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<p>[QUOTE=&quot;Burton Strauss III, post: 2535732, member: 59677&quot;]The copper-nickel in a nickel is an alloy - ideally a uniform mix of copper and nickel atoms. If the mix is not quite uniform, over time as the coins surface ages, you get visible effects. The most common of these is in the Lincoln cent (pre 1982 when they were 95% copper) where you see the &#039;woody&#039; effect (the coin really looks like it has wood grain) - see here: <a href="https://www.cointalk.com/threads/got-wood.65353/" class="internalLink ProxyLink" data-proxy-href="https://www.cointalk.com/threads/got-wood.65353/">https://www.cointalk.com/threads/got-wood.65353/</a></p><p><br /></p><p>Another facet of coin minting you need to be aware of is &#039;work hardening&#039; - basically as you work a metal object (including striking it with dies to create a coin) the metal crystals heat up and harden. In order to be struck, the metal needs to be softened in what is called annealing.</p><p><br /></p><p>When the blanks are cut out of the sheet of metal, and the upsetting machine creates the initial rim, that causes the metal to harden and so the coin blank is annealed before being struck.</p><p><br /></p><p>If the annealing isn&#039;t properly done, copper atoms migrate to the surface of the coin. This makes the surface a higher % of copper (and softer) and the interior more nickel (and harder). This can cause some outlandish effect, see <a href="http://www.error-ref.com/improper-annealing/" target="_blank" class="externalLink ProxyLink" data-proxy-href="http://www.error-ref.com/improper-annealing/" rel="nofollow">http://www.error-ref.com/improper-annealing/</a>.</p><p><br /></p><p><br /></p><p>However, the most common cause of color changes in coins is exposure to something in the environment - usually coins found in the dirt.</p><p><br /></p><p>The colors&nbsp; you see on the surface of a coin are from thin films of oxides and other compounds. As light strikes the surface, it bounces differently from the oxide and the non-oxidized atoms. This is most common in silver coins (and can be amazing to see - <a href="http://www.jhonecash.com/research/toning_physics.asp" target="_blank" class="externalLink ProxyLink" data-proxy-href="http://www.jhonecash.com/research/toning_physics.asp" rel="nofollow">http://www.jhonecash.com/research/toning_physics.asp</a>). But it happens in nickels - you see golden shades, purple, even a few magentas.</p><p><br /></p><p>Unfortunately, most exposed nickels get ugly grey. That&#039;s what you have here. A coin that was exposed to environmental factors for a while and then found and continued to circulate until you found it.</p><p><br /></p><p>The give away? Look at the reverse, the fresh gash under the right hand and the ding on the top of the E in E Pluribus. See the exposed unaffected metal? See other dings and gashes that happened before the exposure and how they are uniformly grey?[/QUOTE]</p><p><br /></p>

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