[meteorite-list] meteorite slices

From: Starbits_at_aol.com <Starbits_at_meteoritecentral.com>
Date: Thu Apr 22 10:31:58 2004
Message-ID: <0E6F5D3A.5E6C379C.00848CE4_at_aol.com>

There seems to be some interest in this topic so I will add
my procedures to the discussion.

I cut everything in pure water (except irons which I rarely
cut). It is harder on the saw blades, but there isn't a
problem with additives on the slices. When a slice comes
off, it is dried on a paper towel and put into a small
 container of ethyl alcohol. When I have finished cutting
that meteorite all the slices are removed from the alcohol
and allowed to dry on a paper towel in the sun while the
next piece is cut. Nice to have a hot sunny climate most
of the year.

When everything is cut, it is off to the flat lap machine.
When I first started in meteorites most slices were
polished on a lapidary wheel and all the edges were rounded
over. I hated the look and started sanding everything on
a flat granite slab so the slices would be flat all the
way to the edges. The lap machine makes things a lot
easier. Pieces are lapped on a 220 grit diamond wheel on
both sides using water. Lapped pieces are plopped into
ethyl alcohol again until a batch is done. They are then
put on a cookie sheet, propped on each other so air gets
below as well as on top, and baked at 220 degrees for
30 minutes. They are never exposed to water again except
for what is in the atmosphere.

What happens next depends on the meteorite. I don't
believe that all meteorites need to be polished. They
need to be lapped flat to remove the saw marks, but
polishing is another story. Selma for instance looks
awful polished. It is a waste to even polish one side and
any polishing beyond the 220 grit flat lap starts obscuring
the visible chondrules. So after drying, Selma and others
like it, get one more short lap on a dry 220 grit lap wheel.
It probably isn't necessary, but I see it as removing any
oxidation or surface contamination remaining from the water
 and ethyl alcohol and leaving a fresh dry surface.

    Some have mentioned weight loss as a reason for not
sanding, but that is almost never a consideration in my
sanding decisions. Weighing experiments over the years
have shown that of a 15-20% cut loss only about 1-2%
comes from sanding and most of that is in the flat
lapping which I am doing anyway. So sanding or not
sanding makes very little difference in the final weight.
On most pieces the difference in final sanding is 0.1 grams
 or less.

    When I polish something new I polish up one side of
one piece working with "dry" sand paper on my granite slab
running through 220, 320, and 600 grits and sometimes
1200. I compare the piece each step of the way with
an unpolished piece to see what looks better or shows
off the structure better. It is an esthetics decision
which I readily admit may or may not match others views.
However, the purpose of the slice is to be displayed by
somebody and the better it looks the more likely it will find
a new home. So it is best to make it look good regardless
of any weight loss or time expended finishing the slice.
All things being equal the piece gets polished because it
removes the lines from the flat lap. If polishing darkens
a piece quite a bit usually I will polish one side and
leave the other alone so the more natural lighter version
can be seen as well.

   I don't ever put anything on a finished slice. If a
buyer wants it coated it is easy for them to do, but not
all buyers want things coated so I don't coat anything.

   I do all sanding by hand because I feel I have
better control than on a flat lap. A couple tips for
hand sanders (1) always end your polishing with a back
 and forth motion. Fine scratches left by the sand paper
are less visible than with an orbital motion.
(2) When sanding allende the CAIs will look dingy. Use a
clean 600 grit paper and make a single quick short stroke
to clean the CAIs leaving them bright white.

   Now that I have had the audacity to say not every
meteorite needs to be polished those who disagree can
start throwing rocks my way, just make them NWAs please.

Eric Olson
ELKK Meteorites
http://www.star-bits.com
       

    
Received on Mon 05 Jan 2004 04:28:24 PM PST