This is exactly what happens when a coin is placed at the bottom of a chlorinated pool or fountain and left there for several months. The side of the coin that was "up" gets darkly toned by the chlorine. The side that was "down" is better protected from the chemicals, and ends up less deeply coloured.
Don't say "infinitely" when you mean "very"; otherwise, you'll have no word left when you want to talk about something really infinite. - C. S. Lewis