Researchers at La Jolla's Scripps Institution of Oceanography have found a way to tell whether ancient pottery is real or forged by measuring how its magnetic signal responds to heat.

The method, published Monday, Aug. 31, in the Proceedings of the National Academy of Sciences (PNAS), exploits a simple principle: clay fired in a kiln locks in Earth's magnetic field. Over centuries, weaker magnetic signals build up on top of that original imprint. The older the pottery, the harder those layered signals are to erase.

Postdoctoral scholar Yoav Vaknin led the study alongside Lisa Tauxe, a Distinguished Professor of Geophysics at Scripps, former Scripps doctoral student Brendan Cych and geoscientist Jeff Gee.

The team tested 45 clay objects already classified as ancient or modern. The ancient group included storage jars from the Kingdom of Judah and pottery sherds from controlled excavations. The modern group included souvenir pottery sold to tourists in Jerusalem and fake seal impressions made for the study, Haaretz reported.

The results were clear.

If a clay sample is more than 1,000 years old, its accumulated magnetism can only be erased above 112 degrees Celsius (233 degrees Fahrenheit). Modern pieces lose that signal at lower temperatures.

Scientists have understood this type of magnetism for decades, according to the Scripps research team. Computing power had not been strong enough to build the micromagnetic models needed to confirm the threshold.

As a first real-world application, the researchers tested three artifacts seized from the illegal antiquities market by the Israel Antiquities Authority: a juglet showing burn marks, an animal-shaped vessel likely used for cultic purposes and an oil lamp. All three passed, appearing to be authentic Iron Age objects potentially up to 3,000 years old.

The stakes are practical. A recent prosecution in Israel involving the sale of fake artifacts failed because of a lack of conclusive evidence, the study noted. Tauxe said forgeries plague archaeological regions worldwide, especially where deception is common.

"I hope that our new method will be useful for museum curators, who wish to display only authentic artifacts … for law enforcement authorities in their effort to eliminate illicit antiquities trade, which involves looting archaeological sites and forgery," Vaknin said.

The method works only on fired clay artifacts. The U.S.-Israel Binational Science Foundation and the National Science Foundation funded the research. The team said it plans to apply the technique to artifacts of disputed authenticity in museums worldwide.