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Help! My Coins Have A Fungus!!
Treating Bronze Disease.

What is Bronze Disease?   Treating It   Preservation and Storage  

So you say your ancient bronzes have a fungus and you don't know what to do about it? .

******************* From: Charlie Karukstis Regarding treatment of coins with bronze disease, I'd like to suggest a process that should be accessible to just about everyone. It's in the middle in terms of effectiveness, length of treatment, and difficulty. Place the coins in a glass container and fill with a 5% solution of sodium sesquicarbonate. Let them soak for about fourteen days, replace the solution, and soak for another fourteen days. Then, place the coin in distilled (or deionized, it truly doesn't matter) water for about a week. Stabilize with Renaissance Wax or Incralac. OK, now the notes on this treatment: (1) Don't have sodium sesquicarbonate lying around? You can make it with equal molar amounts of sodium carbonate (Na2CO3 - also called soda ash) and sodium bicarbonate (NaHCO3 - yes, you know what that is). For example, a 5% solution would then be 10.6g of carbonate and 8.4g of bicarbonate in 100ml of water. (2) a 5% solution WILL REMOVE any "patina" on the coin! If there is an exceptionally aesthetic "patina" to be preserved, try a 1% or 2% solution. Be warned, though, that it will take three times as long, and has a higher risk of being ineffective. (3) I was quoted out of context in the recent Celator article regarding distilled/deionized water. Yes, it can remove chloride ions from bronze (the cause of the "bronze disease"), but in an excruciatingly long period of time. The rinse is meant to remove any sesquicarbonate and byproducts after treatment. (4) An optional step before dealing the coin is to repatinate it; we can start a separate thread/tirade about that one. Suffice to say, I don't like converting a coin back to basic bronze unless it's necessary to save the coin. (5) Incralac is a lacquer containing benzotriazole (a chelate which will inhibit corrosion). Benzotriazole is a carcinogen (there - you're warned), and Incralac is difficult to use properly (I airbrush a thinned solution - very tricky to get the proper surface). Renaissance Wax is a very decent microcrystalline wax that, applied properly, will act as an effective sealant. Obviously, if you don't get all the chloride ions out, you don't want to be doing this. (6) The container must not have air in it - air will break down the solution prematurely. (7) Multiple coins are OK unless one has an inordinate amount of chlorides present. My trick to separate them? I use those nylon thingies electricians use to strap wires together. Pull it around the coin and snip off the end - the coins won't touch each other (a bad thing). Plus, they're inert. I think this is a much better approach than any mechanical method, which probably won't remove all the chlorides, or heating the coin, which simply removes water necessary for the reactions to take place - which will reoccur shortly thereafter anyway (especially in Houston!). This process is not that difficult to do (honestly!), and is actually a very powerful treatment available to us mere mortals. ***************************** From: Robert Kokotailo The bronze disease question comes up from time to time, and about two years ago was handled in depth on Numism-l. What came out of the Numism-l discussions was what I believe to have been a fairly good discussion of the cause and solution to the problem (mostly because of David Hendin's postings). The current discussion of it on this list show that many of the same mis-conceptions about it are still around. Unfortuntatly, I did not save all of it and have to work from memory. There is a Numism-l archieve that you can consult to find the original postings. First it is important to understand that bronze disease is caused by chloride ions in the bronze, and no amount of heating or coating of surfaces will stop the problem for any length of time. The chlorides require moisture to to react with the copper so heating will, by driving out the moisture, temporarily stops the problem and coatings may stop it for a longer period, but it will return. Coating the coin with anything will just lock in the chlorides, and probably make the problem worse in the long term. There is no need to keep coins apart (other then from direct contact), as the chlorides do not jump from one coin to another. This practice was started some time ago because it was once thought that bronze disease was a bacterial infection that could spread from coin to coin. This was proven to be incorrect long ago when coins were heated to very high temperatures (to kill all bacteria) with no long term results. Paul got to the heart of the matter when he wrote : >Regarding bronze disease; > >First soak the coin in deionized water (critical--not tap or other), changing >it every few days. > >Do so with at least a quart of water. > >Second, dry with hair drier. > >Third, watch to see if powder returns. > >If it does repeat. This works because the chlorides are water soluble and over a number of days or weeks of soaking in deionized water, they will eventually come out of the metal. Note that it is critical to use DEIONIZED WATER as other sources of water many introduce Chloride ions. Unfortunately, if your coins have been coated with anything (ie. wax, nail polish etc), it will have be removed for this to work. DO NOT WAX OR OTHERWISE COAT YOUR COINS AFTER TREATMENT. If the treatment was successful in removing the chlorides, the problem is gone (in which case the wax will not actually hurt), but if