Rare mint error double struck cent find

I spent about 2 hours yesterday at a new site. Downtown some houses were torn down and the lot was standing vacant for several months now. The ground was so full of pennies that notched out everything below a dime. I know  you miss the gold jewelry and lots of interesting things but I was tired of digging them and had limited time. When I got back to the truck I looked through the coins. 5 dimes 14 pennies all clad. and a hotel token good for a trip to the beach. I looked closely at one of the pennies that puzzled me when I dug it out. It was a 1981 clad and part of the copper was still shiny. See photos. With a little internet research I found this was a rare mint error coin. What's known as an double strike overlay. This occurs when a previously minted coin enters the die at the same time a coin is stamped and the two coins are stamped together. This welds the coins together making some interesting looking coins. This one is particularly rare in that the obverse of the coin has the image of the reverse and the reverse side of the coin has the image of the obverse. This happened when three coins were in the die or when 2 coins were in the die on the first strike and a the overlay-ed coin got stuck in the die and a third coin was struck on top of it.  However it happened it is bizarre. What is even more bizarre is that the copper from the overlay was still shiny. This coin was down 3 " in among oak tree roots the size of my thumb meaning it had been in the ground a while. All the other cents from this site were tarnished as is common for copper coins at that depth. Apparently the overlay protected the metal from oxidation. Just how that works I'm not sure. The first thing that comes to mind is that the copper/zinc/copper/zinc overlay formed an electrical battery that protected the surface layer. Sort of like anodizing. Gambol.

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http://www.thunting.com/smf/index.php/topic,37083.msg228132.html#msg228132

Brilliant find you have there! Congratulations.

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http://www.thunting.com/smf/index.php/topic,37083.msg228149.html#msg228149

Wow that is amazing, well done on that find... Now you need to find some way to preserve this find 

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http://www.thunting.com/smf/index.php/topic,37083.msg228233.html#msg228233

Keep us informed, will be interesting to see how you do  Don't get robbed though 

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http://www.thunting.com/smf/index.php/topic,37083.msg228352.html#msg228352