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<p>[QUOTE=&quot;yakpoo, post: 1091735, member: 18157&quot;]I would be bragging if I tried calling myself a &quot;Novice&quot; in this area...but I find it intriguing. I see three (3) possible sources for the toning/spotting (ordered least likely to most likely)...</p><p>&nbsp;</p><p>1. A chemical reaction with Gold,</p><p>2. A chemical reaction with residual compound within the Gold alloy, or</p><p>3. A reaction with a non-alloy substance that is either on the surface of (or permiates) the metal.</p><p>&nbsp;</p><p>I find it hard to imagine gold as the reagent. What percentage of gold coins (in your experience) exhibit &quot;toning&quot;? Is it as common as with silver coins? If not, I wonder if there could be some residual contaminates left over from the refining process.</p><p>&nbsp;</p><p>I was reading about the <a href="http://en.wikipedia.org/wiki/Wohlwill_process" target="_blank" class="externalLink ProxyLink" data-proxy-href="http://en.wikipedia.org/wiki/Wohlwill_process" rel="nofollow">&quot;Wohlwill&quot; gold refinement process</a>. The Wohlwill process uses Aqua Regia (a 1:3 solution of Hydrochloric and Nitric acids) to produce Chloroauric acid. Chloroauric acid is used as the electrolyte in the Wohlwill electrolysis process to refine 99.999 pure gold. The Wohlwill refinement process has been in use since 1874. </p><p>&nbsp;</p><p>An older refining process (the Miller process) is also used to refine gold to a 99.95% purity. The Miller process uses chlorine gas to react with (and precipitate) impurities from the molten ore.</p><p>&nbsp;</p><p>It seems like Chlorine is the common element to both processes. If there was some residual chlorine left in the gold, I wonder if it might react with sulpher over time to produce sulpher dichloride...which, in it&#039;s purest state, is a &quot;<span style="color: red">cherry red</span>&quot; compound. :scratch:[/QUOTE]</p><p><br /></p>

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