Numismatic and History Discussions > Ancient Coin Forum

Spread of Bronze Disease - any definitive answers?

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Elias G:

So I've read extremely conflicting information, and received extremely varying answers. This seems like a topic that people do not agree on, but surely some definitive answer exists (i.e. not "my experience has been...", but rather "chemistry says...").
How easily does bronze "disease" spread?

a) Is remaining direct contact needed? (I.e. does contact between "infected" and "healthy" coin need to last for extended periods of time)
b) Is it enough that larger flakes/multiple specs of bronze disease end up on a healthy coin? (Which can be expected from brief direct contact between coins)
c) Is it enough that singular small specs of bronze disease end up on a healthy coin? (What can be expected from indirect contact, such as touching bronze disease coin then touching healthy coin)
d) It does not spread between coins.

Also, does bronze disease infect coins with >75% silver; i.e. will romans from before 175AD get bronze disease?

Would love some solid information on this. At the moment I am treating a, b, and c as being "true", meaning I am cleaning surfaces between each possibly infected coin touching or getting close to them, washing my hands and tools between touching coins, and storing infected coins 10ft away from healthy coins. I am even keeping coins in mylar flips far away from any BD coins, so not even a single particle of BD can sneak into the flips. My guess is all of these practices are completely unnecessary; which would be pretty great.


PS: Some of those conflicting sources: ("Thankfully, it does not spread from one coin to another" - option d) ("Bronze disease can be transferred if the coins come in contact with each other" - option a and maybe b) ("can't actually jump across from coin to coin without those two coins either touching or being jostled around to make flakes of the green stuff break off and land on other coins" - option a, b and maybe c)

Hi EG,

Bronze disease definitely does spread between coins. And they only need to be in close proximity to each other. They don't need to be "touching" (in direct contact with each other). The theory is that the HCL gases/vapors infect the healthy coin. Being in a closed/sealed environment accelerates the process.

It happened to me. I store my coins in mylar flips, which are stored in blue plastic coin storage boxes.

A few years ago, I wrote extensively here in Forum about my experiences regarding bronze disease and my treatment of it.


Elias G:
The whole "in air" spread is also something I have seen wildly conflicting information about. Some saying it actually takes thousands of years to develop the initial stage in soil. Even saw a post of a guy trying to quickly infect coins, to no success.
How many coins did you get infected this way? Were they from the same hoard?

While this certainly is alarming, it does not really imply that singular grains of BD actually can/will infect other coins. Very different situation with fully airtight environments (one that I assume most people do not have).

EDIT: Here is the thread of the guy trying to recreate BD;

EDIT 2: This spread was from very longterm storage in a sealed box, without opening the lid - correct? Not just coins in a cabinet? Feel like if they were in a cabinet those gases would dissipate pretty quickly, since it is not fully sealed. Also does not seem like people really agreed on if the coins actually infected eachother?

Hi EG,

One of my coins had a very severe case of BD. It spread to 2 other coins. Those 2 coins were immediately next to the infected coin in my blue plastic coin storage box. Of course, the coins weren't "touching." They were separated by several layers of mylar.

They were not from the same hoard.

They were stored in a sealed plastic box for about 10-15 years, but the lid was opened numerous times.

Here is a link to my website page containing those coins:

The second coin in that page is the coin that initially had severe BD. It (the HCL gases) infected the coins immediately next to it in my storage box. Those are the first and fourth coins in that page. The third coin in that page was added at a later date.


I think that certain coins with a high amount of chloride impurities in the matrix of the flan will always be highly susceptible to bronze disease, especially in the presence of moisture or high humidity.  So, not much you can do about it other than what we are already doing, just isolating, treating and keeping an eye on them.  These impurities are either naturally occurring or introduced during the refining and casting process of the flan.  Coins composed of a purer copper alloy will likely be more stable and less at risk.  When I have a coin with just a small spot of BD I try to clean out the pit mechanically down to clean metal and add a small drop of clear neutral mineral oil to prevent any further moisture entering.  Most of the time it seems to work.


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