I bought a jar of e-Z-est Coin Cleaner ($3.75) at my local coin shop. It is a blue liquid, & I rest each coin on a plastic fork & lower it into the jar for 5-15 seconds only. Amazing how well it works. In most cases it will clean the silver up to almost new. Kind of bounce slightly on the plastic fork to ensure your getting the whole coin clean...then rinse with soapy water & dry. If you rub the coin it probably will scratch it. Hope this helps.
Craig SS-1256