David M. writes: What is the consensus on dipping silver coins. My coin dealer says that it is OK if done properly? What do you think?
The coin dip that is used most often contains a mild acid that removes the top layer of silver from the coin; that’s how it removes “tarnish”. A small amount of the mint luster is also removed each time the coin is dipped. Mint luster is an optical effect caused by flow lines that are established by the striking pressure of the coin press. Since the flow lines are on the very top surface of the coin, dipping gradually sends your uncirculated coin toward AU or lower status.
There is another reason that dipping coins is destructive to them. Natural patina, the kind that takes many years to establish, is an oxide coating that can protect the coin from damage to pollutants in modern air. If the coin has been lucky enough to have achieved its patina originally and it’s surface has remained unaltered from the time of minting, the oxide coating actually contains oxygen from the air of that period. Dipping removes that protection and actually makes the coin more likely to oxidize quickly and unattractively. The “fix” only lasts a short while, forcing one to dip the coin anew, each time damaging the coin further.
My suggestion is to only purchase coins that please you. If you don’t like patinated pieces, stick to ones that have achieved a clearer oxide coating (they do exist and pros can tell the difference). If the coin needs surgery, don’t get involved.