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 by the MagneticScreenScale 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.