Well, not rust as such (there's no iron in the coin), but a metal oxide like rust. Same idea, and sometimes similar appearance.
This. So much this. The paper is NOT a friend. Foil on the outside will also tend to trap condensation. When it's warm and humid, the air inside...
Gravity is never any match for mania. Manias do tend to come and go, though.
Separate names with a comma.
