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#1
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corrosion pits happening suddenly on uncirculated large silver coins
I have been finding that some of my uncirculated world crowns develop
sudden corrosion pits and I don't know the cause or what to do to stop further damge. These pits are definitely into the coin surface, not just spots or toning on the surface. The coins are stored in non-PVC safe-T flips, once they were in PVC flips but after some years I changed the flips and cleaned any possible PVC residue with acetone. I have seen this problem develop on perhaps 5% of my bright uncirculated crown coins which I have owned for years. The affected coin might be fine for years (I look at my coins closely and often), and a few weeks later suddenly develop a pit or two. The corrosion spots are cone-like depressions only a millimeter or so, frequently with tiny red/brown centers, sometimes there are tiny lines radiating out. Usually only one or two per coin, they aren't on the high points, more often in the field randomly located. Once affected, the coin doesn't necessarily develop more pits. They aren't associated with any green on the coin. I can't see any associated residue on the holder that might cause it, or on the coin. A scary problem unless I can figure out how to prevent these for the future. The coins are bright white, have been dipped in the past, still very bright. It only seems to happen with white uncirculated coins, particularly crown size, not on toned coins or copper. Anyone seen this before or know what causes it or what to do to prevent? I have never seen this problem anywhere in the coin literature. |
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#2
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corrosion pits happening suddenly on uncirculated large silver coins
My guess is that this is related to condensation somehow. That is, moisture is condensing out of the air due to temperature drops and focusing toning/corrosion at that point. My advice is to keep the coins at a constant temperature (room temperature) and reduce humidity with a dehumidifier or silica gel. Perhaps Intercept Shield holders would also be effective, but not I think if the coin is in contact with tiny water droplets. Bob Leonard |
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