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<p>[QUOTE=&quot;-jeffB, post: 2007206, member: 27832&quot;]I wish I understood that better myself. I&#039;ve got a pretty good background in chemistry, but this gets into metallurgy, and a lot of stuff that I don&#039;t understand very well at all. (For example, chemistry alone doesn&#039;t explain why acid can raise dates on nickels -- it has to do with the crystallographic structure of the metal and how it flows during striking.)</p><p><br /></p><p>The effect you see here is especially confusing, because nickel is actually <i>more</i> chemically active than copper, and as a naive chemistry geek I would expect the nickel to go away <i>faster</i> than the copper. That&#039;s not what happens, though. Nickel seems to be especially good at &quot;passivating&quot; -- forming a protective skin that prevents further corrosion -- but that depends heavily on what&#039;s attacking it.</p><p><br /></p><p>One of our members, [USER=17261]@BadThad[/USER], is a metallurgist and chemist, and may be able to explain better how this happens.[/QUOTE]</p><p><br /></p>

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