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Post by TJ on Oct 5, 2003 15:21:13 GMT -5
I was asked a deceptively simple question whilst manning the tumbling display at our club show yesterday: "What causes the polish?"
As far as I can see, each step is simply removing the scratches left from the previous step, but I'm not sure how that turns a matte surface into a lustrous one. Has anybody anywhere looked at this in depth?
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mrflake
having dreams about rocks
Member since August 2003
Posts: 58
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Post by mrflake on Oct 6, 2003 11:29:11 GMT -5
I am guessing here, but the less scratched a surface is then the more light will bounce directly off it without get caught up in all those indentations, as you know sometimes you have to tilt a stone to different angles to see scratches, presumably it is the shadow or "dark side" caused by light being lost in the scratch that gives it away like I say I am guessing though.
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WilliamC
spending too much on rocks
Member since August 2003
Posts: 416
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Post by WilliamC on Oct 6, 2003 12:39:15 GMT -5
Greetings All, Good question TJ. Basically the polish or more precisely the shine from a polished stone, is a function of the reflectivity versus the scattering of light which is incident on the surface. If a beam of light is scattered from a surface, the photons hitting the surface are re-emmited in more-or-less random directions. If a beam of light is reflected most of the photons hitting the surface are re-emmited with an equal angle from the incident beam. Of course this is just off the top of my head, but any basic physics text will have a more detailed explanation (with diagrams!) of light scattering, reflection, refraction and transmission. But watch out, dig too deep and you'll run into QED, quantum electrodynamics. I just wish I were smart enough to explain it WilliamC
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Post by Original Admin on Oct 7, 2003 3:34:22 GMT -5
Dig even deeper and this strange guy "Schroedinger" will tell you the stone is both polished and unpolished simultaneously, and only when revealed will it have a state which can be determined, or something.
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Djinjuice
starting to shine!
Member since March 2003
Posts: 47
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Post by Djinjuice on Oct 7, 2003 21:14:53 GMT -5
Doesn't polishing create a smooth surface which in turn causes low refraction? Hmmm...
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donwrob
has rocks in the head
Member since June 2003
Posts: 509
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Post by donwrob on Oct 8, 2003 8:22:31 GMT -5
OK, it's been a while since I've given my dormant brain cells a work out like this, I will now attempt to explain quantum electrodynamics: "QED = polishing rocks makes them shiny and purty" There I did it! Aint I sumtin? My depressed mill town HS education has served me well again. Hehe, just having fun guys. It really is an interesting thread, something I just take for granted and don't give a whole lot of thought to. I'll leave the brain work to you guys and just keep loading my tumblers to let QED work it's majic. Let's get ready to TUUUMMMBLE! Later, Don
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Post by TJ on Oct 9, 2003 10:15:32 GMT -5
The plot thickens! A booklet on tumbling describes the process of burnishing: using Ivory flake soap in a brief post-polish tumble to change a cloudy shine into a bright one.
The booklet warned that using any other soap would remove the shine! If it is true that a relatively mild soap or detergent can remove a polish, does it not suggest that there is more to a polish than just a perfectly smooth surface?
Thanks to all that have responded, your input is appreciated. I remain curious!
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donwrob
has rocks in the head
Member since June 2003
Posts: 509
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Post by donwrob on Oct 9, 2003 11:52:39 GMT -5
Very interesting TJ, I have been unable to locate Ivory flake soap in this area for some reason. Instead I use Ivory liquid and it seems to work well for me. I have also used sliced up Ivory bar soap with good results. I believe that docone is a fan of Boraxo soap. I guess there may be some soaps that might chemically react with a given stone and cause some loss of shine, but I don't know of any that do that. I have heard of people using laundry detergent and many other types of soaps all with good results. I also wonder if the term 'burnishing' really applies to rock polishing. To me it refers to a brief melting of a surface to super smooth it and create a high luster shine. An example would be the burnishing of a waxed tile floor. While buffing is simply smoothing the surface to create shine, burnishing actually melts the surface with frictional heating to create a highly polished surface. I still believe that polishing rocks is simply the smoothing of the surface to a point that the majority of light hitting that surface reflects back to ones eyes. I may be way off base here, just my opinion. Thanks for the great thread TJ Talk to you later, Don
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Post by docone31 on Oct 12, 2003 20:54:49 GMT -5
I am going to try to explain what I was shown, however it just might be mental masturXXtion. Thought I would not use colourful metaphors. A stone for the most part is a colloidal mass. Colour is by refraction. I can see the QED formulas but it has been a long strange trip. You have mirror image symatry, refractive index, and percentile light return. A refractive index strive would be a percentile approaching 0. The average formula to be modified is H/W=(P+C)/W+0.02=0.685 P/H= 0.581 C/H= 0.389. That being said, Vol./W^3=0.241. Now that I have confused myself, the tumble process, is a reducing medium. The grits reduce the high points. There is a burnishing, planishing factor. The stone is for the most part stable. Even soaps have little factor except to induce capillary tension to hold the polish grains longer to the stone. The polish points pull off heat impacts, and fractures from internal stresses plane lever. It is a grinding, chipping process. Under the microscope, the smooth surface is quite rough. The roughness, albiet microscopic does not break the ISO ratio as much as unpolished. Since no faceting is involved, the multi fold mirror image symmetry is more random, like polishing a cabachon. Light enters and returns. The reflections are more with the pattern of the stone type. Micro and crypto crystalline patterns will have prismatic types of hues, softer, and distinct. Chrystalline and ortho morphic will be more true to refractive hue. The soaps do not themselves blend with the stone. Borax, my favourite is white, Ivory being a phosphate is white grey. They make the water flow. A wetting agent. Borax doesn't liquifey like phosphate. The oxides, aluminum, tin, cerium, have different grain shapes, and wetting properties. They become a colloid and are compressed by the rotation of the drum and impacts of other stones or particles in the drum. Vibratory is another matter. It is an acceleration of natural wear, and with the oxides, it simulates heat under controlled conditions, or acid etching, as an example. Particles are removed to a plane. I only tumble stones to facet, and I have never really tumbled to use as jewelery as such. The emeralds I have tumbled full cycle never got the shine as a dry polish on my phenolic lap. That requires frictional heat with oxide wear. This is not my speciality, and I confuse myself. I have read reams of information with theories on stelletite layer and amontite layer diffusion, with molecular diffusion tension, and I still have no answer. I think I "know". Basically Occums Razor, the simplest is the answer. The grit smoothes the stones. The more prepared for shiney, the smoother, the finer the grit, the more clarity is visible. I even read theory on how grit is made to multi micron levels. Magnetic shaveing, etc. Has anybody looked at it at depth? I have looked at it from so many ways, I lost the point. Occums Razor. Or as the Architech(sp?) Miers put it, Less is more. I think it wears the stones smooth.
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Post by TJ on Oct 14, 2003 10:22:46 GMT -5
Cool, thanks for ironing it out. The more I think about it, the less likely it is that a detergent would react with most stones. Calcite would react with the harsher detergents, but not the quartz family, unless soaked forever. Easily tested. Just another nugget of false information, or a warning that applies to rubber barrels but not the stones. I continue to be amazed at the lousy information that's out there (not on this board), clearly provided, as one book said, by authors that have never operated a tumbler! Live and learn. Thanks all!
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