|
|
| Author |
Message |
| 3 new of 27 responses total. |
bdh3
|
|
response 25 of 27:
| 
May 29 04:29 UTC 2002 |
I actually purchased a modern replica off an ebayer who was
taken by a seller. It had an NMR spectrograph showing no
silver content whatsoever - mostly copper-nickel. Yes,
specially with coins the non-destructive test is the one
to use, thus weight/dimension and microscopy up to now.
Clever fakes require more clever detection and NMR looks
like a good bet for composition- but unfortunately is well
beyond most collectors (not everyone has friend with access).
|
lynne
|
|
response 26 of 27:
|
May 29 16:02 UTC 2002 |
I'm not very well up on solid-state NMR, particularly of metals. But #24
has a valid point. Seems like too much metal to be effectively studied by
magnetic resonance.
I don't think it'd be great at isotopic composition determination,
necessarily. For one thing, each isotope you study has to have an NMR-
active nucleus and I believe each separate NMR active isotope needs its
own frequency. You can't accurately determine the ratios of different
isotopes (or metals, for that matter) either, so far as I'm aware. Ya gotta
figure that whatever isotopes are present in one coin are probably also
present in a fake; it's only the ratios that change.
That said, I find I know astonishingly little about determining metal
compositions in a metal. I'd pretty much have to take a sample and dissolve
it in order to apply most of the techniques I'm familiar with.
|
bdh3
|
|
response 27 of 27:
|
May 30 03:55 UTC 2002 |
Someting you don't want to do with coins is anything that effects
the coin, especially appearance. It is generally enough to determine
that there is no silver in what should be a .900 silver coin to
determine it is a forgery. A .900 silver coin might still be
forgery. Isotopic analysis would not determine a forgery made
from contemporaneous material from the genuine article -indeed that
is somewhat of a small problem, some forgers make more valuable coins
out of genuine but less valuable. Thermoluminescence I believe is
of value in articles such as pottery - and the potters have taken to
grinding up old pottery shards to either glaze the item in places
where samples are likely to be taken, or incorporating into the
base clay. I'm not sure how well it would work against reworked
genuine coin. The presence of radioisotopes from nuclear testing
and fallout in the coin might seem promising, but the necessary
cleaning perhaps destroys much of the value and the cost of testing
probably renders it useless.
Right now, the Mark I eyeball (and tongue) -assisted perhaps by
optical enhancement (even a simple jewelers 5x loupe)-along with
a good scale and calipre or even ruler (or dimensional chart)
are unfortunately probably the best tools. That and the knowlege
of what the coin should look like, and sometimes even feel like
or sound like. That and common sense.
|