I have government issued gold and silver in plastic sealed pouches. For example 1/10 ounce gold maple or a one ounce silver maple. How long before the plastic affects coin surface? Is it better to just remove the coin and place it in an air-tite. I have seen the us mint proof sets that come in the envelopes from the sixties go bad but those have a different type of plastic. One reasoning for not removing the coin is perceived increase in value when selling,.