There are density calculations that you can do with water displacement. The chemical test will show positive for plating as well as pure silver.
Here are some ways to validate:
Certificate of authenticity from a reputable mint
Magnet test - if it's magnetic, it's not pure silver
Chemical test - Only for certain valid if you file deep into the coin and test the shavings. For thicker bars, you will need to drill randomly.
Specific gravity test with water displacement