Can silver purity be tested via magnetic field or resistivity?

Question

Let's say I have an alleged pure silver coin sealed in plastic. I can know the exact weight and dimensions of the coin.

Is there some way to determine the purity of the coin? Because silver is the best conductor, could that property be leveraged by magnetic field induction or some such method to determine the purity of the silver? Especially, determine without doubt that an item was at least 99.9 pure?

If not via magnetic field, what about a resistivity test? If one could put an ohmmeter across the coin (which would require contacts through the plastic seal)?

Answer 1

Yes, you could test silver by measuring magnetic properties or electrical properties.

These tests would be very difficult as you would need to know the dimensions and set up very accurately and do very precise measurements.

In your theoretical example you say you know the weight and dimensions exactly. It that case you could also calculate density as a test (a common test in the past).

However all these measurements can be "faked". You could make a Silver plated nickel alloy with similar magnetic properties (thou with some difficulty), or a gold compound with similar resistivity or a lead alloy with similar density.

If you combined measurements and they all confined silver you could be pretty confident it was pure silver.

The true test is to take a small sample and do a mass spec. This is a test that specifically measures atomic properties giving the percentages of elements in a sample. These tests can detect very small amounts of impurity (0.000000001g of lead per 1g could easily be detected in some detectors) .