Further to what Marc mentioned, I've experienced false negatives which
were remedied by having first applied a few drops of dilute HCl on the
target surface.
On Sep 23, 2009, at 5:42 PM, Fries, Marc D (3225) wrote:
I've also had mixed results with the nickel allergy kit, but I think
I've
figured out how to get reasonably reliable results.
I think the problem is that the companies who make these things
probably
have liability lawyers telling them to err on the side of false
positives
(which won't really cause them trouble) rather than on sensitivity
(which
might put them in court defending against a false negative result).
This
means that false positives will occur.
You have to liberate nickel from the sample to detect it.
Weathering can do
this for you, which means that you might not detect nickel in a
fresh sample
face, especially for a polished iron meteorite.
So here's what I've found that seems to work:
- start with the unknown sample and a known meteorite - an NWA unk
will do
as long as you are sure it is a meteorite
- place a drop of vinegar on both samples
- wait five minutes, so that the acid will dissolve some nickel
- do the nickel test on both drops of vinegar
- wait five minutes, and don't get excited if they're both red at
first
- compare the results
In the event of a false positive, the swab will start out red and
then fade.
The known meteorite should stay red. If they both stay red and look
about
the same after five minutes, you've got a good case for nickel in the
unknown sample.
That's my take; I'm certain there is a lot of experience out there
on this
topic.
Cheers,
MDF
On 9/23/09 2:19 PM, "Meteorites USA" <e...@meteoritesusa.com> wrote:
Hey Mike,
I've used the nickel allergy test as well with mixed results.
Sometimes is works sometimes it doesn't. In fact I would say it is
not
reliable most of the time unless you have a good control specimen.
I kept getting false positives and even negative results on known
meteorites. In fact I took a Canyon Diablo iron that I had sliced and
tested it for nickel. Hmmmm imagine my surprise when it showed NO
results. I figure the test kit was old or out dated but whatever. The
point is it didn't work on a 100% genuine meteorite, why would I
trust
it with something I'm not sure of?
There are nickel tests that work, but I have not tested many of them.
Your best bet is to test your test kit. Testing against a known
authentic meteorite is a good method. Then test against your
"possible"
meteorite. Your results will be more reliable because now you have a
control specimen to compare results.
Hope this helps...
Regards,
Eric
Mike Hankey wrote:
I've done some nickel tests on some of the slag/meteor wrongs we
have found.
It tests positive for nickel.
Does this sound normal?
So I guess the only way to confirm slag (if you can't do it
visually)
is to cut it open and if there are holes / bubbles then it is
slag. Or
if the slice doesn't look like a meteorite slice it is slag.
For the record, I am personally looking for west like fusion crusted
stones and this is what I am training people to look for. At the
same
time when I get reports about weird rocks I have to follow up and
take
a look. Not all slag looks the same, there are a lot of different
types. I'm getting pretty good at identifying / ruling things out,
but
the nickel test threw me for a loop.
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