How can pre-Columbian gold be authenticated?

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Clarification of Question by wjcl3-ga on 04 Apr 2005 10:45 PDT

I can add this: The artifacts in question do not appear to be formed
of a modern alloy; they are 90% Au/4% Ag + 6% Cu alloys, without any
other apparent trace elements as measured by superficial EDXRF. It is
presupposed that they were cast from pre-Columbian 'placer' gold which
had an Ag content of about 4% naturally. Modern 'placer' gold
generally has industrial contaminants. No modern casting materials
have been found microscopically, nor are any modern casting flaws
evident. Apparent ancient casting flaws are abundant microscopically.
Although the surfaces have been cleaned, large areas were never
polished and appear intact. Since these would have been
low-temperature, gravity castings, is there anything about the
crystalization patterns that can be illuminating? Or anything else,
for that matter.

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Clarification of Question by wjcl3-ga on 19 Apr 2005 09:44 PDT

The gold artifacts are Costa Rican, who only signed onto the UNESCO
treaty and implemented national laws recently. These particular
artifacts have been in this country legally for some time now. Sadly,
90% of all artifacts examined scientifically by a commercial
laboratory over a period of 30 years turn out to be fake. They are
usually pedestrianly so and easily detected by a trained eye. That
same lab reports that the artifacts in question are authentic. My
problem seems to be that the artifacts in question are just 'too good
to be true' in the eyes of the iconographers or style watchers, who
dominate the field.

I would think that a low-temperature, gravity casting of an alloy of
Au/Cu/Ag could be scientifically distinquished as having been cast 20
years ago or 600-800 years ago.

And yes, if they are authentic, they are extremely vauable.

I believe it is possible in some cases to identify where metals came
from by analysing their isotopes.  Whether this is possible for gold
from the Andes or elsewhere in South America, I do not know.  The
following website was the first one I found that mentions the subject:
 http://www.ucalgary.ca/~iyer/igcp450/unesco/news1.htm

If it is possible for Andean gold, then at least one could identify
fake pre-Columbian articles that were made from gold from another
source, which would probably be the case.

Thanks for the clarification. I cannot help you, but maybe and
additional comment - visible to scrollers-by on questions -  will
suggest to someone to look at your question again.
I hope so, and good luck.

Do you want to know the date of the gold, or the date of the casting?
Seems like it would make a difference, as a forgery could be made from
"old" gold. myoarin is right in that isotope/ composition ratios may
be able to give you a handle on point of origin. However I dont think
they would be too usefull in determining age. Again, hoping the
additional comment draws eyes.

HI wjc13,

Is there ... maybe better: what is the record on conterfeit
pre-Columbian gold artifacts?  With my very amateur search techniques,
I didn't find anyting on the subject or about testing or
authentication.

I assume that you have no doubts from comparison with museum pieces
that the items appear to be entirely in the correct style.  Someone
taking the effort to make a fake that seemed so correct from the gold
content and (apparent) use of pre-Colombian casting techniques would
certainly have done his homework for the style too.  But he might have
combined design elements of different pieces, something that could
MAYBE be identified by thorough research, but if it could not be, that
would be no proof of anything.
The Jan Mitchell Collection at the NY Metropolitan Museum seems to be
the name that keeps coming up.
Are such artifacts so expensive (in the illegal market, since they
cannot be taken from Peru(or ?) now, to make it worth the effort of
using (finding and buying uncontaminated) placer gold and doing all
the work?

I don't know.
Good luck.