Researchers Have Figured Out How to Spot Fake Ancient Pottery Using the Earth's Magnetic Field

Researchers just discovered how to determine whether any piece of pottery is ancient or not—by reading its magnetic signatures. A team at the Scripps Institution of Oceanography at the University of California, San Diego, details their new method in a study published this week in the Proceedings of the National Academy of Sciences. Per a statement from the institute, the technique could help weed out falsified archaeological artifacts around the world.

When clay particles are fired in a kiln, their magnetic field orients toward Earth’s magnetic North Pole. That’s because clay objects contain ferromagnetic minerals, Vaknin, who specializes in archaeomagnetic dating, told Artnet’s Vittoria Benzine in 2022. That magnetic signal, frozen in large clay particles as they cool, is called thermal remanent magnetization (TRM), write the researchers.

Because the location of the pole is constantly shifting, the TRM of ancient pottery points in a slightly different direction than that of pottery made today. But then, after the clay cools, it’s exposed to “an ambient geomagnetic field in a different direction,” write the researchers. As Vaknin tells Haaretz’s Ariel David, over centuries, some of the clay’s minerals acquire a second, weaker signal: a record of different intensity and direction of the magnetic field.

This signal is called the viscous remanent magnetization (VRM). Scientists have known about VRM for more than a century, and they’ve attempted to use it to date geological events, reports Haaretz. But the signal is so weak, researchers usually treat it as “noise,” an obstacle in front of the TRM.

For their study, Vaknin and his co-authors tested 45 pottery samples: 4 excavated shards of ancient pottery, 15 excavated ancient royal Judean storage jars, 6 modern pottery vessels fired in traditional kilns, 16 clay seal impressions fired in modern kilns and 4 souvenir pottery vessels sold in Jerusalem. The researchers baked these samples, heating them up in increments of 18 degrees Fahrenheit. They aimed to measure at which point the VRM signals of each piece disappear, leaving only the TRMs.

The researchers determined that any sample older than a millennium had to be heated to at least 234 degrees Fahrenheit before its VRM was erased. New pottery samples’ VRMs, meanwhile, could be wiped at lower temperatures. The researchers hope the threshold they’ve discovered will aid future investigations into artifact forgery.