Obviously
thin gold plated not long after issue.
Thick gold plating not really affected.
Over a period of many years, the gold and the nickel atoms migrate in both directions across the gold Cu/Ni plating interface. Even if the coin has been protected in a capsule, the coin will
still pale in the long term.
I found this out for myself when I had a .925 sterling silver coin gold plated. Looked really nice to begin with, but disappointing in the long term.
Thus, over many years, the appearance
will pale, due to a combination of
wear, and atomic cross migration at the plating interface, as mentioned above.
Definitely a curiousity keeper. With coin pictured, plating doesn't seem to be thinned on the high points, due to
wear.
I have quite a few plated World coins in my collection, all taken from dealers' junk boxes at below normal price for condition, because they are really
PMD.
Still, I like 'em all, anyway
! 