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<p>[QUOTE=&quot;Info Sponge, post: 983156, member: 20538&quot;]There are gases in the atmosphere other than nitrogen, oxygen, water vapor, argon and carbon dioxide, in trace amounts. Gold could conceivably react with one or more of them to darken over time even though it doesn&#039;t form stable oxides. EDIT: one of those links points to stable hydroxides: there are trace hydroxyl free radicals in the atmosphere (trace only because they&#039;re highly reactive). Could darkening be gold hydroxide? That&#039;s speculation. And it wouldn&#039;t explain red spots.</p><p><br /></p><p>Relevant question: have there been any red spots on the .99999 maples? 10 ppm impurities is the lowest in coinage, at least that I&#039;ve heard of.[/QUOTE]</p><p><br /></p>

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