Save your time, it's harder to fake both silver and platinum than gold because tungsten is very close to gold in the specific gravity test.  You could create alloys of other metals to try and accomplish the same thing in silver, but silver has unique characteristics that gold doesn't have to give the fakes away.  All of this is completely meaningless though, as people use things like Xray machines to test them nowadays and the fakes aren't going to pass no matter what.

The common man can easily test silver.  There are not that many coin and round makers.  The simple act of pinging one of these coins will give off a unique sound wave you can either tell by ear, or you can hold it up to the microphone of a cellphone and your free cellphone app will tell you if the resonance matches and if it's real or not.  A fake silver alloy will not pass.