A new magnetic test may help museums, archaeologists and law-enforcement authorities distinguish genuine ancient pottery from modern forgeries. The method, developed by a team at the University of California San Diego’s Scripps Institution of Oceanography, uses controlled heating to examine how clay preserves different forms of magnetism.
When pottery is fired and cools, larger magnetic particles in the clay can preserve the direction of Earth’s magnetic field at that time. This signal is known as thermal remanent magnetism. Smaller particles behave differently: their magnetic alignment can continue changing after firing, creating what researchers call viscous remanent magnetism.
The later magnetic signal can be removed by reheating the object. According to the research team, the temperature required to erase it varies with the pottery’s age. Samples more than 1,000 years old retained the signal until they were heated above 112°C, while modern samples lost it at lower temperatures.
To investigate the difference, the researchers tested pottery with known or suspected histories, including objects believed to be thousands of years old, items purchased from souvenir shops around Jerusalem and known fakes. They heated samples beginning at 50°C, increasing the temperature in 10-degree steps.
The laboratory results were supplemented by micromagnetic computer models. These simulations recreated the heating of hypothetical samples over different periods and helped the researchers establish 112°C as the threshold identified in the study. The approach addresses a limitation of relying on the direction of a pottery fragment’s magnetic signal alone: the direction changes depending on how the sample is oriented when measured.
The researchers say the method could help institutions assess artifacts of disputed authenticity and could potentially be presented as evidence in forgery cases. The study notes that a recent prosecution in Israel involving allegedly fake artifacts ended without a conviction because conclusive evidence was lacking.
The team plans to apply the technique to artifacts in museums around the world whose authenticity is contested. Its usefulness will depend on further applications, but the researchers describe it as a possible tool for examining ancient clay objects without relying only on their appearance or claimed provenance.
