Earth's magnetic field can help archaeologists sniff out forged antiquities

Researchers at the University of California San Diego have developed a new method using Earth's magnetic field to help archaeologists distinguish between authentic ancient artifacts and modern forgeries. The technique focuses on fired clay objects, which retain a magnetic signature from their exposure to the planet's geomagnetic field over time.

Led by geophysicists Dr. Yoav Vaknin and Prof. Lisa Tauxe, the team published their findings in the Proceedings of the National Academy of Sciences (PNAS) on Monday. Their approach relies on analyzing the Viscous Remnant Magnetization (VRM), a weak magnetic signal that accumulates in clay over centuries. Unlike the stronger Thermal Remanent Magnetization (TRM) acquired during initial firing, VRM continues to develop as minerals in the clay react with the Earth's magnetic field. Modern clays lose this signal at lower temperatures, while ancient ones retain it until heated above 112 degrees Celsius (233 degrees Fahrenheit), indicating an age of at least 1,000 years.

Archaeologists often face challenges when artifacts lack documented provenance, such as those from illegal antiquities markets or private collections. Without excavation context, determining authenticity becomes difficult, even with existing scientific tests that forgers can sometimes circumvent. The new VRM-based method provides a supplementary tool for authentication, particularly for artifacts predating the medieval period.

In their study, Vaknin and colleagues tested 45 clay items, including ancient storage jars from the Kingdom of Judah, modern vessels, and fake artifacts. They also examined three disputed artifacts recovered by Israel's Antiquities Authority, which appeared to be Iron Age pieces. All three passed the VRM test, suggesting authenticity.

While the method cannot pinpoint an artifact's exact origin or date, it effectively identifies forgeries, giving researchers an edge in combating fraud in the antiquities trade. The constant evolution of forgery techniques poses an ongoing challenge, as those producing fakes can study scientific methods to evade detection.

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