Bronze Disease?

Hi guys, it has been a long time since I have posted anything on this forum or even interacted with my ancient coins. I put the hobby aside a few years ago and have recently (during lockdown) been digging through my uncleaned ancients again looking to clean and identify them again. However, I am really concerned that bronze disease may have spread across some of them as they were kept in the same containers. Most of these aren't really worth much but some of them may have some nice detail underneath the crud allowing them to be identifiable. In the past these were left to soak in distilled water (a lot of them within the same container), some containers I had actually forgotten about and were left soaking for a long time; although I did eventually empty the water out and left them be in the containers.

I have photographed four coins as a sample although there are a few more that I am suspect of. I'm sorry the pictures aren't great, I haven't got a professional camera just my phone, but hopefully you can see what I'm talking about. I tried to get a shot of them under my crappy microscope too.

Top right I have no idea as of yet, top left looks to be a Thyateira in Lydia (identifiable by what looks like an Apollo Axe), Seleucid Greek bottom left, and some other Greek bottom right. As you can see, top right has a nasty green concretion, the others have what looks like areas of greenish patina or dirt (I am unsure if this is BD)?

If this is in fact bronze disease, what methods can I use at home to get rid of it or stop it from spreading/worsening?

Hope you guys can provide some insight. I expect I'll be making more posts in the coming days as I struggle to identify some of my old coins! Cheers

 

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Tablespoon of salt dissolved in vinegar keep your eye on it but dont leave it too long

 

First, determine whether or not any of these coins actually has bronze disease. Get each coin wet, then set each coin out on a dish and check them once a week. If bronze disease is present, you will see a green powder slowly accumulate on the surface that you can brush off easily with your hand--it will literally grow on your coin like a fungus at the spot of the bronze disease.

If, after about 4 weeks or so, you don't see any powder growing out of and building up on the surface of your coin, then you don't have to worry about bronze disease. If you do see powder accumulating, then notify us right away. Left untreated, bronze disease will destroy your coin, but it works slowly, and it's very easy to treat with just distilled (not tap) water.

Personally, I would never put a bronze coin in vinegar, salted or otherwise.

 

Thanks for the info, I will test the coins with this method. Do I get the coins wet with distilled water or does the water type not matter?

Also, I just found another coin which definitely has BD. It had a green powdery substance concentrated in one spot and came away very easily. Although I remember this coin was badly damaged in this spot, it looks like the BD has made it worse letting it sit all this time. I've attached a photo with before and after I scraped away the BD with a closeup up of the green powder.

Could you describe the process to get rid of the BD with distilled water? Luckily this isn't a valuable coin, but hopefully I can save it from getting worse.

 

When you get the coins wet, use distilled water (DW), since you'll be using it to cure your one coin of bronze disease (BD) anyway.

Buy a gallon of DW from your local grocery. Brush off as much BD as you can from the afflicted coin. Use a toothpick or brass bristle brush to scrape around the affected area. Place it in a cup for 1 or 2 days, then take it out and dry it off with a rag. Replace the old DW in the cup with fresh DW and repeat this process. Do this repeatedly for 2-3 weeks. Then dry the coin off and set it unsealed somewhere where you will see it often. Check it every day or so to make sure the BD does not return. If, after 1-2 months, you do not see any more BD, your coin is cured, and you can treat it like you would any other ancient coin. If it does come back then you would need to repeat this regimen.

I have treated many coins this way. About 10% of them had the BD return and required a second treatment. I've never had to treat a coin a third time.

 

Great, thanks for the help! Unfortunately, I can't buy proper distilled water anywhere where I live in New Zealand (at least not for a reasonable price), I have looked for a long time. The only place I can currently find is selling it at $50 for 5 litres, ridiculous. All of the other stuff I see at our grocery stores are labelled as distilled or ultra-distilled water but they are meant for drinking, I don't think it's the same. I can also get demineralised water from an automotive store but I know this is also different.

Will the water from a dehumidifier be just as 'distilled' as real distilled water? This is what I have used in the past for cleaning, but for getting rid of BD I don't know if it will be good enough. Thanks again.

 

I picked up mine from a local garage. Its used to top up battery cells in cars......fairly common.

 

https://www.repco.co.nz/en/oils-flu...-demineralised-water-1l-dewater001/p/A1291582

This is the kind of water we get at our local garage/automotive stores. I'm not sure it's the same? Maybe over here people call distilled water demineralised, although I know that technically speaking there is a difference between the two - they undergo differently purification processes and demineralised is supposed to contain more organic contaminants.

I have heard that the 'distilled' water from dehumidifiers is the same as the bought stuff, but who knows if this is true?

 

I don't think it matters if the distilled water is meant for drinking. Unless the word "distilled" has a slightly different meaning in New Zealand than in the US--which I know is possible; just ask someone from England about knickers--it should be fine.

