The reverse looks like the Copper/nickel layer was eaten away leaving the copper core. The teller told me the customer who brought it in said it was a result of hurricane Ike so I amagine it was soaked in all kinds of toxic stuff.......ewwww.
To me it looks like it received some type of failed copper wash. I would expect that if the cladding were "eaten away" that there would be detectable ridges since the cladding soes have a measurable thickness. Regardless, it looks pretty cool and one which I'd keep.
