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Elemental and isotope Credit: Copyright D. Hendin |
Demonstrating that
chemistry sometimes can inform history, researchers from the National
Institute of Standards and Technology (NIST), Colorado College and Mount
Saint Mary’s University in Emmitsburg, Md., have shown that sensitive
nondestructive evaluation (NDE) techniques can be used to determine the
elemental composition of ancient coins, even coins that generally have
been considered too corroded for such methods*. Along the way, the
researchers’ analysis of coins minted in ancient Judea has raised new
questions about who ruled the area while giving insight into trading
patterns and industry in the region.
Elemental and isotope analysis of the metals
in ancient artifacts sometimes can pinpoint the places where the metal
was mined, because ores in a given region often have a unique
composition. This can be combined with historical records of when mines
in the area were operating to determine when the coin was likely struck.
The results not only help date the coin, but also offer insight into
trade and power relationships in the region.
To compare the effectiveness of various
nondestructive analytical methods with destructive methods often used to
determine the age and origin of ancient coins, the group studied coins
minted by Kings Herod Agrippa I and Agrippa II in what is modern day
Palestine and Israel, a biblically and historically significant period.
The vast numbers of a particular coin, a
prutah, found in the archaeological record has led scholars to disagree
about when they were struck and by whom. The provenance of the coin is
important because it is used to establish dates for places and events in
the early years of Christianity and the onset of the Jewish War (66-70
CE) against the Romans and the Diaspora that followed.
To better establish whether the coins were
minted by Agrippa I (41-45 CE) or Agrippa II (after 61 CE), the team
performed X-ray fluorescence and lead isotope analysis to fingerprint
the ores used in the production of the coins. These NDE methods are not
commonly used on corroded coins because the corrosion can affect the
results—in some cases making it difficult to get a result at all. The
team showed that these problems could be overcome using polarizing
optics and powerful new software for X-ray fluorescence analysis,
combined with careful calibration of the mass spectrometer using
Standard Reference Materials from NIST**.
The lead isotope analysis, performed at
NIST, showed that the coins that had been attributed to Agrippa I were
indeed from that era. More interestingly, however, the group found that
the copper from which the coins were made most likely came from mines
that scholars thought hadn’t been opened until a century later.
“All the archaeological evidence has thus
far suggested that the Romans had moved into Arabia in the 2nd century
CE,” says Nathan Bower of Colorado College. “What this analysis shows is
that the Romans may have reached the region earlier or found that these
mines had already been opened. Either way, our findings suggest that
the Romans had a much closer relationship with this particular region
than scholars had previously thought.”
To follow up on their research, the group is
planning to perform more tests to determine if the mines in question
may have been operating even earlier than their recent findings suggest.
* M. Epstein, D. Hendin, L. Yu, and N.
Bower. Chemical attribution of corroded coins using X-ray fluorescence
and lead isotope ratios: A case study from first century Judaea. Applied
Spectroscopy, Vol. 64, Issue 4, pp. 384-390 (2010).
** NIST’s Common Lead
Standard Reference Material, SRM 981, and Neodymium
Standard Solution, SRM 3135a were used in the study.
Media Contact: Mark Esser, mark.esser@nist.gov, (301)
975-8735
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