Pure gold is indeed weakly diamagnetic. However, some possible impurities (e.g. manganese) are paramagnetic, and will be attracted to the field. It's possible for the diamagnetism and paramagnetism to accidentally cancel, although that would be an unusual coincidence.
So we can't say that not seeing the diamagnetism proves that the gold is fake, but it does raise big suspicions. The paramagnetism, unlike the diamagnetism, is temperature-dependent, so there is a way to test for it still just using magnetic forces.
Do people ever do simple tests such as carefully measuring the density?
Archimedes figured this out a long time ago.
Lee- I know. But do they remember? /mw
(published on 06/05/2011)