When Thomas Hoving stood before a 2,000-year-old marble kouros — statue of a nude Greek male — one word flashed in his mind: Fresh.The J Paul Getty Museum in California had tested the kouros against fakery — the kouros had passed the test. The thin layer of calcite stamped it right — after all, it takes thousands of years for dolomite marble to turn into calcite.Yet Hoving, a former Director of the Metropolitan Museum of Art in New York, thought ‘fresh’.Opening his book, Blink, Malcom Gladwell describes how it took teams of experts to determine that the kouros was fake, while Hoving and a few others spotted it right away, intuitively.Suppose you are an ancient-pottery forger. You have done a magnificent job. The clay is right. The shape is perfect. You have even given it a suitably battered appearance.There is just one problem.The earth remembers. When clay is fired in a kiln and cools, tiny magnetic minerals inside it line themselves up with the earth’s magnetic field, rather like microscopic compass needles. The resulting magnetic signature gets locked into the pottery. This is called thermal remanent magnetisation, or TRM.Now, here is the catch for our unfortunate forger: Earth’s magnetic field does not stay put. Magnetic North wanders over time. So, a pot fired 2,000 years ago carries a subtly different magnetic signature from one made yesterday.But there is more. Over centuries, ancient pottery slowly picks up a second, much weaker magnetic signal from the earth’s changing magnetic field. Scientists call this viscous remanent magnetisation, or VRM. For more than a century, researchers have largely regarded it as a nuisance — noise interfering with the stronger original signal.The idea is deliciously simple: An ancient object has had centuries to acquire this secondary magnetic memory; a modern forgery has not. While this technique cannot tell you if the pot was made in 321 BC or 431 BC, it can assure you that it was not made last month.Now, how did the kouros forger get the calcite layer? Well, turns out that you can ‘age’ dolomite marble using potato mold.But that was in the early 1980s. Today, dear forger, things are different.Published on September 7, 2026