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<p>[QUOTE=&quot;desertgem, post: 983915, member: 15199&quot;]I couldn&#039;t access the full article as I didn&#039;t have subscription, so I do not know how they were produced. But the way it reads, one could not just go out and find the oxides in nature, they do have to be produced in a lab. Also in several of the readings you provided, they mention that the oxides rapidly revert to metallic gold in the presence of air. So how could they maintain themselves as a &quot;tone&quot; . If tone appeared at 10:30 and disappeared at 10:31, wouldn&#039;t it&nbsp; (1) be a great conversation topic on a coin forum, and we would have already heard much about it and (2) I haven&#039;t found a citation that describes the oxides as a color different from white/gray or gold. </p><p><br /></p><p>I understand that gold coins can show a toning. However, I find that when a scientific study shows the redness to be related to silver and not gold, and when studies of gold compounds such as oxides are rare and transient, I still have to go with the OP. I suspect it is a good chance that if a 500 yr. old toned gold coin was tested the same way that silver or copper compounds will be the cause. I guess that is the way I was trained. Thanks for an engaging discussion.</p><p><br /></p><p>Jim[/QUOTE]</p><p><br /></p>

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