[meteorite-list] Chinga - Stopping rust and preserving?

From: John Gwilliam <jkg_at_meteoritecentral.com>
Date: Thu Apr 22 10:00:12 2004
Message-ID: <4.2.0.58.20020730091554.009cb6c0_at_pop3.norton.antivirus>

Hello Jeff and List,

According to Ivan Koutyrev, all the Chinga irons they have found have been
recovered in stream beds. This means that the irons have been in almost
constant contact with water for a long time. Over hundreds of years, rust
has been able to migrate into the interior where it can be a chronic
problem if not treated properly.

After the meteorite has been sliced, I sand down the flat surfaces starting
with a 100 grit or even a fresh 220 grit sanding belt (on a water cooled
lapidary sander). Successively finer grits are used until I'm down to a
worn 600 grit belt. Remember to wash the iron slice and rinse in anhydrous
alcohol in between every grit change so you don't have a stray piece of
larger grit mess up your polished surface. After the worn 600 grit
polish, I treat the specimen for 5 - 10 days in the alcohol/ sodium
hydroxide bath recommended by Steve Schoner. This will attack the rust in
the specimen and the sodium in the mix bonds with the chlorides in the rust
and becomes common salt. Believe me, this solution really works. I have
several slices of OLD Campos sitting unprotected out in my shop that were
treated over 18 months ago and none of them show a hint of rust. For those
of you interested in this process, I think you can find it on Eric
Twelker's website.

After soaking in the bath, I rinse the specimen thoroughly in FRESH
anhydrous alcohol and wipe it dry.

Next, I polish the slice with a muslin buff on a jewelers spindle. My
polishing unit has dual 6" x 1" stitched cloth buffing wheels that you can
mount on any motor with an arbor or spindle. My machine turns at 3,250
RPMs but a slower motor in the 1,720 RPM range will work as well. The key
to the final polish is the compound applied to the moving buff. I use a
product manufactured for the jewelry industry called ZAM. I believe it
contains chromium oxide as the polishing agent. It is a light green hard
stick in a cardboard wrapper and is available from jewelry supply outfits
and some lapidary shops. Several minutes of polishing will produce that
mirror like polish you are looking for.


Regards,

John Gwilliam


At 11:32 PM 7/30/02 +1000, Jeff Kuyken wrote:
>G'day List
>
>My knowledge of slicing and polishing irons is somewhat limited, so I was
>hoping someone may give me some advice on stopping rust in my Chinga slice.
>I would also like to know what is the best way of getting that fantastic
>mirror polish you see in so many Chinga slices and then an effective way of
>storing it to preserve that finish? Hope someone can help!
>
>Thanks,
>
>Jeff Kuyken
>I.M.C.A. #3085
>www.meteoritesaustralia.com
>
>
>
>
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Received on Tue 30 Jul 2002 12:37:47 PM PDT