My conception of a mint strike is one that is fresh out of the hopper, brand new from the supplier or kept in immaculate shape. I've never tried to clean a strike because I'm afraid I'll ruin it. I have several tarnished strikes and they will stay that way but I don't plan on selling them. I wouldn't use the word mint on anything I was selling if it didn't fit my description above. If I need a strike in my collection, I buy whatever is available but continue to look for one in better shape so I am continually upgrading. Everyone has their own definition of "mint" so if your selling or buying a strike, you better find out what the other party's definition is.