Dear All,
I often see comments about silver's diamagnetic nature when discussing using the magnet slide test. In my opinion, this is a mistake.
Silver is a conductive material. It is its conductivity that 'slows it down'.
When a magnetic field moves through a conductive material (like when sliding across a conductive coin) small currents of electrical current are formed in the coin. These are called 'eddy currents'. They are in a closed loop of current flow in the metal. These currents, in tern, create a magnetic field in opposition to the field that produced them (from the magnet). This results in a counter force that 'slows down the' magnet on its slide journey due to gravity.
How much current that flows in the eddy currents are due to the conductivity of the material (based on 'identical' coin geometries). Copper has a lower conductivity and so the eddy currents will be smaller and the retarding force will also be smaller. So the magnet will experience a lesser retarding force and will slide faster. The same sort of thing will happen with other metals that are diamagnetic. The diamagnetic aspect just means that the magnet will not 'stick' to non-ferromagnetic materials. However, there are non-magnetic stainless steels and so the same argument (above) will apply there.
Here is a vid that may help: