Can it be determined wherher a coin has bronze disease from photos alone?

Hi everyone, I just started collecting ancients a few months ago so I’m still new to the hobby. I’ve learned a lot from this forum, and wanted to ask whether it is possible to determine whether a coin has bronze disease from photos alone.

For example these two coins. One has a lot of bright green showing, and the other has some green in the areas of porosity, and from what I’ve read that can be a sign of a recent attempt to clean off the physical evidence of bronze disease. I have no idea if these are just harmless hard deposits though

https://images.vcoins.com/product_image/294/7/7Poz9r9H2nLtki4SQZk86B4xG5cDfe.jpg

https://images.vcoins.com/product_image/294/Z/zZ44Ex5a9Tgp5n7R3FbLjr8Qd6KwSk.jpg

Is it expected that vcoins sellers would disclose if a coin has BD? Or is it assumed the buyer would make the determination based off of photos? Is it fair to directly ask a seller whether a coin has BD or is that not appropriate?

Appreciate the help

 

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I don't see BD on those coins. Hard green deposits on one, porous surface on the other. That porosity is, of course, caused by corrosion, but not necessarily the kind of fast-moving corrosion we call "bronze disease."

For dealers, how/when to report corrosion can be difficult. The question is always what counts as "active" corrosion? or corrosion likely to resume in the future?

Generally, though, if there's full-blown, active "bronze disease," yes, you would expect it to be reported. Many dealers disclose when a coin has been previously treated for bronze disease but stabilized.

 

Hello @Jlewis. Welcome to Coin Talk Ancients (and Medievals).
I'm not an expert in bronze disease. I've been collecting ancients and medievals for 5 years, but I've never really learned to tell the difference between stable green patina versus bronze disease. I usually don't worry much about bronze disease. I have many bronze ancient coins, and many bronze medieval coins. Many of them have green patinas, or areas of green patina. I've never had a coin, in which the green patina increased noticeably, while I owned the coin.
I have a small number of coins, which had a small bit of green patina, which looked unsightly to me because of the location of the green patina. For those few coins, I used a sharp pointy scalpel and a microscope, to scrape off the green patina. For 1 or 2 of those coins, I may have rinsed the coin with distilled water, and then wiped the coin dry with a piece of cloth, after I removed the spot of green patina. For 1 coin, I vacuumed the coin, using a drinking straw attachment, to ensure that I removed all of the little flakes of green patina which I had scraped off.
The 2 coins in your post, look okay to me. I've bought coins with similar amounts and similar types of green patina, and I've never worried about them.
I've never asked a dealer, if a coin for sale has bronze disease. It's not that important to me.
However, some ancients collectors are much more worried about bronze disease, than I am. Perhaps other ancients collectors, who are more knowledgeable about bronze disease than I am, will reply in this thread.

 

sometimes

 

It is a silly nomenclature if I ever heard one. It is not a "Disease" , it's a common chemical reaction that needs a metal like copper, moisture ( which may not appear as liquid water) and medium to high temperature. It is what people with non-ancient coins call Verdigris. If the coin is put into an air tight capsule, flip. etc.there should not be verdigris. If a person doesn't like capsules or flips, put them in a box or container lined with sanded copper tape strips. They will turn green long before a coin. If the tape does start to change, just replace. it. Jim

 

Verdigris is not the same as bronze disease.

 

My understanding it that @RichardT is correct.

Everyone knows it is a chemical reaction, not a biological process. (Other fields of conservatorship have other biological disease analogies for the corrosion affecting their materials as well.)

The reason ancient coin collectors (and conservators of antiquities) use a different term from verdigris is because "bronze disease" is both chemically and qualitatively different.

I'm not a chemist, but my understanding is that the verdigris reaction produces copper acetate.

The so-called "bronze disease" reaction produces chloride salts.

(I guess we could replace "BD" with "CuCl2·3 Cu(OH)2 + 2 HCl" or, for short, we could start saying our coins are afflicted by "green cupric chloride/cupric hydroxide compound and hydrochloric acid.")

Removing it from oxygen is a good start. However, it's very difficult to seal out oxygen fully enough to completely halt the process, and then it can rapidly resume. There are cases of people claiming it appeared or progressed inside sealed slabs. (Anecdotally, Verdicare & other verdigris products don't help "BD.")

Qualitatively, "BD" / "cupric chloride" is so alarming because it can be a very rapid reaction and very destructive. Within weeks large portions of the coin can become powder. It isn't unheard of for it to "eat" holes all the way through a coin. (Even thick ones.)

Here's my most recent example (first in years, happily). As far as I could tell, it sprouted in just a few weeks since I last looked at the coin. Previously there was never any visible sign of this reaction. The pits underneath are deep.

Large photos so you can click & really zoom in:


I haven't seen that kind of powdery reaction product on modern coins. (And it never seems to affect fake ancients. Only ancient ancients.)

There's a guy at my local coin club who brought in a plastic jewelry box full of ancient bronze coins in 2X2 holders (some cardboard flips, some rigid vinyl, some were soft types full of plasticizer). He didn't collect ancients and hadn't opened them for 20 years. (I was there giving a presentation on ancients, so people brought what they had.) Maybe 1/3 to 1/2 his coins showed some degree of active corrosion. Several had turned almost entirely to neon green-blue powder and mostly crumbled when gently probed through the plastic.

For whatever reason, it only seems to affect ancient bronze that has been buried for centuries. Some people give explanations for the necessary reactions, but I don't know enough about the chemical processes to try to explain it.

 

In a previous life I worked as a low level conservator of metals. My issue is with the word 'disease' - because it fuels anxiety amongst collectors and implies things about it which simply aren't true. It isn't biological in nature and there is no evidence it can spread between objects as a virus or sickness might between people. The appearance of it on numerous coins or objects simultaneously is often 'symptomatic' of poor storage conditions than anything else. I just tend to call it active copper alloy corrosion and be done with it.

It is interesting what it affects, especially in recently excavated finds. The burial environment is often one possible root cause, as coins and objects tend to acclimatise to the conditions they become deposited in. I think particularly acidic burial conditions often sets a precondition.

 

Many people claim otherwise, including at least some professionals. I'm in a hurry, but just searching "bronze disease" and "contagious" I find multiple academic journal articles (whether they're high quality journals, I don't know) that explicitly claim it can spread from one object to another.

The usual suggestion is that the chemical reaction is perpetuated either through contact with physical particles of copper chloride or through hydrochloric acid in the immediate atmosphere.

I don't know whether anyone has attempted empirical tests of the chemical processes. And I agree that we should have the evidence one way or another before making a strong claim about it. But I don't see any a priori reason to assume it can't spread between objects or across different parts of the same object.

 

[QUOTE="But I don't see any a priori reason to assume it can't spread between objects or across different parts of the same object.[/QUOTE]
Exactly why I assume that it can.

 

It depends on the coin, how advanced it has spread and where it has occurred on the coin. Welcome to CT.

 

It's a chicken-egg kind of argument, to my eyes. Is one object 'infecting' the others, or is the fact that multiple objects are 'breaking out' a feature 'symptomatic' of poor storage and/or being excavated originally with high levels of chlorides in the soils where they once were deposited? Only carefully controlled experiments will tell for sure.

 

Bronze disease is not verdigris. Both involve copper salts but the carbonate salts of verdigris (e.g. malachite) can form a hard protective patina. Bronze disease, on the other hand, involves chloride salts. Bronze disease isn't a single reaction but a repeating cycle of reactions in which the byproduct of one feeds another until the object is completely consumed. Bronze disease can't be "cured" but the process can be arrested and prevented from recurring by depriving it of moisture, a necessary component. Transfer of chlorides from one object to another can spread the problem. A detailed description of the reaction cycle can be found here:
https://en.wikipedia.org/wiki/Bronze_disease