Sanding slate

I have used the reverse side of some slate tiles for a window-sill, thinking I could easily remove the marks left by the commercial slate cutter (very shallow, less than 0.2mm at worst, circular scratches, can't even feel most of them with my finger nail). Being slate, a soft stone, I thought I would have no problem.
Oh boy - I've tried using polishing agents like Brasso (left a horrible mess), sandpaper, wet and dry, high and low speed sanding attachments, an aluminium oxide sanding disk and lastly an angle-grinder mounted high speed flap wheel. All to virtually no avail.
Has the cutting process hardened the surface of the tiles in some way ? Does anyone have any ideas of what else I can try ? I've heard of something called carborundum paper but never seen any (and B&Q have never heard of it) - anyone know anything about this ?
Cheers
Stephen
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On Wed, 20 Aug 2003 13:47:47 -0700, "Stephen Judge"

For your "Carborundum", try "silicon carbide". The black stuff commonly sold as wet and dry. It's harder than aluminium oxide and more appropriate to stonework.
One of your biggest problems will be dust. Unlike wood, stone dust doesn't compress and so the paper will tend to clog. Keep a vacuum running as a dust extractor, just to keep the abrasive cutting. Working it sopping wet will help too.
http://www.csmabrasives.co.uk /
Ignore the impossible web site, get a paper catalogue. They sell everything you could ever want.
For a quick fix from the local DIY shed, try the bright orange Plasplugs tile-fitting tools and get a "tile file" - a grit-covered latticework. This is a carbide abrasive on an openwork substrate and good for working dusty stone.
What colour is the slate ? The Chinese stuff is quite soft (but variable - red / brown is softer), fresh Welsh grey / purple is hard, and green Lakeland slate is very tough going.
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It seemed a good idea at the time to use the reverse side of some unhoned slate tiles to get a smooth surface on a window sill. This was thinking I could easily sand out the cutting marks left on the surface.
I've tried sandpaper, glasspaper, high speed, low speed, by hand, with and without water, aluminium oxide disk, abrasive flap wheel and Brasso (!). Hardly seem to shift anything. It's as if the tiles have been hardened in some way. The marks by the way are barely discernible with a fingernail so must be a small fraction of a mm deep.
Any ideas out there - someone did mention carborundum paper ?
Cheers
Stephen
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