Can sunlight affect a mint state or proof coins luster?

Answer 1

I could be wrong, but I don't think so. Mint luster is imparted on a coin by the effects of the minting process. It is a physical aspect of the coin. Unless sunlight alone can change the physical aspects of the coin I don't see how the mint luster could be affected.

Other elements in proximity or in contact with a coin may be affected by exposure to the sun and thus cause a change to the coin (think plastic holders) but I don't think just sunlight can do the job.

Of course I don't expect to leave such high quality coins exposed to any long term sunlight either.

Interesting question.

Answer 2

Sunlight alone won't damage the mint luster, but can increase the humidity that causes the metal to react quicker with the various sulfur-based compounds in its environment, resulting in faster toning on the coin surfaces.

Answer 3

It sure can, Putting coins in a window is a way some people tone them, after they cleaned them wrong. It effects copper coins more than the others, but over time will effect them too. Another thing, leaving coins in paper wrappers for a good many years, will also tone them. People have had rude awakenings after leaving coins in original paper wrappers for 10-20 years. The acid from the paper can actually eat the metal if stored for a lot of years.

Answer 4

Yes, any type of metal surface is affected by sunlight. UV rays will cause coins to lose their luster. UV Rays will affect the shine on a car, metal building, your outdoor furniture etc etc. When you buy an official set of coins, a good seller will have them encased in a UV resistant wrapper.