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RE: Etching irons
Dan-
There are two things at work, one you hit on the head.
First, you hit the orientation aspect.
Second, there are some Gibeons that don't etch well.
This can be caused by the fact it has been heated - either the entire mass
at once, or just surface effects from cutting and polishing. Polishing with
too fine a grit can generate a lot of localized heat, and mute or destroy
the pattern.
Rushed cutting will also generate substantial heat.
Which brings me to this question. An excerpt posted recently from a
curator's book on desiccating meteorites @ 200 degrees C. in the oven. My
brother had been etching meteorites for a few years and I learned from
watching him. He had read or was told that at temps near 200 deg., heat
begins to obscure the pattern. My hot plates are set for 160, measured with
a thermocouple.
There are two levels of a successful etch in my 'book'.
One has the widman. pattern sharp. This seems to be almost always
attainable.
Two, is you get the pattern, AND you get the diffraction grating effect,
where the surface develops a chatoyance, looking light blue. This is more
difficult to attain - orientation seems to play a role.
Wal
----------
From: INTERNET:meteorite-list@meteoritecentral.com
Sent: Friday, March 06, 1998 10:06 AM
To: INTERNET:meteorite-list@meteoritecentral.com
Subject: Etching irons
I have had mixed success in etching iron meteorites, particularly Gibeon.
On several occasions, I have obtained a very sharp etch, which reflects
light in bright lines. Other times the effect is much more muted. I use
an
10-1 ethanol/nitric acid mix over about 30-40 minutes. Is this difference
due to the method, or due to the angle of the cut relative to the crystal
structure? Does anyone have a method which consistently produces the
bright, sharp etch?
Your help is appreciated
Dan Fronefield