Do we worry too much about "bronze disease," or not enough?

[Ten-Speed]

I'm not sure if I worry too much about bronze disease, or not enough. I keep the coins in under-30 percent humidity, but I like to take them out and sometimes leave them out awhile.

First, terms: I'm going to use the term "green corrosion" instead of "verdigris" or "bronze disease."

Green corrosion refers to the light green and sometimes flaky/dusty spots/areas on coins. It's much lighter than the surrounding green patina. It may be hard to distinguish if there is an apple-green patina.

"Verdigris" is often referred to as being the final, desired patina on copper objects of art, etc. It is a protective coating and doesn't eat away at the object. At least, that's what I've been able to figure out from my readings.

"Bronze disease" is descriptive as it suggests the insidious nature of the green corrosion, but there's a chemical reaction going on, not a biological process with germs.

Do you have a philosophy regarding green corrosion on your coins?

If a coin obviously has green corrosion, will you still purchase it if it is rare or if it is a coin you need, i.e. hard-to-find variety?

Have you ever personally witnessed a coin with green corrosion significantly deteriorate while under your care?

What about "borderline coins"? I know that I will pass up on these and I know I've passed on nice coins by doing this.

Perhaps the best way to spot green corrosion is to ask a very experienced collector who can say, "I know it when I see it"?

Have you used distilled water or products such as Verdi-Care to treat green corrosion?

What is the best term to use?

Your thoughts are welcome and appreciated.

 

Edited August 11 by Ten-Speed

[John Conduitt]

Most green on coins is not bronze disease. Some lighter green areas on coins that look like bronze disease do not develop. Perhaps these are not bronze disease - indeed, how can they be, if the reaction does not develop? Can it be dormant? Even in dry places, there's enough moisture in the air for it to continue, but it doesn't. And if it is dormant and does not start again, does it matter?

But very occasionally, I have had a coin with bronze disease. You can't mistake it as the green areas grow quickly and are fuzzy. This happens even when there was no green area on the coin originally. I have treated these in distilled water but it takes a long time and more of the coin gets eaten before it is over. Harsher chemicals tend to also damage the coin to get rid of the chemicals that cause bronze disease, but at that point the choice is for there to be no coin at all. But because of that, you don't want to treat every coin with a green patch for bronze disease until you know it really is bronze disease.

I wouldn't buy a coin I thought had bronze disease. But green on a coin with no evidence of it having been eaten anywhere else is likely not a problem. It might be more likely that a coin with large pits in the surface had bronze disease that was cleaned off, and should be avoided more than a coin with a green patch. In any case, I never let any of my bronze coins come in contact with the others, since losing one coin is bad enough.

Edited August 11 by John Conduitt

[Salomons Cat]

First of all, I do not collect bronze coins at all.
But I think what helps here is a basic understanding of what bronze disease is. 

Here's wikipedia for the details:

Quote

First, copper is oxidized to copper ion: (1) Cu → Cu+ + e−

The copper ion reacts with the chloride ion to form the insoluble white salt copper chloride: (2) Cu+ + Cl− → CuCl

The copper chloride reacts with atmospheric moisture and oxygen to form a green copper chloride/copper hydroxide compound and hydrochloric acid: (3) 4 CuCl + 4 H2O + O2 → CuCl2·3 Cu(OH)2 + 2 HCl

The remaining copper is oxidized by air to the copper ion: (4) Cu → Cu+ + e−

The copper(I) ion reacts with the chloride ion in the hydrochloric acid to form the insoluble white salt copper(I) chloride: (5) Cu+ + Cl− → CuCl

The reaction then repeats itself from equation (3). It is the presence of two different white and green salts that give the flaky green appearance.

So, what causes bronze disease (or first, cuprous chloride) is chloride.
Where does chloride come from? It exists in tap water, although in many countries the concentration is very low. Chloride is also a natural part of sweat.
I would advise to never touch your coins with sweaty fingers. Gloves, coin capsules or even slabs make sense if you want to avoid bronze disease.

Edited August 11 by Salomons Cat

[Phil Anthos]

Not enough.

 

[John Conduitt]

5 minutes ago, Salomons Cat said:

First of all, I do not collect bronze coins at all.
But I think what helps here is a basic understanding of what bronze disease is. 