What you want is water with absolutely no chlorine (which can trigger the BD that you are trying to remove). If it has also been demineralized, so much the better. That will make it even more effective.

 

I buy mine at Coles here in Australia it is usually near the laundrey products on the bottom shelves, I presume there is Coles in NZ.

 

Bronze disease appears as a light green powdery area on a bronze coin. From what I could see from the images, I didn't see any overt signs.

Soaking in distilled water, as already mentioned, over a period of several weeks will tell whether or not the coin is afflicted with this problem. You have some pretty encrusted coins, so some of that material will likely soften and fall off the coin during the soaking period. Distilled water will remove the green powder, but unfortunately it is not a cure. Bronze disease could very well show up again after this process, so the coin needs to be monitored.

For coins with recurring bronze disease, there is a more high risk treatment, and I don't recommend this method for high value coins. A couple of years ago I got a lot of Byzantine bronzes from auction. The coins have a nice desert patina, as is often the case with this type. Unfortunately a nice Justin II and Sophia follis had bronze disease on the edge, and also in the middle of the reverse.

I soaked the coin in distilled water and added a small amount of sodium sesquicarbonate. Almost immediately the desert patina dissolved, revealing an even dark brown patina on both side. I left the coin in the bath for several weeks.

Upon removing the coin the bronze disease areas appeared clear, but just a week or two later the disease returned, so clearly the corrosion process in the bronze was continuing. I noticed that the bronze disease was developing in areas where there was still some patina remaining.

I proceeded to the next step, and, as I said, this step should not be followed with rare, high value bronzes. Using a toothpick, I dipped one end into a jar of Naval Jelly. This is a powerful rust remover. I applied it only on the spots where the bronze disease was coming back. Effectively I was removing all surface deposits and going down to the bare metal. I left the Naval Jelly on the spots for around 10-15 minutes, then washed the coin with distilled water. I then put the coin back into a distilled water bath, leaving it there for a couple of weeks. Upon removing the coin I set out on a counter for monitoring. I'm still monitoring it. So far the bronze disease has not returned, although now I have a coin showing exposed metal on the edge and in the center of the reverse. These areas are slowly retoning. That process could be sped up with liver of sulfur, but I don't want to destabilize the surface any more than I already have. As a recovering "patient" this coin will require constant scrutiny.

 

What you are after in cleaning coins is water that is 100% (or really close) water with no dissolved material. This can be distilled water or deionized water. I have seen admonitions about drinking distilled water, but am not sure they are valid. I have seen distilled water with "electrolytes" added sold for drinking water, but feel this is as much marketing as any other thing. If the distilled water you see in your supermarket does not specify "added minerals" or some such stuff, it would be safe. The only other thing that I would add would be to thoroughly dry the coins you want to be free of Bronze Disease (Verdigris). I have an electric oven and the warm setting is sufficient, I have seen 185 degrees F. Happy cleaning.

 

I do not think that Verdigris is the same thing as (or a sign of) Bronze Disease. At least, the results of a couple of Google searches indicate that they are quite different.

 

Bronze Disease is chlorides of copper, whereas Verdigris may be chlorides, carbonates or acetates of copper. I think the main difference is if the coin has a green coloration that is powdery and spreading or is harder and not spreading.

 

That was my understanding -- that verdigris is hard rather than soft and powdery, and shouldn't endanger the coin by spreading.

 

Anything with less than normal mineral content will be better than nothing. I'd try the grocery store stuff. In some places, the water is naturally free of minerals and will work while other places have water from wells with enough dissolved limestone in the water to make it worthless for the purpose. Tap water usually has chlorine which is not a good thing to put on coins. Perhaps the $50 reagent grade stuff would be better but I consider that as overkill. If you are running a dehumidifier and have that 'free', it should work. Years ago, I set up a pan which allowed the dehumidifier water to run over the coins and overflow effectively changing the water constantly. Grocery store water is easier. The less material other than H2O in your water, the more room there will be for things on the coin to dissolve into. Considering most of the uncleaned coin we see will never be worth as much as the cost of a bottle of water, we need to be reasonable in compromising here.

 

Here is the coin ("the patient") that is being treated.

The obverse shows no sign of bronze disease. The reverse, center and the lower right edge was treated. There's a trace of the desert patina remaining on the obverse, left side.

It's been over 3 months since I last had it in distilled water. So far, so good.

Sorry about the image. I'm still trying to figure out how to use this digital cam-
era - too complicated for my simple brain!

Byzantine AE Follis, Justin II and Empress Sophia, Constantinople mint, year 3.
13.7 grams, 11h.

 

Better image?

 

Thanks for the replies. I've now found two coins that definitely seem to have BD and will treat them with distilled water from the grocery store, I found one that claims to have no fluoride, metals or chlorine which sounds like it should do the job.

 

Good luck with the treatment.