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<p>[QUOTE=&quot;BigsWick, post: 117383, member: 3534&quot;]Carl,</p><p><br /></p><p>Thanks for the chemistry lesson! I believe the closest powerplant to me is a nuclear one in Idaho, so I doubt that&#039;s it- or at least I hope not! There are a few pools around, but none near me. Our water table does have a lot of sulfur in areas and there is typically little humidity.</p><p><br /></p><p>I think the dark area is simply a carbon/copper spot (I&#039;ve heard both terms used) that has probably been on the coin for years. It is roughly 1/16 of an inch in diameter. Is that considered big for a carbon/copper spot?</p><p><br /></p><p>My understanding is that they come from concentrations of copper in a given area of the coin, the result of a weak mix of the copper/gold. The spot doesn&#039;t appear to be &quot;growing&quot; so I guess that is good. Maybe the other two spots are where the coin is starting to tone, but I might have to wait several years before I find out for sure.</p><p><br /></p><p>Like some collectors new to slabs I did think the first few slabbed coins I bought were airtite, but I soon found out that they weren&#039;t from members of another coin forum. I&#039;m not sure about this, but one of them even claimed that the process used to seal most slabs would create bond that was only good for about 10-15 years. That sounded a little suspect to me, but&nbsp; I&#039;ve never owned a slabbed coin that long so, again, I&#039;ll have to wait and see- but I doubt it.[/QUOTE]</p><p><br /></p>

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