Here's wikipedia for the details:

So, what causes bronze disease (or first, cuprous chloride) is chloride.
Where does chloride come from? It exists in tap water, although in many countries the concentration is very low. Chloride is also a natural part of sweat.
I would advise to never touch your coins with sweaty fingers. Gloves, coin capsules or even slabs make sense if you want to avoid bronze disease.

Yes wearing gloves would seem a good idea. In theory, if your coins have a patina, they won't get bronze disease from being handled, but...

Capsules and slabs are not airtight, and allow in air and moisture. So I presume they can still get bronze disease. It would seem sensible to put coins destined for a TPG into distilled water first to neutralise the chlorides, but of course, water is one of the triggers to start bronze disease.

[ewomack]

With all of the bronzes I've bought in the past few years, I might not worry about bronze disease enough. Periodically, I try to check them (I don't have that many) for fuzziness or spreading of green areas. So far, I have had no emergencies. I also keep a bottle of Verdi-Chem on hand, though I haven't had to use it yet. I hope I never have to.

I keep my bronze coins, and most of my unslabbed coins, in 2X2 SAFLIPS, and then in Intercept boxes. I'm hoping that provides enough separation and protection for each coin. The coins stay in their flips, and so don't get handled with bare hands.

One particular coin in my pile probably qualifies as a "danger coin." This Justinian II has likely seen corrosion, or maybe bronze disease, in the past. So far, it seems stable, but I try to examine it once in a while. It was sent to me for inspection before purchase. We'll see if it holds out.

Justinian II (705-711), second reign, Æ Follis, Constantinople, Obv: Legend obscure, crowned facing busts of Justinian and Tiberius, each wearing chlamys and holding patriarcal cross set on globe inscribed PAX; Rev: Large M, cross above, Γ below, CON in exergue; 19-20mm, 3.81g; Berk-806, MIB-43, DO-12c, Sear 1428

Over the past few years, I have learned not to live in fear of green spots on coins. Many bronzes have them and the vast majority are probably stable. But, one never knows, so early detection can make a huge difference. Don't let bronzes sit in boxes unexamined for years.

[Salomons Cat]

50 minutes ago, John Conduitt said:

Capsules and slabs are not airtight, and allow in air and moisture. So I presume they can still get bronze disease. 

I still think that capsules or slabs significantly lower the risk of a coin to contract bronze disease (or, in other words, to get into contact with chlorides). Because chlorides are not a part of the air, even if it is humid.

50 minutes ago, John Conduitt said:

Yes wearing gloves would seem a good idea. In theory, if your coins have a patina, they won't get bronze disease from being handled, but...

Capsules and slabs are not airtight, and allow in air and moisture. So I presume they can still get bronze disease. It would seem sensible to put coins destined for a TPG into distilled water first to neutralise the chlorides, but of course, water is one of the triggers to start bronze disease.

I'm not sure how effective distilled water is to neutralise chlorides. I assume that it is a very careful approach that needs a lot of time.
I have read that for a localized treatment to extract chlorides, a solution of 5% sodium sesquicarbonate in distilled water is recommended. This would be, for example, 5 grams of powdered sodium sesquicarbonate plus 95 ml of distilled water. @Theodosius has tried this here 🙂

Verdi-Care seems like another option, although I have no clue what is in there. And they probably also don't want to tell it.

Edited August 11 by Salomons Cat

[John Conduitt]

7 minutes ago, Salomons Cat said:

a solution of 5% sodium sesquicarbonate in distilled water is recommended

From my experience, this is a very harsh chemical that can erode detail from coins by itself. So it would not be something to use speculatively, only when you definitely have bronze disease.

[Postvmvs]

As @John Conduitt mentioned beware of coins with unexplained pits. My only "infection" thus far has come with a pitted coin with no green corrosion. A few months after I acquired it, despite not handling and storing properly it was covered in the tell-tale powdery corrosion of bronze disease...

Dealer photo:

Same coin a few months later:

Edited August 11 by Postvmvs
add photos

[Ten-Speed]

3 hours ago, ewomack said:

With all of the bronzes I've bought in the past few years, I might not worry about bronze disease enough. Periodically, I try to check them (I don't have that many) for fuzziness or spreading of green areas. So far, I have had no emergencies. I also keep a bottle of Verdi-Chem on hand, though I haven't had to use it yet. I hope I never have to.

