at some level. Glad of the information. thank you!
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tkvancil
fully equipped rock polisher
Member since September 2011
Posts: 1,547
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Post by tkvancil on Mar 13, 2015 8:24:29 GMT -5
All I know is that I'm still looking for the "perfect polish".
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stonemaster499
noticing nice landscape pebbles
Member since July 2014
Posts: 97
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Post by stonemaster499 on Mar 13, 2015 9:57:22 GMT -5
I think mine was $120 in China in 2009. They are about $200-400, but require a flat surface around 60mmx60mm, so not possible with tumbling, but fine for slabs. The link shows new technology for small and curving surfaces, and can measure 20x40mm, which is still on the larger size for a tumble. Sometimes you think you are there or close, but without comparison stones, of the same species, can make an error. The same is true for grading.
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jamesp
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Post by jamesp on Mar 13, 2015 10:44:17 GMT -5
snowmom - Macro shots get it done. I wish my camera had a direct real time connection to the computer screen. tkvancil has $28,000 to spend on a polish analyzer stonemaster499- Never knew such an analyzer existed. Have you ever heard of people tumbling man made ferrosilicon ? It generates a lot of gas. it is Mohs 6 and is some really shiny metallic material. Comes pre crushed in nice tumble sizes. Much of it has bubbles though. Ferrosilicon 75 or 95 has 75 and 95% silica. Ferrosilicon 95 w/2.3 SG. (75% has SG 3.3): Three days in the rotary. But it blew the cap 100 feet in the air when I carefully loosened it:
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stonemaster499
noticing nice landscape pebbles
Member since July 2014
Posts: 97
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Post by stonemaster499 on Mar 13, 2015 10:52:37 GMT -5
jamesp - never seen that before for tumbling. Interesting that releases helium gas. Might be a great product , and turn out like hematite or goethite. Hematite in the market is NOT NATURAL anymore, and is some kind of iron oxide / steel industry waste product. If the cost is good, it could be very interesting; but i can see it sells for $1500-2500 per metric ton ($1.5-2.5/kg). Most rough rocks for tumbling sell at $900-1200 per ton.
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jamesp
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Member since October 2012
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Post by jamesp on Mar 13, 2015 11:29:42 GMT -5
jamesp - never seen that before for tumbling. Interesting that releases helium gas. Might be a great product , and turn out like hematite or goethite. Hematite in the market is NOT NATURAL anymore, and is some kind of iron oxide / steel industry waste product. If the cost is good, it could be very interesting; but i can see it sells for $1500-2500 per metric ton ($1.5-2.5/kg). Most rough rocks for tumbling sell at $900-1200 per ton. I wondered about hematite tumbles being steel waste product. Cast iron can have a lot of silica in particle form and take a fine polish. Yes. Ferrosilicon is expensive. A nice hardness at Mohs 6, but a bit brittle at 95%, thinking 75% would be more durable and still maintain crystal lattice. I believe the after tumble results would look like meteor cross section due to the crystalline structure :
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SirRoxalot
freely admits to licking rocks
Member since October 2003
Posts: 790
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Post by SirRoxalot on Mar 13, 2015 12:24:12 GMT -5
Lol, thread hijack much? ;-)
The gloss meter is intriguing.
Surely the diamond industry has a way of measuring polish. Really, all you have to do is bounce light off it and measure what returns, right?
Lapidary is, after all, but one industry that is polishing highly variable things. Polishing a big telescope mirror used to take a man a year or more. Countertop places have to have standards, industrial polishing of lenses and whatnot is a huge business. Going to have to look into that glossmeter.
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stonemaster499
noticing nice landscape pebbles
Member since July 2014
Posts: 97
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Post by stonemaster499 on Mar 13, 2015 13:08:54 GMT -5
no chance on the iron meteorite. That crystalline structure is unique to that meteor and is used as a means to identify it. For example, your meteor looks to be like Gibeon, which is sold and common in the market - although illegal to export from Namibia.
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jamesp
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Member since October 2012
Posts: 36,563
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Post by jamesp on Mar 13, 2015 13:12:06 GMT -5
Lol, thread hijack much? ;-) The gloss meter is intriguing. Surely the diamond industry has a way of measuring polish. Really, all you have to do is bounce light off it and measure what returns, right? Lapidary is, after all, but one industry that is polishing highly variable things. Polishing a big telescope mirror used to take a man a year or more. Countertop places have to have standards, industrial polishing of lenses and whatnot is a huge business. Going to have to look into that glossmeter. Please forgive the massive hijack. Wandering mind issues. I have looked at videos of polishing telescope mirrors. Glass is tricky stuff. The kits they sell- some have like 8 grit steps. Very gradual steps. Where a vibe can break AO500 into probably 14,000 in a few days. Forces in a vibe are stronger than one might think since they vibrate about 3000/minute. Where hand polishing a mirror is probably not going to break the grit down so efficiently. So the many steps. Measured reflection sounds like a great route. The meter that stonemaster499 mentioned uses reflected microwave radiation gardco.com/pages/gloss/microwave_scan.cfm
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Post by Starguy on Mar 13, 2015 16:51:27 GMT -5
All I know is that I'm still looking for the "perfect polish". tkvancilSirRoxalotYou're exactly right. Every tumble batch I have ever completed had some stones with great polish and some that could have been better. I'm slowly learning to stay away from large flat stones in the tumbler. At least in rotaries, flat surfaces polish well on the edges but can be pretty dull in the center of the flat. Lately I've been grinding a slight dome on flat surfaces. I think that will help. I have about a pound of smaller slabs that I recently rounded off slightly. Will try to post some pictures when they get a little farther along. Great thread.
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SirRoxalot
freely admits to licking rocks
Member since October 2003
Posts: 790
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Post by SirRoxalot on Mar 14, 2015 12:55:08 GMT -5
Flats take twice the time. And you can only have so many in a load. The upside of the extra effort is that when they are finally done, you've got a piece that's ready to be made into a pendant. I've busted up tens of pounds of lower-grade slabs and man oh man do they tumble nicely. Took me a while to realize that I just don't want to cab things like tiger eye and moss agate, so into the tumbler they went. Grinding by hand is a time sink. Do some experimenting. Some stuff can be ready for 220 after a week in a roller in coarse grit. Carbide-tipped tile nippers are awesome for quickly breaking the concave or excessively protruding bits of slab fragments.
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Post by Starguy on Mar 14, 2015 17:28:12 GMT -5
Carbide-tipped tile nippers are awesome for quickly breaking the concave or excessively protruding bits of slab fragments. I like a heavy duty glass cutter for scoring and breaking slabs. They work good on hard agate/jasper. No good for tigereye or jade.
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