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Archaeologists had long believed the technology used to refine gold originated with the Lydians, people who lived in what is now Turkey. In the 1960s, archaeologists discovered a gold refinery dating to roughly 600 B.C.E. on the outskirts of what was once the Lydian capital of Sardis. Based on chemical residues from the site, people there likely combined gold ore from the nearby Pactolus River with salt, chalk, and animal urine. After heating the mixture to more than 800°C and letting it cook for several days, the process separates out impurities—including traces of silver naturally present in the ore—and leaves behind pure gold.
Seeking to better understand the origins of gold refining, a team led by Francis Albarède, an isotope geochemist at the École Normale Supérieure of Lyon (ENS Lyon), analyzed a cadre of 21 Egyptian and Persian silver artifacts. Those rings, pendants, small bowls, and ingots all came from the Louvre Museum. To harmlessly study the artifacts’ chemistry, Albarède and his team swabbed minute amounts of metal, just millionths of a gram, from each. Such a delicate touch was necessary, according to Janne Blichert-Toft, an isotope geochemist at ENS Lyon and a member of the research team. “No curator on this Earth,” she says, “is ready to let you rip pieces up.”
The researchers turned to silver because the metal is a common byproduct of gold refining, with natural gold typically containing 10% to 40% silver by mass. Lead is naturally found in silver, and the ratio of various lead isotopes in the metal confers a wealth of information, including whether the silver was retrieved as a byproduct of gold refining or rather was mined directly from silver-rich ores. “They are fingerprints,” Blichert-Toft says.
Albarède and his collaborators found that four of the artifacts they analyzed, all of which had been dated to earlier than 1600 B.C.E., were consistent with silver produced as a byproduct of gold refining. “It looks like what you’d expect from a gold ore deposit,” Albarède says. These results suggest gold refining had its start far earlier than in a sixth century Lydian workshop, the team concluded.
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