ERROR-missing clad layer "NICKEL"! Say what newb?
Working at a coin processing facility in the 80's and 90's, it was not too uncommon for me to encounter Dbl
Denom mint errors. Thing is, they were always of the 1c/10c or 5c/1c variety.
One day in 2000, while processing a mint bag of nickels, I chanced upon a Dbl Denom new to me - 5c/10c (COOL! Made my day!). But wait, there's more. A few moments later her sister shows up! Similar (rotated 180 degrees) to the first coin, but thin and not well struck at all. Turning the coin over I uncovered it's true beauty - a gleaming red surface! The "nickel" had been struck on a missing reverse clad layer dime (WOW! What are the odds of that happening?).
Although my hoard of mint errors from that era are largely long gone, these two remain together in my collection to this day.