All of the coins failed the magnet test, with an obvious fake being the Theresia taler. The Taler, with an expected silver content of 0.833 was an obvious fake due to its size, weight and lack of distinguishing features. I have many in my collection and have done a lot of research, however these coins are very often copied and loaded up to eBay.
I don’t rely on the magnet test entirely as, in my opinion, it is not reliable. It is of course better than carrying out an intrusive “acid test”, but really only shows that the coin is not made of Iron, Nickel or steel.
A Neodymium magnet would identify the diamagnetic properties of a silver content coin, but unfortunately similar properties are found in copper (widely used in faking of coins)
The Sigma PMV basic set in essence checks the resistivity of a sample, and would confirm that your sample falls within the expected parameters of the details you inputted (silver 0.999 as an example). The problem here is that copper has similar resistivity properties, so the coin may still be fake.
The PMV pro goes one step further and allows you to check the expected density of the sample (a copper coin would need to be physically larger to match the equivalent density of a silver coin of a certain purity).
The PMV database however is only calibrated for certain purities, which does not include 0.833 or 0.835 silver, so I still have to use other methods to eradicate fakes for my Theresia Talers ☹️
Sorry for the long winded answer