Cleaning A Coin With A Cotton Swab Or Toothpick

Long ago, as a boy, I learned the hard way not to clean coins, when I put an Indian Head cent (that was pretty much black) into some copper cleaner. The coin came out bright and shiny, but the surface of the coin was very grainy.

But now, as an old man, I've had a little success improving coins that have environmental damage by gently rubbing the affected surfaces with a cotton swab, being careful not to scratch the coin. I've also used a toothpick to remove some "sludge," though it's easy to scratch a coin with a toothpick.