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<p>[QUOTE=&quot;GDJMSP, post: 2037461, member: 112&quot;]Yes, toning can corrode coins once it reaches it&#039;s terminal stage, but until it does, it does not. This has been proved time and time again by the millions of toned coins that have been dipped. Once dipped, there is no corrosion visible. A coin that has been corroded will exhibit porosity, a rough textured surface often accompanied by pitting. That is why when a die becomes corroded/rusted what you see on the coins struck by the corroded die are raised bumps of metal.</p><p><br /></p><p>The green corrosion you mentioned is verdigris. It is most often found on copper coins but it is also found on silver coins and even gold coins at times. But verdigris, while it can literally eat away at the the metal of a coin and can cause pitting, it does not always leave a rough textured surface or pitting behind once it has been removed. But the underlying metal may be discolored. That said, yes the TPGs will slab coins that do have small amount of verdigris on them. And verdigris is not always active, it is only active when there is moisture present. And since moisture can be all but eliminated with proper storage a small spot of verdigris or even several of them will just sit there doing no additional harm to the coin.</p><p><br /></p><p>As to the OP&#039;s coin, yes I do believe the coin was probably toned almost solid black at one time and then dipped. And yes I do believe that the toning caused the corrosion seen on the bust and very light traces of it seen in the fields. As to whether the remaining dark toning can still cause additional harm, if not stored properly yes it can. But it is the extent of the damage already done that matters, once the surface of a coin, or part of it, has become porous and or pitted then the coin is no longer gradeable for it has been damaged.</p><p><br /></p><p>Are there worse cases ? Yes, of course, many of them. But there are many lesser cases too, and even those are relegated to problem coin status, and by the TPGs also. With the TPGs it all depends on what coin it is. On some coins even the tiniest bit of corrosion puts the coin in a problem coin slab. On other coins, the entire coin can be covered with corrosion and yet it is still slabbed cleanly.</p><p><br /></p><p>And yes there are all sorts of excuses and explanations given for this by the TPGs and those who have a seemingly blind faith their judgement. But since long before the TPGs ever existed it was and still is basic numismatic policy that once corroded, a coin, any coin, is no longer gradeable.[/QUOTE]</p><p><br /></p>

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