[meteorite-list] How to Polish Stoney Meteorites?

From: John.L.Cabassi <John_at_meteoritecentral.com>
Date: Thu, 7 Aug 2008 20:08:11 -0700
Message-ID: <006901c8f904$1e517760$4564fea9_at_TITAN>

G'Day All
I would just like to introduce myself, new to the list, but have been
watching it for a long, long time. My name is John Cabassi, you might have
seen me around on forums, I go under "Johnno", I'm Australian, but residing
in the States presently, but enough about me and more about Tom. Great post
on polishing. I'd like to see that in a more detailed explanation, maybe on
your site.

Cheers
Johnno


----- Original Message -----
From: "Pete Pete" <rsvp321 at hotmail.com>
To: <starsandscopes at aol.com>
Cc: <meteorite-list at meteoritecentral.com>
Sent: Wednesday, August 06, 2008 10:44 AM
Subject: Re: [meteorite-list] How to Polish Stoney Meteorites?


>
> 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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>
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Received on Thu 07 Aug 2008 11:08:11 PM PDT