docharber
has rocks in the head
Member since October 2008
Posts: 693
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Post by docharber on Apr 17, 2012 21:15:31 GMT -5
Our club is clearing out the estate of a veteran collector and lapidary enthusiast. There were several cans of abrasive powder, presumably suitable for tumbling, made by MDC Industries of Philadelphia. i can't google the manufacturer and I presume they are out of business. Thiss stuff, specifically, is labelled with a muyltipurpose label with fields filled in by hand. The "NO." field has VSED written on it, and then printed "MICRO GRAIN PRECISION ABRASIVE POWDER" followed by another blank field with "MGP-II (versus 11) Levigated Alumina " handwritten on it. Is anyone familiar with this stuff?? there were several cans and we bought them all at the sale, bt aren't sure they are suitable for our purposes as a polish. thanks,
Mark H.
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Minnesota Daniel
freely admits to licking rocks
A COUPLE LAKERS
Member since August 2011
Posts: 891
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Post by Minnesota Daniel on Apr 18, 2012 0:51:15 GMT -5
Levigated Alumina is air classified (sorted with an airstream somehow) calcined alumina that is 3-5 microns in size. So... what you have is graded 4,000 to 8,000 grit calcined alumina -- might be used as pre-polish, more likely polish.
Fused Alumina is less pure than calcined alumina, is composed of larger, blockier crystals, and comes in sizes from 5 to 70 microns (3,000 to 300 grit). Fused alumina is used for pre-polish.
Sub-micron aluminum oxide is monocrystalline or polycrystalline calcined alumina. This is fine polish. Linde A is .3 microns, for example.
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Post by johnjsgems on Apr 18, 2012 8:46:30 GMT -5
Mark, you can try it and see how it works. TXP and other "tumbling grade aluminum" are generally 3-4 micron and work great in rotary tumblers and on buffs for harder stones. I believe somebody (Graves?) sells "levigated Alumina" as a pre polish. I've heard of the term levigated over the years but Daniel provided the first explanation I've heard. If they had a "II" they likely had a "I" also so likely had different grades for different purposes. Load a buff or tumbler and see how well it works.
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docharber
has rocks in the head
Member since October 2008
Posts: 693
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Post by docharber on Apr 18, 2012 14:24:41 GMT -5
Thanks, guys. I;ll try it out and see. I looked up levigated and the definition also included sorting the grains through a wet grrinding or slurry based process. i don't exactly get it. I was thinking the "II" might also be micron size but I think that's unlikely. I have a lot of this stuff to play with. i have used Kingsley North Micro-Alumina polish and it works great. I was hoping this would be similar.
Mark H.
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Minnesota Daniel
freely admits to licking rocks
A COUPLE LAKERS
Member since August 2011
Posts: 891
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Post by Minnesota Daniel on Apr 18, 2012 15:36:34 GMT -5
MGP-II could mean anything really. I think the more important factor with alumina is that calcined (which includes levigated) is purer than fused, and is also flat crystals vs the blockier crystals of fused alumina. The size of the grains I suspect is less important because if you just leave the the rocks to tumble long enough, the grains break down to eventually become sub-micron anyway.
The wet grading process that involves a slurry I think is for alumina that is sold as a wet slurry for lapping metals.
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