I've been doing a lot of research about cleaning / preserving copper coins lately, but still aren't entirely clear on a lot of the condition issues facing copper coins. Here are 3 coins that seem to exhibit different condition issues. Can anyone tell me what the issue is (bronze disease, verdigris, corrosion?) and what the best method is for treating it? To be clear, all coins were submitted to one or two dips in hot peroxide, which I've found to be very effective. However, issues remain (that may have even been caused by the peroxide, I don't know) and I'd love to get more information about them. Thanks!
First of all, peroxide is an oxidizing agent and the process you are wanting to arrest/reverse/minimize is oxidation. Totally wrong approach. What would be good is a reducing agent and I really don't know that many common ones. Most copper cleaners depend on oxallic acid which whii reduce the copper oxide back to copper and give carbon dioxide. You can try dips made for silver, but I haven't had good results.
Hesitant to say this, and I won't say too much, but the trick to dipping copper (using conventional dips) depends on two things, well 3 actually. The first thing is it depends on what you are trying to do. For example, are you trying to remove extensive verdigris like with the OP's coins, or are you trying to remove toning on an MS coin to make it red again. The second is in finding the correct dilution of the dip and what you dilute it with, and then neutralizing the dip. And the third is in allowing the coin to stay exposed to the air for a few days so that the coin regains a somewhat natural color. It's not an easy thing to do, but it can be done.
Which is the coin exhibiting the extensive verdigris? The middle one, right? In this case, I'm really just trying to determine the type of damage to each coin so I can research the correct methods of cleaning/preserving/whatever.
It may be verdigris on all of them, but in any case I would say the one on the left is the worst. But all 3 coins are definitely damaged, and damaged to the point that it doesn't much matter what you do to them. Honestly if I were trying to remove the verdigris, PVC residue, or whatever it is, on those 3 coins, I'd just dip them and be done with it.
If you see green/blue-green on a copper coin, it is verdigris. Generally, ancients excluded, removing heavy verdigris will result in an undesirable coin. Since verdigris is corrosion, it actually removes copper from the coin in order to form. Once removed, you will have pitting and other surface problems exposed. Yes, all forms of verdigris can be removed - however, the amount of damaged caused by the removal process from using peroxide, acids, etc. end up being a bigger problem than the corrosion itself. You have to weight the benefit of removal versus the end-value of the coin. With common, modern coinage it's usually not worth the time and effort (for most coins) since it's more economical to simply replace a heavily corroded coin.
Green on copper can still just be PVC residue Thad, that's about the only exception I know of. And if you just leave verdigris alone, eventually it can completely destroy the coin. And while I agree that most times it's not worth the effort to remove it once it's become severe, at least its removal can save whatever is left of the coin.
Thank you. The one on the right appears to be more like corrosion (stuff that can actually be picked off the coin). Any tips for that? It's an 1857 in otherwise great condition, and potentially still holds some value. BadThad- you say that all forms of verdigris can be removed... how? I'm familiar with your product for removing light verdigris, but what about the heavier stuff? Again, I'm aware of the risks with valuable coins, but I'm just trying to experiment and learn with some common coinage.
Because the acid in it is reacting with the copper. When PVC residue is first deposited on a coin it is a clear, oily like substance. But in time it turns green due to that reaction. But at that point it isn't verdigris yet, it is still oily, slimy. Later after it dries, yeah I agree it can turn into verdigris, but it doesn't always do so. PVC residue can dry clear, or green, or tan, or even dark brown. Verdigris on the other hand is always green.
I suspect that if the residue is oily, you are probably seeing the plasticizer in the PVC (used to be dioctylphthalate, not sure what anymore). If the goop starts making a reaction with the copper, it is most likely due to the presence of dissolved HCl (hydrogen chloride - when dissolved in water we call it hydrochloric acid) and the goop can be colored green since it is one of the copper chlorides.
Good Evening All, I have a question hope maybe i can get some help; Ive been collecting coins just recently, and ive come across some interesting coins. That past few weeks ive been putting aside some lincoln cent coins in which have been very distinctive than many others ive been collecting, these lincoln coins, well mostly from 1968,1969 and some 1970's have a very odd color that helps me pick them out of a batch of lets just say 100 coins, thats how distinctive they are to the eye. with a bright yellowish orange(y) look. very shiny, and luster color. All letters in tacked some more bold than others as if they were dipped over again. Does anyone know what it may be? why that distinctive color? Has anyone run into the same coins?? Curious to know.
Ruben there are a great many possibilities. It could be something as simple as the coins being left in a jeans pocket and run through the washing machine to the coins being dipped - and everything in between that. There simply is no way that you could ever pin the cause down with any certainty.
Thanks GD, i quiet understand what your saying, its just weird that there only the 1968 and some 1967's. Ive picked a few without even checking the mint date. Just by the color im able to pick them out. Then to top it off, the mint year, and all letters seem to be all clear without any fade.
1968 was the last year for the obverse master hub. At that point, the hub was so worn that the dies produced from it had a dished appearance and the outer devices were getting very close to the rim. I believe the strike and the particular planchets they used made the 68's look a little different - especially when compared to 1969 and later after they made a new master hub. I suspect your not only seeing a color difference but also the overall look of the coin. Another interesting thing, these coins seem to stay red a LONG time. I've pulled hundreds and surprisingly quite a few are still red!