I keep my bronze coins, and most of my unslabbed coins, in 2X2 SAFLIPS, and then in Intercept boxes. I'm hoping that provides enough separation and protection for each coin. The coins stay in their flips, and so don't get handled with bare hands.

One particular coin in my pile probably qualifies as a "danger coin." This Justinian II has likely seen corrosion, or maybe bronze disease, in the past. So far, it seems stable, but I try to examine it once in a while. It was sent to me for inspection before purchase. We'll see if it holds out.

Justinian II (705-711), second reign, Æ Follis, Constantinople, Obv: Legend obscure, crowned facing busts of Justinian and Tiberius, each wearing chlamys and holding patriarcal cross set on globe inscribed PAX; Rev: Large M, cross above, Γ below, CON in exergue; 19-20mm, 3.81g; Berk-806, MIB-43, DO-12c, Sear 1428

Over the past few years, I have learned not to live in fear of green spots on coins. Many bronzes have them and the vast majority are probably stable. But, one never knows, so early detection can make a huge difference. Don't let bronzes sit in boxes unexamined for years.

I also keep the coins in 2X2 SAFLIPS, but I do like to take them out....

[ambr0zie]

Probably not enough. 

In my last auction I have bought a Pius sesterius, in quite decent condition, but I was a little concerned about possible BD because of the aspect of the coin. 

And my fear was justified - when opening the package I noticed the coin ... and some dust. The dust was a flaky part that was close to the edge and the coin simply disintegrated. Big pity. And I can't blame anyone directly - the house packed the coin correctly and I didn't drop it - it happened in the transport. It is now in distilled water for a week, I will leave it for another week and change the water every 2 days. I am still annoyed and hope I can stop the process. 

[rasiel]

After having handled literally hundreds of thousands of ancient bronzes I can confidently say this is something that only happens with extreme rarity. When it does happen it progresses rapidly and ruins the coin in a jiffy. You can see the damage grow from one day to the next. And it's a very obviously wrong type of green, not something that leaves any doubt on whether it is or isn't. This photo is one of those rare ones I caught. Note that the green stuff isn't merely adhering to the surface but actively pitting.

You don't need to do anything extraordinary to avoid this happening. If your fingers are not all sweaty you can handle them as much as you want without worry. Store them individually using any traditional method and that's all there is to it.

Rasiel

Edited August 11 by rasiel

[Ten-Speed]

Thank you for the excellent photo....

[Theodosius]

The main risk factor seems to be the relative humidity of the air where you live. I live in Florida where the humidity even running my air conditioning all year is around 50 to 55%. I would say about 5% of the ancient bronze coins I receive develop bronze disease after a while. Bronzes that look perfectly fine when I get them start developing the spots in a few months. I am probably treating 25 bronzes for bronze disease right now. I currently like coating them with verdicare and leaving them for about a year, changing the solution now and then. This does not generally affect the rest of the patina. Most of the time I'm able to save a coin, but there may be some pitting. I've had a few that were completely eaten up from the inside no matter what I did.

Really surprised to hear @Rasiel saying it is very rare. Maybe I'm just bad luck. Lol. Most of the affected coins I have came from group lots and were not expensive coins (costing $200 or more). Maybe there's a sorting process by dealers where coins with suspected bronze disease find their way into group lots?

The sesquicarbonate treatment can remove some patinas but it is pretty effective after a month of soaking with frequent changes. It seems like some bronzes have chlorides internal to them which are extremely difficult to get rid of. 

I always bake my suspicious bronze coins for 2 hours at 200° f after treatment and try to store them in airtight containers with desiccant packages. 

There's a lot of misinformation about how to treat bronze disease, including recommending using toxic and dangerous chemicals. If you live in an area where the humidity is typically below 40%, you may never have a problem. If you live somewhere that typically has higher humidity, you may have a lot of problems.

John

[David Atherton]

Yes, it is overly hyped. But then again, hypochondria is a problem too. 

