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<p>[QUOTE=&quot;qwasty, post: 986883, member: 27130&quot;]That equilibrium is exactly what prevents the gold &quot;oxide&quot; from completely consuming the entire coin. Equilibrium probably occurs before the reaction products can even cover the surface with a single layer of molecules. That single layer would be invisible. With less than that, you can bet that it would be hard to detect even with sophisticated scientific instruments, let alone with the eyes of the average non-scientist coin collector.</p><p><br /></p><p>Others have already said it, but I&#039;ll repeat it just for completeness: The few gold molecules that may exist on a coin in natural air are so rare that they are of no practical importance to coin collectors. You definitely, absolutely, 100%, never, ever, could EVER possibly see them.</p><p><br /></p><p>With that said, yes, your speculation is right. It WOULD change the surface, but not enough for anybody to notice. After a few hundred years, it might be detectable with an electron microscope though. The effect your talking about is the same as the &quot;crystallization&quot; effect of ancient silver coins. Basically, the silver doesn&#039;t so much crystallize (since it was always crystallized) as the crystallization becomes apparent as the impurities get dissolved away by the wind and water:</p><p><br /></p><p><a href="http://www.forumancientcoins.com/moonmoth/crystal_coins.html" target="_blank" class="externalLink ProxyLink" data-proxy-href="http://www.forumancientcoins.com/moonmoth/crystal_coins.html" rel="nofollow">http://www.forumancientcoins.com/moonmoth/crystal_coins.html</a></p><p><br /></p><p>With the impurities gone, all that&#039;s left is the silver crystal structure. If something similar happened to gold, which I&#039;m sure does happen, then the textured remaining surface would have lots of microscopic nooks and crannies for invisible debris to collect. Enough of that debris, along with the changed texture of the coin, will make the coin surface less reflective, and thus, it will appear to be &quot;toned&quot;.</p><p><br /></p><p>Although gold doesn&#039;t have the same crystalline nature as silver does, which is why ancient gold coins don&#039;t suffer from &quot;crystallization&quot; problems, I&#039;m sure the effect is there to a much smaller degree. It may or may not be visible, but I would be surprised if it weren&#039;t visible, since we can see red spots just fine.</p><p><br /></p><p>Either way, I&#039;m sure plain old fingerprints are much more likely to have a prominent &quot;toning&quot; effect than any of these more complicated processes.[/QUOTE]</p><p><br /></p>

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