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<p>[QUOTE=&quot;-jeffB, post: 3238300, member: 27832&quot;]It seems to me that the jury&#039;s still out on &quot;toning forms a protective barrier&quot;. If that were the case, I wouldn&#039;t expect to see so much rainbow toning -- the parts of the coin that start to turn would be protected (and stop turning), and the parts that hadn&#039;t yet started, still unprotected, would catch up.</p><p><br /></p><p>I have assumed that a silver sulfide layer doesn&#039;t <i>passivate</i> much at all, but I don&#039;t have the materials-science chops to back that assumption.[/QUOTE]</p><p><br /></p>

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