[Ten-Speed]

18 hours ago, Theodosius said:

The main risk factor seems to be the relative humidity of the air where you live. I live in Florida where the humidity even running my air conditioning all year is around 50 to 55%. I would say about 5% of the ancient bronze coins I receive develop bronze disease after a while. Bronzes that look perfectly fine when I get them start developing the spots in a few months. I am probably treating 25 bronzes for bronze disease right now. I currently like coating them with verdicare and leaving them for about a year, changing the solution now and then. This does not generally affect the rest of the patina. Most of the time I'm able to save a coin, but there may be some pitting. I've had a few that were completely eaten up from the inside no matter what I did.

Really surprised to hear @Rasiel saying it is very rare. Maybe I'm just bad luck. Lol. Most of the affected coins I have came from group lots and were not expensive coins (costing $200 or more). Maybe there's a sorting process by dealers where coins with suspected bronze disease find their way into group lots?

The sesquicarbonate treatment can remove some patinas but it is pretty effective after a month of soaking with frequent changes. It seems like some bronzes have chlorides internal to them which are extremely difficult to get rid of. 

I always bake my suspicious bronze coins for 2 hours at 200° f after treatment and try to store them in airtight containers with desiccant packages. 

There's a lot of misinformation about how to treat bronze disease, including recommending using toxic and dangerous chemicals. If you live in an area where the humidity is typically below 40%, you may never have a problem. If you live somewhere that typically has higher humidity, you may have a lot of problems.

John

I have seen how relative humidity seems to get the bronze disease process going. Three or four years ago I started collecting ancient, Early American Coppers, and (bronze) Large Canadian Cents. For about a year I just kept them stored in a room. Where I live, the humidity can get in the 60s, especially in the summer, and after a year I noticed several ancient bronzes with new green spots as well as several Early American Cents and Large Canadian Cents that showed similar corrosion. I treated these with Verdicare and had good results, then (following the advice of a Coin World article) created a "microclimate" for the coins, using a 3-gallon Rubbermaid container with appropriate absorbing material from the Wizard store (but available in many other places). I also added a hygrometer so I can watch the humidity as it rises and refresh the absorbing material every few months; this has worked out well. It is noted that sometimes the Verdicare changes the toning of he coin a bit.

I have learned a lot by reading everyone's responses, as different approaches seem to be effective according to one's individual circumstances. I think I have come from an outlook of not worrying enough, to be rather scrupulous with the microclimate, but now I take more risks and take the coins out and look at them a lot more and am not as concerned as in the past since I I seem to have a good general plan in place.

By the way, this issue is discussed among those who collect Early American Cents, and has been since collecting these became popular decades ago. There seems to be a consensus that storing them in air where there is moisture is to be avoided.

[KenDorney]

18 hours ago, rasiel said:

After having handled literally hundreds of thousands of ancient bronzes I can confidently say this is something that only happens with extreme rarity. When it does happen it progresses rapidly and ruins the coin in a jiffy. You can see the damage grow from one day to the next. And it's a very obviously wrong type of green, not something that leaves any doubt on whether it is or isn't. This photo is one of those rare ones I caught. Note that the green stuff isn't merely adhering to the surface but actively pitting.

Best answer here!  We see entirely too much talk about bronze disease.  It is usually obsessed over by new collectors who just need a little time and experience.  But there is so much info available already we dont need any more talk about it.  As a dealer ive also handled countless numbers of coins for what, over 40 years now and have only had a handful with the problem.  It is crazy rare when considering the total numbers of coins out there.

[ela126]

2 hours ago, KenDorney said:

Best answer here!  We see entirely too much talk about bronze disease.  It is usually obsessed over by new collectors who just need a little time and experience.  But there is so much info available already we dont need any more talk about it.  As a dealer ive also handled countless numbers of coins for what, over 40 years now and have only had a handful with the problem.  It is crazy rare when considering the total numbers of coins out there.

As you know, to a new collector, anything unslabbed is fake, and anything greenish is BD.

i think there is a perception of BD being some hungry virus leaping at the chance to instantly ruin a collection. Maybe this is a case in areas with no client control and high ambient humidity, but in climate controlled settings, i havent ever seen seemingly active BD progress much, and it's easily remedied and removed.