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Everything you need to know about buying, selling, and authenticating gold bullion.
The full physics of the Coin Cradle and the ping test, with derivations and data. Summarised in The Physics of the Coin Cradle and What the Ping Test Can and Cannot Do.
A first-principles model of the Coin Cradle: the magnet, the eddy currents in the coin, the energy lost on each pass, and the ratchet dial. With nothing fitted, it predicts the readings to 12%. Technical report included.
A correction: the old single-frequency ping check rested on theory values and a ±3% gate that do not hold up. What a phone can measure instead, and how ping, pendulum, weight and size work together (modelled). Technical report included.
Why combining acoustic resonance with electromagnetic damping makes simple fakes hard to build, the assumptions behind that argument, and the layered fakes that can still get through.
A comprehensive guide covering every method used to detect counterfeit gold bullion, from simple weight tests to advanced eddy current analysis. Learn the tell-tale signs that separate real gold from sophisticated fakes.
Not all gold coins are created equal. Discover the practical differences between 22-carat and 24-carat gold, and how purity affects weight, density, and authentication readings.
Tungsten matches gold in density almost exactly, making it the counterfeiter’s material of choice. Find out why traditional tests fail and what technology can catch it.
Eddy currents are induced loops of electrical current created by a changing magnetic field. Learn how this phenomenon is harnessed to authenticate gold non-destructively.
Thinking about buying your first gold coin? This guide covers everything from choosing the right coin to storing it safely and verifying its authenticity before purchase.