Rust & Preserving Iron Meteorites
had a problem with a 111g Slice of Chinga which was rusting very
badly. After posting a message to the Meteorite Central Mailing
List, John Gwilliam replied with the following process which
works extremely well in stopping and preventing rust in iron
meteorites. If you try this process, be extremely careful when
handling the chemicals. Sodium Hydroxide (Caustic Soda) is very
corrosive and can easily burn skin or cause serious injury to
eyes. Always wear gloves and safety glasses. I have left a note
after the process description about my personal experience with
of 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.
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.
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 jewellers 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.
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 jewellery supply outfits and some
lapidary shops. Several minutes of polishing will produce the
mirror like polish."
I simply polished my slice by hand with various grade grits
which I found worked quite effectively. I have also used this
method on larger whole specimens such as Campo del Cielo and
Dronino with success. Other collectors and dealers have also
mentioned some success using this method on badly rusting
chondrites but I would suggest monitoring them carefully if you
are to attempt this. As to the mix in the
bath, I used a powered form of Sodium Hydroxide (Caustic Soda)
and mixed it into methylated spirits (96% Ethanol). I left a
slight excess of powder in the solution also. This worked fine
for my needs but you could probably alter this mix if
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