[meteorite-list] How to Polish Stoney Meteorites?

[John.L.Cabassi]

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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