[meteorite-list] How to Polish Stoney Meteorites?

From: Pete Pete <rsvp321_at_meteoritecentral.com>
Date: Mon, 4 Aug 2008 14:21:55 -0400
Message-ID: <BAY141-W236D93FD7E06A3C5C8A8A7F8780_at_phx.gbl>

Greetings, fellow Meteoriteheads,

Here is a topic rarely discussed on the List, but one that I think many of us could benefit from.
The only references I find on the web are for polishing irons.

I have been trying to mechanically polish some of my stones and I just can't get the same glassy finish which I see on some of my purchased samples, or even close to what I have done by hand with 1500 grit wet paper as the finishing stage.

I am using four diamond polishing discs: 100, 600, 1600, and 3000 grit, using distilled water for lubrication.

After I cut the stones open they are quite smooth, and I only use the 100 to get rid of the small nub when it breaks off at the end, or the most visibly non-level surfaces, if necessary.

I hold the stones on the remaining three discs for about five minutes each - when it feels like there is no more abrasion taking place.
The finished product is a glassy-smooth surface to the touch, but without the glassy-smooth, shiny appearance.
Under the microscope I can see very fine scratches from the discs, which I don't see when I polish by hand.


A while ago, someone (I think our Dean Bessey) once made mention of a rule of thumb for mechanical polishing as, "grind fast, polish slow". (I hope I'm not recalling this backwards!)


My questions are; 1. How slow? I don't expect an RPM answer, but would it be the same relative speed that the hand would be moving, if the (final) disc was stationary?

2. Am I just being impatient, and it takes a lot more than five minutes at each stage, even though there doesn't appear to be polishing taking place?
How long should each stage realistically take?

3. Is there another finishing step after the diamond discs?

4. Is there too much of a leap between the grits I have?

5. Is there such a thing as too much liquid lubrication which would reduce the desired grinding effect from the discs?

For the sake of argument, let's use NWA 869 as the meteorite to polish.

Kind regards,
Pete






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Received on Mon 04 Aug 2008 02:21:55 PM PDT