Coin Thru Box

Any coin is borrowed and signed. A regular card box is shown all around. The coin is then rubbed against the box, and slowly, the coin melts right through. You can then shake the box and hear the coin inside! The coin can then be dumped out and examined. Only ONE coin is used, and the box is not gaffed! Everything can be examined... Use cigarette boxes, candy, etc... Extra ideas included.