[meteorite-list] How to Polish Stoney Meteorites?

From: Pete Pete <rsvp321_at_meteoritecentral.com>
Date: Wed, 6 Aug 2008 13:44:11 -0400
Message-ID: <BAY141-W32DE8CE8018958F0AB7001F87A0_at_phx.gbl>

Hi, Tom,

I don't think that your site is a secret http://www.meteorite.com/meteorite-gallery
;) I think it's safe to say your images are unique in this quadrant of our galaxy.
I have all your pics rotating through my "Gadgets" on my laptop MS Visa.

Thank you for sharing your polishing methods! I see where I was going wrong - mainly my impatience.

> Is the felt pad spinning at about the same speed as the finer grit discs?

> Is the felt on top of material with some give, or on a solid backing?

> Which five grit discs are you using?

Unfortunately, the Meteorite Magazine article isn't available online, and there doesn't appear to be an online-viewing subscription.

Thanks again, and I'm sure your post will be referred to many times in the future.

Best,
Pete




> From: STARSANDSCOPES at aol.com
> Date: Mon, 4 Aug 2008 15:03:40 -0400
> Subject: Re: [meteorite-list] How to Polish Stoney Meteorites?
> To: rsvp321 at hotmail.com
> CC: meteorite-list at meteoritecentral.com
>
> Hi Pete,
>
> I am frequently polishing samples for incident light microscope work. I
> often examine meteorites at 1600X and the results are cool! This requires a
> high polish. If you haven't seen my micrographs they are at
> http://www.meteorite.com/meteorite-gallery/
>
> The most frequent mistake is to polish to fast. Previous rougher grits leave
> deep cracks and tend to pluck out crystal fragments. Each polish step must
> be given time to cut through the micro damage caused by the last step. It may
> look good with a loupe but get it on a scope at 400X+ and you will see. I use
> a six step process with 5 diamond grit disks and finish with a 1/4 micron
> Diamond slurry on a felt pad. This final step makes all the difference. You
> will notice it on a scope and it also gives that high polish "wet look" that
> really enhances a hand sample.
>
> When I say "to fast" I am not talking about platter speed but rather the
> time spent at the wheel. I bring music and sometimes a magazine (never a book
> I don't want damaged). Even on small 20-40mm samples I may spent a half hour
> on one of the finer grit levels. The rough grind takes only a few seconds
> but the fine grit is time consuming.
>
> I am sure you can get a beautiful hand sample finish with less time than
> what is need for scope work.
>
> The August 2006 Meteorite Magazine had an article (From the Strewn Fields)
> by Martin Horejsi. He came out to my place and we put in many hours polishing
> some of his historical meteorites. (He has an awesome collection!) He
> wrote a cool article describing the process. I don't know if Meteorite articles
> are available on line.
>
> Tom
>
> In a message dated 8/4/2008 12:22:26 P.M. Mountain Daylight Time,
> rsvp321 at hotmail.com writes:
>
>
>
> 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 Wed 06 Aug 2008 01:44:11 PM PDT