If curious about the silver coins color.
http://blog.goldeneaglecoin.com/silver-coins-tarnish/
If curious about Casascius coin.
https://en.bitcoin.it/wiki/Casascius_physical_bitcoins
If curious about the silver coins color.
http://blog.goldeneaglecoin.com/silver-coins-tarnish/
If curious about Casascius coin.
https://en.bitcoin.it/wiki/Casascius_physical_bitcoins