Frequently Asked Questions | Goldanalytix
Here you find answers to the most frequently asked questions on all topics related to precious metal testing. The questions and answers are neatly arranged according to key topics - so you can find what you are looking for very quickly.
Under certain circumstances, a counterfeit can produce a positive, i.e. diamagnetic, result on the magnetic balance if the foreign core is hidden too deep inside and thus the paramagnetic "false core" is not detected by the diamagnetic layer. The maximum thickness of a gold layer through which measurements can be taken is approximately 2.5 mm.
Likewise, a coating made of a strongly diamagnetic material that produces a strong positive value (e.g. bismuth) can, so to speak, compensate for the paramagnetic core lying further inside (which produces a negative value) and then falsify the value in the direction of "+". However, such forgeries would be difficult to produce and would require a relatively thick layer, e.g. bismuth, and would therefore be conspicuous in the weight or density test.