An end to antiquities forgery? The new magnetic method that exposes fake pottery

The global and local antiquities market has suffered for years from an extensive industry of forgeries, with even the world's largest museums falling into the trap. Now, a study published in the journal Proceedings of the National Academy of Sciences presents a groundbreaking method to identify whether a pottery vessel is truly ancient or a modern forgery.

The study was conducted at the Scripps Institution of Oceanography at the University of California, San Diego, led by Dr. Yoav Vaknin, who is currently joining the Hebrew University as part of his postdoctoral studies. The team discovered how to distinguish between the magnetism accumulated by pottery at the moment of creation and the slow "magnetic memory" collected from the Earth's magnetic field over thousands of years in the ground.

"I hope that the method will assist museum curators, archaeologists, and law enforcement in their efforts to eliminate the illegal trade in antiquities," says Dr. Vaknin. The authors note that a legal proceeding held several years ago in Israel regarding the sale of fake findings ended due to a lack of unequivocal evidence for the forgery itself.

Prof. Lisa Tauxe, a geologist at the Scripps Institution, stated that the technique could be of great help to museums and governments aiming to stay one step ahead of forgers. "Forgeries are a persistent problem in almost every region of the world where archaeological excavation sites are found, including in Israel, China, and Mexico," said Prof. Tauxe.

How the method works

Pottery vessels fired in kilns absorb the signature of the Earth's magnetic field as it was at the time of their creation. The magnetism of particles in pottery created today points to the current location of the Earth's magnetic North Pole. If a rock had cooled 800,000 years ago, when the Earth's magnetic field was reversed, the magnetism of the tiny crystals within it would have pointed toward the South Pole.

The research team overcame the limitation of sample orientation by distinguishing between two types of magnetism:

1. Thermal remanent magnetism: When pottery is fired, magnetic signals of all particles tend to point in the direction of the surrounding field. Upon cooling, the signal of larger particles remains "trapped," creating a strong and uniform magnetization.

2. Viscous remanent magnetism: Signals of smaller particles never truly stabilize, so their magnetism changes in accordance with fluctuations of the magnetic field over time. This "magnetic memory" accumulates as pottery lies in the ground for centuries.

Laboratory testing

While basic knowledge of these magnetic properties has existed for decades, only recent computing power allowed for the construction of micro-magnetic models to analyze them. The method is based on gradual laboratory heating. Researchers determined 112 degrees Celsius as the threshold temperature: the secondary magnetic memory of objects 1,000 years old or older is erased only above this temperature, while in modern forgeries, it disappears at a much lower temperature.

The method was tested on a variety of vessels, from known ancient artifacts to modern pottery from Jerusalem souvenir shops. It has already been successfully applied to findings confiscated by the Antiquities Theft Prevention Unit of the Israel Antiquities Authority.

Researchers now intend to apply the method to disputed findings in museums worldwide. The study, funded by the United States-Israel Binational Science Foundation (BSF) and the National Science Foundation (NSF), is expected to change the face of the war on antiquities forgery and serve as admissible scientific evidence in legal proceedings against dealers of fake antiquities.