[meteorite-list] How to Polish Stoney Meteorites?

[Pete Pete]

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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