Magnetic Clues Could Help Expose Fake Ancient Pottery

A pottery fragment may carry a hidden record of when it was fired—not in an inscription or decoration, but in the changing magnetic field of Earth. Researchers at the Scripps Institution of Oceanography at the University of California, San Diego, say they have developed a method that could help museums, archaeologists and law enforcement assess whether clay artifacts are genuinely ancient. Their findings were published in the Proceedings of the National Academy of Sciences, according to Smithsonian Magazine. When clay is heated, magnetic minerals inside it align with Earth’s magnetic field. As the object cools, that alignment becomes a lasting signal known as thermal remanent magnetization, or TRM. Because the planet’s magnetic field changes direction and intensity over time, pottery fired in different eras can retain somewhat different magnetic signatures. The researchers focused on another signal in the clay: viscous remanent magnetization, or VRM. After pottery cools, some minerals gradually record the surrounding magnetic field, creating a weaker, later signal. The team’s approach measures how much heat is needed to erase that newer signal and reveal the original one. For the study, the researchers tested 45 samples. These included excavated ancient pottery shards, ancient Judean storage jars, vessels made in modern traditional kilns, modern clay seal impressions and souvenir pottery sold in Jerusalem. The samples were heated in increments of 18 degrees Fahrenheit. According to the reported findings, samples more than 1,000 years old needed to reach at least 234 degrees Fahrenheit before their VRM signals disappeared. Signals in newer pottery could be erased at lower temperatures. The researchers say the distinction does not require extremely fine resolution; the goal is primarily to determine whether an object is ancient or modern. The team also applied the technique to three artifacts of uncertain authenticity that had been confiscated by the Israel Antiquities Authority. The results indicated that all three had been fired in ancient times, although the method is also intended to help identify genuine objects that may have been looted or illegally traded. The researchers acknowledge that authentication remains difficult because forgers can study published scientific methods. Their work is presented as a potential tool for investigating questionable artifacts, not as a complete solution to the international trade in archaeological objects.