Hey folks! I have a 1799 draped bust dollar that i have owned for 5 years (building a date set) it is a strictly original coin graded vf 25 by pcgs, and it matches well with the other coins in the set. The reason for my posting is i have a question for other collectors out there. On the obverse, to the right of the date, there is an area of a greenish crust. This spot has been there since the coin was purchased, and it does not appear to have changed in the years i have owned the coin. My question is should i be concerned? And....what is this? Is it old dirt, verdigris, or pvc? I sent a scan to a numismatist at heritage, and he said it was simply patina, and to keep the coin in a dry place free of sulphur (which it is). What should i do?
It is light verdigris from the copper alloy in the coin. There is nothing "blooming" in the verdigris and it seems pretty inert. Given that the coin is encapsulated it should remain that way.
If it is completely unchanged in five years, @scottishmoney is likely correct. Were it a PVC problem, it would almost certainly have progressed - being the "active" green color of the manifestation - in both size and likely damage to the coin. What it isn't is "patina," either way.
In numismatics, and other walks of life, patina is often used to refer to more than one thing. Toning, or color is one of them. But I assume that you said what you said because of what ancient collectors are referring to when they use the term. And yeah, I agree, it has a different meaning for them. But that doesn't mean it is inappropriate to use when talking about other coins.
I have the impression of "patina" as some natural chemical aging process related to interaction of atmospheric chemicals with the metal of the coin. This is either verdigris or PVC plasticizer reaction, neither of which fit my definition of "patina" the same way a human injury doesn't fit the definition of "aging."
If you are referring to the green spot, and only the green spot, on that specific coin, I would agree with you - it is not patina, it is verdigris. But the rest of the coin is covered with patina - toning. However, as I mentioned above, if you talk to an ancient collector, verdigris, once it has become hard, is specifically referred to as "patina". So, the guy at Heritage who referred to the spot as "patina" may have done so for that reason. That's really all I'm trying to point out.
Yes, that particular spot is what I was addressing since it's what the OP called out. Beyond that, we're in complete agreement. Any "encrustation" which hasn't consumed a coin completely in two millennia is acceptable.
Doug is correct. In fact, @SuperDave has posted a great definition of "Patina" illustrating an understanding of the subject: "I have the impression of "patina" as some natural chemical aging process related to interaction of atmospheric chemicals with the metal of the coin." He has just described toning (a type of patina) and that's what the gray colored "patina" is on the dollar. I was taught that ANY oxidation, including corrosion such as RUST, can be considered to be a coin's "patina." However, we don't associate/use such an "artful" word in cases of terminal corrosion. :D As Doug wrote, the word is mostly used to describe the greenish surface found on ancients. Collectors even describe the color of the finish on old wood using the word "patina." For that reason, members may wish to expand their thinking about the term. Finally, the green on the dollar is not patina. It is a spot where surface corrosion is beginning. It should be removed before it eats into the surface. The coin needs conservation. I know that at least one of the secondary TPGS (ICG) would have contacted the customer for permission to remove the contamination (for free) before slabbing the coin.
In context of silver coins, I equate patina with the original luster of the uncirculated coin, slick to the touch, with or w/o toning. Maybe my definition is too restrictive.
It's not too restrictive in the context of "modern" coins, let's say an arbitrary 375 years old or newer, post-hammered. Whatever that date is, after it I couldn't consider any effect able to be measured in a third dimension (above the molecular level) to be "patina." With Ancients, as Doug mentioned, those rules change.
