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Silver Isotopes and the Rise of Money

Periodic Reporting for period 3 - SILVER (Silver Isotopes and the Rise of Money)

Reporting period: 2020-10-01 to 2022-03-31

Although the ancient link between money and precious metals has been progressively dissolved, the rise of silver money still resonates with modern economy. ‘What is money?’, a commodity or rather a standard of value, is still a modern question. This question is probably better formulated in societies in which credit was not as common as today, central banks did not exist, and different forms of metal coexisted, notably coinage, silverware, and cult objects.
The objectives of the SILVER project relate to these questions by using lead and silver isotopes as a tracer of metal extraction, minting, and circulation. Lead is a metal always found in trace amounts in silver objects and the relative proportions of its isotopes vary over a broad range in rocks. Lead isotopes have been used for half a century by numismatists to fingerprint the ore deposits serving as the source of silver. A major ambiguity is that lead used for smelting may simply be foreign to the silver ore. Silver isotopes, which have been introduced to numismatics by our group in 2011, are not affected by this ambiguity because they belong to the metal that carries the value. Their relative abundances, however, unfortunately vary over only a very narrow range since, contrary to Pb isotopes, the cause of variation is purely thermodynamic. The purpose of the proposal is twofold. First, the development of early coinage in Greece, Ionia, and the Eastern Mediterranean will be traced. The relative weight of each production locality and the proportion of minted metal will be assessed. Second, we aim at monitoring the advance of monetization of the Mediterranean through the rise and fall of the competing empires, notably Persia, Greece, Macedon, Carthage, and Rome. Collaboration between geochemists and experts of history and numismatics will be decisive in documenting the rise of money from a new perspective.
A major hurdle has been the sampling of silver coins. The curators of all the major collections we have approached for samples decline drilling. A very successful workshop run by SILVER at the Louvre Museum in Paris in early February 2020 was attended by curators, geochemists, historians, and numismatists and produced new guidelines for scientific sampling.
The coupling between silver and lead isotopes in ores and coinage illuminate the smelting process, the relative importance of the different mining districts, in particular Thrace vs Attica. A survey of lead isotopes in denarii minted by the Roman Republic demonstrated a major gap between the coins struck during the 2nd Punic War and those produced during the second half of the 2nd century BCE and after, which demonstrates a major shift in silver supply. The next step was the study of correlated variations of silver and lead isotopes in Roman denarii, which showed that the coins of the 2nd Punic War were struck from recycled silver in bulk and pre-existing coinage corresponding to the war indemnities paid by Carthage at the end of the 1st Punic War. In contrast, the Roman silver coinage of the late 2nd century was struck from silver produced in Spain using smelting processes developed by Phoenician colonists since the 8th century BCE.
The Roman denarii contrast with the coinage of classic Greece and its colonies in their visible decoupling of silver and lead ores. The Greeks and most of their colonies seem to have been using local lead to extract silver, whereas Phoenicians, and after them Carthaginians and Romans, had to bring foreign lead to the sites of silver extraction. This suggests that the silver ores used by the Greeks were essentially lead carbonates and sulfides, whereas in the Iberian Peninsula silver-rich sulfates had to be combined with lead extracted from galena.
Combining silver and lead isotopes indicates that contrary to more normal times when silver is delivered by the mines, the Roman recalled and remelted silver from the civil society at the climax of the second Punic War.
A new statistical technique (the convex hull) is now allowing us to delineate the regions of silver provenance in the 3-dimensional space of lead isotopes. Lead isotopes in Levant hoards of hacksilber buried at the end of the Bronze Age, the time of the Greek invasions, demonstrate that silver essentially came from Attica, Thrace and Macedonia with possible contributions from Southern Gaul. Iberian silver was surprisingly subordinate. The Levant silver 'mix' was clearly aggregated by circum-Mediterranean trade.
How much Persian silver (sigloi and alexanders) was derived from the huge tributes paid by the Aegean world to the Achaemenid Kings, and how much was derived from mines of Persia and other regions? Our results now demonstrated that the 'Persian mix' was dominated by Aegean silver.
we also developed tools to identify the silver mines used by Greeks and Romans. The range of silver isotopic abundances in silver coinage, whether from the ancient circum-Mediterranean world, medieval Europe or from colonial Americas is incredibly narrow (<0.02 percent) while the range in ores is over an order magnitude broader. We found in both Spain and Greece that the few ores containing argentiferous lead sulfide at a high concentration level were also those with silver isotope abundances matching those measured in coins. These ores also have very large concentrations of antimony, which is a sensitive tracer of atmospheric pollution by ancient metallurgy. The sulfide mines with silver isotopically different from the coinage reference cannot have been significant sources of bullion.
Given the current emphasis on the usefulness of lead model ages for provenance studies, we set out to understand them in Iberia and in Greece. We have now demonstrated that these ages are not emplacement ages but correspond to the primary concentration of lead during oceanic anoxic events.
Chromatographic methods required to separate and purify silver, lead, and platinum group elements in coins, artefacts, and ores have been developed or improved.
We will now try to shed some light on the dynamics of monetary silver mass in the Eastern Mediterranean in the 6th-4th centuries BCE. Our partly unpublished data consists of about 600 data for Pb isotopes, 150 on Ag isotopes for coins, 150 Pb data and 150 Ag data for ores). The data show that Athens acted as a monetary hub for the Eastern Mediterranean, whereas some other places (e.g. Thasos) were simply bullion sources, and other could just rely on tolls and other silver fluxes (Corinth). A innovative study of platinum group elements in Greek coinage is showing that gold parting from silver was limited to Athens and some of its colonies but was not a ubiquitous practice. Tasks still to be accomplished are the bearing of our data on monetary fluxes around the Mediterranean. A successful field trip to the Balkans, largely terra incognita for isotopes, brought back about 100 samples of lead ores, which may help understand the rise of the financial wealth of the Argead dynasty, who culminated with Alexander the Great.
Athenian silver Tetradrachm "Wappenmünzen" struck in 515 BCE at the time of tyrant Hippias