I am trying to decide what type of cases to keep my silver strikes in. I like the look of the Airtite cases with the foam ring in them but my boyfriend expressed concern. He told me that over time the foam might stick to the coin, or break down, giving off a gas that could harm the coin's finish. Can anyone help me here? Also, what are the thoughts about cleaning the brass rings on the strikes if they are tarnished because of exposure to air? Is this safe to do or does it harm the strike? I am thinking that the coins are probably better off just left alone. Help!