Toning of a Coin
If you have any old, silver coins, chances are a few of them are what some would call tarnished. If you were dealing with silverware, you’d probably get some silver polish and shine it up to a brilliant gleam, but that’s the last thing you should do with a silver coin. Indeed, cleaning coins in general is almost always a bad idea, but especially those silver ones that look tarnished. People think a shiny coin is worth more because it’s clean, but cleaning coins will almost always reduce the value of your coin. The reason you should leave the coins as they are is because what some people call tarnish can significantly increase the value of your coin.
In the coin collecting world, it’s known as toning and some coins acquire a beautiful rainbow coloration to them and become collectors items. Others just like to see the toning because it confirms that the coins haven’t been cleaned or altered in any way.
In any case, if you have any tarnished (or toned) coins, take a close look at them and see how they look. Once you learn to appreciate toned coins, you’ll be glad you never dipped any in silver polish.
To read more about toning, here’s an article on toned coinage.