surface film doubling
- Here's a decent example of surface film doubling in a broadstruck
You can see shadowy letters above IN GOD WE TRUST as well as shadowy
design elements on the reverse.
This is apparently caused by a thin film of oil (or similar viscous
fluid) on the die face or planchet. The effect is more common on
nickels and clad coins, but does occur on cents from time to time.