I know Jim, I realized and understood your thoughts all along. But that doesn't change anything for me for I still have to believe what I see with my own eyes. For years I have recommended a very simple test for those who just can't believe that gold tones. Buy a freshly minted gold coin, leave it out and exposed to the air. A year or two later take that coin and go to a local shop. Put it on the counter and look at it side by side with a new, freshly minted gold coin. You will see a difference in color with your own eyes. From that point on if you still don't believe that gold tones, well, I don't know what to tell ya.
Keep in mind that many gold coins are alloyed with copper and other metals. I realize some Mint products are 0.9999, but those trace metals are going to tone and they will probably impart a change in the appearance given enough exposure to air.
Given that argument Thad, not that I agree with it at all, the bottom line is still that gold tones. .999 or .9999 is as pure as gold gets. So based on your argument that even .9999 gold has impurities and it is the impurities that are toning, then it cannot be said that gold does not tone. End result, gold tones. But the argument it's the impurities doesn't hold water. A .999 coin would have 0.001 impurities. A .9999 coin would have 0.0001 impurities. Neither of those is a large enough quantity to even be seen by the human eye. So saying it is the impurities that are toning just isn't valid. Sorry my friend, gold tones, regardless of what science says.
No, I am a great believer in science. But I have generally found it foolish to believe what science tells you when your own eyes tell you that science is wrong. That is the qualifier