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<p>[QUOTE=&quot;-jeffB, post: 4416350, member: 27832&quot;]This is relevant to my interests, as I have a gold Kennedy with one or two copper spots. I&#039;ve talked about using it as a pocket piece so that I can have the lowest-graded gold Kennedy in existence, but I don&#039;t think I could bring myself to do it. <img src="styles/default/xenforo/clear.png" class="mceSmilieSprite mceSmilie11" alt=":rolleyes:" unselectable="on" unselectable="on" /></p><p><br /></p><p>I&#039;m assuming that &quot;copper spots&quot; in general don&#039;t get their color from copper <i>metal</i>, but from copper <i>oxide</i>. If that&#039;s the case, either electrolytic or acid treatments should remove the color. High-fineness gold (.999) shouldn&#039;t be affected by either one, although I&#039;d be nervous about physical marks from just <i>resting</i> a proof coin on aluminum foil, never mind any chemical activity.</p><p><br /></p><p>I remember stripping oxide off copper wire by heating it and then hanging it over hot methanol. You get a smell of formaldehyde and a bright copper wire. I thought about using the same technique on coins, but I&#039;m not sure exactly how hot you have to get the metal, and I&#039;m not comfortable heating coins that much. I also don&#039;t know that this vapor-phase approach would have any advantages over liquid soaks. It might be nice to &quot;fix&quot; a coin that&#039;s browned in its slab, but I&#039;m pretty sure you&#039;d need temperatures that would melt the plastic.[/QUOTE]</p><p><br /></p>

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