unc2three
off to a rocking start
Member since August 2017
Posts: 8 
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Post by unc2three on Sept 9, 2017 11:39:05 GMT -5
Hey everyone, I'm new to the board and new to polishing geode slabs in general. I have done lot of research on how to do it etc. I can't really afford a lapidary machine so I started with a car buffing hand rotary machine. The slabs I bought were already cut and were already very smooth with slight saw marks. I attached 600 grit sandpaper to the wheel and sanded for about 10-15 minutes. I then went to 800 grit and it was starting to get shiny, the edges are polished perfectly but I'm not getting the shiny polish look all over the rock, just the edges. I then used 1200 grit and it was a little better. But I don't understand why the edges are polished and the rest of the rock isn't. The slab is flat and even with the polishing wheel so it's not favoring the edges. Any help is appreciated. Thanks
Chad
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minerken
Cave Dweller 
Member since August 2013
Posts: 466
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Post by minerken on Sept 9, 2017 12:44:45 GMT -5
I would say you are starting off with too small a grit try going with an 80 or 100 grit and a fairly flexable backing disk then move to like a 220,400,600 grit progression and a final polish with a polishing powder like cerium oxide, tin oxide, or one of the other polishing compounds.As for your slabs being totally flat I doubt it they may look that way but hundredths of an inch will make a difference.
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unc2three
off to a rocking start
Member since August 2017
Posts: 8
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Post by unc2three on Sept 9, 2017 12:57:09 GMT -5
I would say you are starting off with too small a grit try going with an 80 or 100 grit and a fairly flexable backing disk then move to like a 220,400,600 grit progression and a final polish with a polishing powder like cerium oxide, tin oxide, or one of the other polishing compounds.As for your slabs being totally flat I doubt it they may look that way but hundredths of an inch will make a difference. Thanks for the info Minerken, I will try starting over with the harder grit, thanks for the help |
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Post by pauls on Sept 9, 2017 16:31:46 GMT -5
A flat slab and a rotating buff seems to always polish on the edges, just one of those things, use near the edges of the buff angled a bit to get in the centre.
A good alternative is go a bit caveman, grab a flat piece of steel, bigger than your slab, 1/8 inch or so thick will do. Sprinkle with Silicon Carbide grit, about 100 grit, just a sprinkle, a sprinkle of water and start rubbing your rock around the steel. Keep going until the whole slab is the same mat finish with no marks left from the saw.
Wash everything well and move to a finer grit, 240 grit, same deal, you will see the mat finish change to a finer finish very quickly. Wash and change to fine grit, 600 grit. You can go to finer, say 1000 grit but you should be able to get a polish after 600 if you keep rubbing it around in circles until the grit has broken down to really fine.
After those grit stages I normally just polish with a felt buff and tin oxide (damp only)
This method is really quite quick, I use it to polish the flat backs of cabochons because of the same problems and can do the back of a cab in 10 minutes or so.
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unc2three
off to a rocking start
Member since August 2017
Posts: 8
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Post by unc2three on Sept 10, 2017 5:59:18 GMT -5
Thanks for info Pauls. I tried looking for cerium oxide Compound polish and tin oxide but can't seem to find it locally. I looked at Lowe's and they said they don't have it. Any idea where I could find some? Or is it a specialty thing I need to get online?
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Post by manofglass on Sept 10, 2017 8:27:21 GMT -5
Therockshed.com or
Covington engineering.com
Kingsleynorth.com
They all have polish
Walt
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Deleted
Deleted Member
Member since January 1970
Posts: 0
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Post by Deleted on Sept 10, 2017 11:12:40 GMT -5
Try drawing on the surface with a colored pencil. Lots of lines zigzagging all over the surface.
Now
Put it back on the lap. If it's flat the pencil will disappear from the entire stone in a few minutes. If not all gone evenly, stone ain't flat.
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