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Concentrated Acids Are Dangerous!
If you have NOT worked with these chemicals before,
find someone who has experience using them
to guide you through the following process.
At some point in time all of us buy an iron meteorite which
for one reason or another begins to show rust and needs
attention.
All meteorites needs to be treated with respect and care
and most of us are keenly aware of this, but irons can
disintegrate remarkably fast.
Sometime we find slices we want and have no idea of how
they have been prepared. Other times it is obvious that they have
been coated and handled carefully by the preparer. I got an
endpiece of Toluca at Tucson and before I could even really get
home I looked at it again, it was really rusted. 
It may not
been neutralized properly after etching and had not been coated
with anything. Well, I had only the time at that point to prevent
further damage, and will now undertake with you the process of
re-facing, polishing and etching it.
Paul, got a very nice slice of Canyon Diablo which has graphite
nodules. It began to show rust spots around the nodule soon after
Tucson also. 
We will show the process of
restoring it also.
The Toluca end piece is not an expensive piece and it had a
lot of unremoved rust on the surface when I got it. I will not
remove it but will stabilize it with a coat of Krylon acrylic
spray to keep it from flaking off anymore. On the cut surface I
have re-sanded it down smooth, finishing with 600 grit wet dry
sandpaper. It is nearly polished at 600 grit so on this piece I
won't actually polish it.
I would have to wash it to
remove the polishing compound and that would create more problems
with the loose back side than it is worth. Especially since this
Toluca had a rather bold figure when etched.
Paul has carefully sanded with 220, 400, and 600 grit paper
and is ready to re-etch the Canyon Diablo slice. 
I prepare the etchant in small batches as I need it and do
not leave it around. You may if you wish prepare a large batch.
The exact etchant formulas are available in books on meteorites,
but almost any solution of anhydrous alcohol with around 5%
nitric acid will work. I vary the formula slightly sometimes
depending how the individual piece is etching, this means a drop
or two more or less acid. It is never a strong acid solution.
Never! Anyone attempting this should obtain a basic chemistry
textbook and read the information on the safe handling of acids
and the proper methods to mix acids and water and acid and
alcohol.
I use both alcohol and aqueous etchants depending on which
produces the brightest figure. It may be necessary on occasion to
cover nodules and areas of troilite to prevent the formation of
stains which may form from reactions of these substances with the
etchant. This can be done with a fine point artist's brush and a
clear coating material which is impervious to the etchant. Some
of the plastic sprays do not resist the pure alcohol and
dissolve. Test before using with etchant to see how it works if
you intend to cover any of the areas of the meteorite. I have
never had much of a problem with this. When stains appear I
continue the etching until it is done then after a first rinsing
I go carefully back to the stained spot with etchant and wipe the
stain off and immediately neutralize and rinse again.
This is somewhat an artistic operation. The figure I like
may not be what someone else etching the same piece would leave
it with. I have pieces which I know would etch different if I
redid the work. But I leave them alone because that has become
the character of that particular piece for me. So the bottom line
is when the figure appears as you apply the etchant let the acid
work till your happy then move it quickly to the neutralizing
bath.
Many methods have been devised to apply the etching
solution. On small slices or surfaces I use a cotton swab which I
move quickly to cover the surface and them very randomly wipe
across the surface till the uniform figure is attained. On a
larger piece as with Paul's Canyon Diablo I poured a small amount
of etchant enough to well cover the surface and then used a
swatch of old cotton cloth to move the etchant over the surface.
I had to rise and reapply several times to bring up the figure
properly.
For neutralizing the meteorite at the end of etching I use
a strong solution of baking soda dissolved in water. I also keep
a large bottle of this near at hand while etching in case I spill
the etchant I can neutralize it and prevent damage to the work
area, tools, or personal injury. A face shield, rubber gloves,
and all regular acid handling precautions are to be used during
this process. Nitric acid in concentrated form is dangerous and
will fume, and froth, and create heat if mixed improperly. It is
essential that the alcohol you use be water free. Anhydrous
Isopropanol, Anhydrous Ethanol will both work well.
You will need these water-free alcohols later to soak the
meteorites in to remove the water, remaining acid, chlorine, and
other potential problem chemicals from the metal. I often soak
the meteorites for some time after etching if they have a rough
surface or have inclusions or nodules. It is near the crevices
and cracks that the rust usually begins so leaching out any
residual chemicals with alcohol in these areas for a period of
hours or longer can help a lot.
After you are confident that any residual acid or water is
out of the meteorite it is time to dry the specimen. I like to
use a blow dryer so that the specimen can be gotten a little warm
to drive the liquid from the crack and off the rough surface.
Some people like to place them in a warm oven. The most important
part though is to make sure the surface you have etched dries
fast and evenly without spots. Do not touch the surface with your
hands. Pick it up by the edges, move it on a piece of chipboard
or plastic, whatever works for you but don't touch the surface
you etched.
Once the piece is dry you should coat the surface with
something clear to protect it from moisture. I use Krylon almost
exclusively now. But I have been told by experts that it does not
work well on all irons. Shellac was the choice of Nininger in the
past. He did not have plastic in spray can but he was a careful
preparer and shellac served him well.
As I said earlier I sprayed the loose rust on the back of
the Toluca to stabilize it. I then sprayed the etched surface and
let it thoroughly dry. I do the spraying on a piece of glass or
plastic to prevent the possibility that the specimen will stick
and tear away fibers of paper when it is dry and I lift it off.
These would have to be removed and might show as scratches in the
clear coating. Use several light coats on the back side so that
there will be no runs which might get down to the already
complete front face. 
If this sounds overly careful, let me assure you that the
results of a beautiful slice with a flawless surface more then
compensate for the trouble and care. You will have a museum
quality or better meteorite every time after a few tries. 
Often the specimens are etched only to show the basic crystal
structure. When you do it yourself you can continue the process
to bring up Neumann lines or to define the twinning of the
crystals. Many details can be enhanced by careful observation
during the etching process.
Before and after images of the Toluca 
and Canyon Diablo. 
This area of The Meteorite Exchange is always open for contributions from others with varying experiences in care and preparation of meteorites. I am always happy to hear from others, since I am not an expert at much, I can always learn and appreciate the opportunity to be taught.