This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Museums around the world now have a new tool to distinguish real ancient clay artifacts from fakes. The research team at UC San Diego's Scripps Institution of Oceanography, led by postdoctoral scholar Yoav Vaknin, found a way to distinguish the magnetism that clay materials acquire over time from the magnetism they acquired the day they were made.
The researchers found a significant difference between modern and ancient artifacts in the temperature needed to erase magnetism acquired since the original firing. "I hope that our new method will be useful for museum curators who wish to display only authentic artifacts, for archaeologists and historians studying the societies that created them, and for law enforcement authorities in their effort to eliminate illicit antiquities trade, which involves looting archaeological sites and forgery," said Vaknin. The authors note in the study appearing Aug. 31 in the journal PNAS that a recent prosecution in Israel involving the sale of fake artifacts was unsuccessful because of a lack of conclusive evidence.
Co-author Lisa Tauxe, a geoscientist at Scripps, said the team's technique could be a boon to museums and governments that need to stay one step ahead of forgers. Fakes have been an enduring problem in Israel, China, Mexico—almost every region of the world where archaeological dig sites are found—"particularly in places where treachery abounds," Tauxe said. Pottery fired in kilns takes on the imprint of Earth's magnetic field at the time of creation.
The magnetic field, or magnetism, of particles in a clay pot created today points to where Earth's magnetic north pole is today. If a rock cooled 800,000 years ago, when Earth's magnetic field was reversed, the magnetism of its tiny crystals would point toward the south pole. But the direction of the magnetic signal in a given sample depends on how it is oriented at the moment.
Hold a sample in your hand one way, and its signal points north; roll it over, and it points south or in any number of other directions. Thus, the direction alone doesn't tell you how old the sample is. The research team overcame this limitation by first distinguishing two types of magnetism that exist in rocks, clay and other materials.
When pottery is fired, the magnetic signals of all the particles tend to point in the direction of the field, and as it cools, the signals of the larger particles remain trapped in this direction forever, creating what is called thermal remanent magnetism. But the signals of the smaller particles never really settle, so their magnetism fluctuates with the vagaries of the magnetic field over time, something called viscous remanent magnetism. The viscous magnetism can be easily erased by reheating the pottery—and the newer the pottery, the lower the temperature needed.
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