For some time ago I spoke with an experienced conservator employed by the university and museums. We spoke about the so-called “Bronze Disease”, and I had some questions. Here is what I’ve been told by the conservator: A cobber coin in earth will consist of a base metal, 3 layers of patinas and lastly a layer of dirt. The patinas are layered in this order: black, red, green(blue). However, the layers of patina on coins are uneven, and that is why your coin can have different pockets of different patinas based on how deep they are cleaned. There is a difference between green patina and the so-called “Bronze Disease”, which is feared among coin collectors for no reason: Green patina is, as mentioned, just a patina. Green patina has dark color and is smooth. The so-called “Bronze Disease” is actually copper chloride. “Bronze Disease” has a bright color and is crusty, which can fall of if you scratch it. Why does the so-called “Bronze Disease” appear? Because the copper comes in contact with sweat, soil, cooking or moisture. Then it will make the so-called “Bronze Disease”. The so-called “Bronze Disease” is actually made by the copper, and it will sprout through the patina(s). So, basically, if you have sweat on your finger, and you touch the coins, theoretically you can create Bronze Disease. However, the “Bronze Disease” is actually NOT contagious. It cannot spread. I asked the conservator whether his other colleagues agree, and I was told that any serious schools of conservatory across the world agree that it is not contagious. Basically, if you have 90 copper coins without “Bronze Disease”, and you put it in a tray (or even a bag) with 10 other coins with “Bronze Disease”, then it will not spread. Because copper chloride is not contagious. So, if any of you are well-informed on this topic and is convinced that what I've written is nonsense, please tell me. And if you particularly is convinced that “Bronze Disease” is contagious, please tell me also.
Not all green patinas are dark, but I guess it depends on what you mean by dark. When compared to bronze disease, yes, but there are some beautiful lighter green patinas as well.
Does it not spread to other parts of the coin, such as the interior? I'd like to hear from others on this topic.
AFAIK there are patinas and there is Bronze Disease. Bronze Disease is light and flaky and if the chloride from one coin with it comes into contact with other copper coins it can "spread".
Yes, bronze disease can be very aggressive and sometime appear almost overnight. It is very distinctive, white to a very light green, and, above all, powdery. I've noticed that it also has a metallic odor, which is not surprising. This is active corrosion at work, a totally natural process but not one that bodes well for the coins we try to preserve, and it will over time totally eat away the coin's surface. Also, it will spread to other bronze, copper or brass coins. Coins with BD should be kept separately from other coins, especially if they are on a tray or otherwise in contact with each other. Bronze disease, base on my experience can be treated, or at least mitigated by neutralizing the corrosive process. This is achieved through the used of a distilled water bath, extended with changes of water is needed, as a first step, followed by a thorough drying in a low temperature oven. Then the coin needs to be left out and observed over time for any signs of the disease cropping up again. If that happens, then either a repeat of the distilled water is necessary, or, if it is very deep, the use of a solution of sodium sesquicarbonate and distilled water might be needed. However, this chemical will remove virtually all patina along with the BD if left unattended, so monitoring is essential. Some collectors try to seal the coin with Verdicare or Renwax. I haven't done that with the coins that I've had to treat, and so far so good. If you live in a high humidity climate, something that is becoming common even in more traditionally drier regions, then the treated coins would benefit being stored with some silica packets. Here's a link to a much more detailed description on steps to treat BD with a solution of sodium sesquicarbonate and distilled water: https://www.forumancientcoins.com/numiswiki/view.asp?key=bronze disease treatment
@robinjojo The conservator advised against cleaning ”bronze disease” with chemicals. In case one person wanted to get rid of ”bronze disease”, it was suggested to remove ”bronze disease” with scalpel/brush, and this process would take maybe hours. And once it is removed one should seal it with benzotriazole and incralac. And even this treatment will not protect the same coin from further ”bronze disease” if it is exposed to the same thing(s) as before (contact with sweat, soil, cooking or moisture). It will be interested if someone with proper education, that is one not getting his/her knowledge from internet, could give us some insight. I mean the internet and threads are filled with contradictory “advices” about the topic.
You are right. I made a mistake. Green patina can be darker and brighter. "Bronze disease" is typical (always?) brighter.
It seems to me that members are tending to give "life abilities" to metals that they see as spreading. Bronze Disease or copper toning will never happen with out water in a liquid or gaseous stage as the actual initial cause of various.If you live in a relatively dry area ( as I do in a desert ) you will never experience such. If you are in a wet area , but put your copper in a sealed container dry and never open it , it will not show any change. There are several other chemists on the forums who might have variations. IMO, Jim
Some bad advice and incorrect notions here :-( The problem with bronze disease is that this particular type of corrosion acts somewhat like a zipper: the offending molecules disrupt the metal surface then free themselves to latch onto the next, disrupting the atomic lattice like a cue ball blasting through a rows of balls. Many types of corrosion can be halted once you cut off the supply lines of the corrosive agent or you introduce a neutralizing chemical. With BD though the reaction is self-propagating because all it needs to continue is a fresh supply of copper and water vapor. This is why immersion in water is ineffective. In practical terms water vapor is nearly impossible to get rid of. Short of hermetically sealing the coin in an impermeable container it's hopeless to attempt to arrest the damage. The only effective method is to dig under the chlorides by exposing the copper core and only then applying something like benzotriazole or RenWax or whatever. For BD to begin you generally need three things to occur: salt, humidity and prolonged contact time. It is not true that merely handling your AEs with sweaty fingers will spell doom. While sweat does have dissolved salt, and obviously plenty of moisture, you're still missing the third factor of extended time. This is because, if you remember from your chemistry class, NaCl is a very stable molecule given the intense bonds created from these two elements. You would need a very rare set of conditions under which those two atoms would 1) momentarily let go of each other and, 2) for the sodium ion to preferentially attach to some other atom and not immediately retake the chlorine one. Only then would that Cl be free to attack copper and begin the destructive process. It's far likelier that the instances of BD happen as a result of halogenated compounds degrading as these provide a more plausible route for the release of those highly reactive atoms. Summary: if you're unlucky enough to get a coin with BD 1) scrape the lesion down to bare metal 2) clean the area with something like 35% concentrated hydrogen peroxide 3) optionally apply a protective barrier-forming film. Or just let it tone naturally. If the cleaning job was successful the chances of it reoccurring in normal conditions are very low. Rasiel
The conservator told me that sweat on fingers, after touching the coins, theoretically could create Bronze Disease, and even suggested to use finger latex like this:
Medical gloves cover the complete hand and will prevent leaving moisture on the coin, If it is a very precious metallic material, an absorbing facial mask will help a lot also in breathing. Its the water basis that can cause the problem whether it is a sneeze, talking or coughing over your activity or walking in the rain or a high moisture in the air. Using warm filtered air from a blower should prevent any reactions, IMO. Jim
Does this quarter have green patina? It has some copper color on the reverse. It is not flaky. It is very smooth and shiny. I've done some research, but have not seen any this smooth and shiny!? Where it appears flaky, it is very smooth.
So, what you are saying is it is not bronze disease!? I guess I knew the answer, but it looks like paint.
Hadn't considered paint, could be. First give it a hot water soak overnight or for a day or so and then (after dry) give it an acetone soak/bath.