the treatment was not successful and some chloride ions remain, the problem may return and any coatings applied sill make additional treatments much more difficult and probably less effective. ****************** From: "Dave Welsh" ----- Original Message ----- From: To: Sent: Thursday, July 01, 1999 4:11 PM Subject: Re: [Moneta-L] Bronze Disease > From: AngShan@aol.com > > In a message dated 7/1/99 5:45:01 PM Central Daylight Time, > pauler10@ix.netcom.com writes: > > > Second, to add to the discussion, I am pretty sure the second coin does > > indeed have bronze disease. It didn't have this a few months ago. What do > I > > do? I know this has been discussed before but I didn't pay attention to it > > at the time. Help me save this coin! > > Well...I'll tell you my procedure for curing bronze disease; For coins in the beginning of bronze disease infection (ie; light infection); > 1) I put the coin in a jar of olive oil, let it soak for a week. This is completely useless. > 2) Scrub it very good with a medium bristle toothbrush under warm water. > 3) Wash off the remaining oil residue with a bath of tri-sodium phosphate. Ditto. > 4) Wash that off and bake them in the oven. 150 degrees for AR's, 250 degrees > for AE's. This will help. See below for why. > Deeply pitted bronze disease; > 1) Well, I use a rotary nail buffer with a small emory bit to drill out the > diseased pits. Some form of mechanixcal removal of the corrosion products is indeed necessary. > Then I perform the steps listed above for light infestation. Only one of which will be effective. > One thing that I DON'T do is coat them with nail polish or a wax! Absolutely right. Don't seal a coin with bronze disease until you're certain it is stabilized. Sealing isn't necessarily a bad idea, but not in this case! THE CAUSE OF BRONZE DISEASE: This is now understood to be a complex chemical process depending upon the presence of free or available chloride ions and moisture. The chloride ions combine with bronze constituents to create chlorides and other salts which then break down in the presence of moisture to liberate chloride ions and continue the corrosion. An aggressive case of bronze disease can ruin a coin in less than a month. ITS PREVENTION: Keep coins in a very dry environment. Bronze disease cannot propagate without humidity. Stabilize the surface of coins after cleaning and/or conservation, so as to remove all chloride ions. Do not store coins in any material that contains chlorine as a constituent -- PVC for example. ITS CURE: Bake the coin at 250 degrees F for enough time to thoroughly dry it out. Remove the choride ions by excavation and/or dissolution in deionized water. Dry the coin thoroughly and bake again to remove all moisture. Soak in deionized water again. Seal the coin or let it stabilize at normal ambient humidity. Another way to get rid of surface chloride ions is to immerse the coin in a 10% solution of sulfuric acid. This is a very fast process and requires skill, but if done properly will get rid of surface chloride ions without totally removing the patina. This is the only approach I know that works when the coins's whole patina is polluted by chloride ions (malignant patina). Have a DI water bath handy to rinse the acid off when the desired effect is reached. ***************************** From: Charlie Karukstis Just a few observations from our discussions of last night: (1) While de-ionized water is not distilled water, for our purposes they are interchangeable. What is critical here is the so-called "common ion effect". If you're looking to remove chloride ions from a coin, and the water you're using is already saturated with chloride ions, then you're not going to remove many ions (and theoretically could transfer more to the coin). Unless you're using Russian tap water, this is not likely to be a problem. Distilled water is perfectly fine for our needs (at least the distilled water available in the US is) (2) While boing water will speed up the process of chloride removal, unless you're prepared to boil the coin for a week this will not matter. Chloride removal using water only is a very lengthy process. If I can ever find some of Ian MacLeod's articles from Studies in Conservation from years back, I could post the actual time differences for the various processes being discussed (water, sesquicarbonate, dithionite, citric acid, etc). My point here is that while distilled/de-ionized water is a good thing, it is not a panacea for "bronze disease". (3) Whoever said that sulfuric acid won't remove "patina" (oxides, etc.) from a coin? Not in my neck of the woods, at least. Perhaps in very small concentrations, perhaps, but at that point I'm not sure why one would utilize it. A lot of the bulk coins coming from source countries that have been initially "cleaned" have been done using battery acid - suffice to say if you see what these coins looks like it's a substance to use carefully on bronze alloys. (4) Mechanical action on a coin is the preferred method for removal of encrustation (i.e. a scalpel under a microscope), but it's virtually impossible to successfully remove chloride ions this way. A chemical process is the only effective method I know of that will remove all traces of chloride ions. ************************************ From: Robehrlich@aol.com I have no experience in cleaning or preserving coins but pass on some information gleaned from a book I came across in a course on Greek bronze sculpture. An interesting article by Arthur Beale, from the conservation laboratory at the Fogg Museum of Harvard, is in the book, "The Fires of Hephaestos" by Carol Mattusch (Harvard University Art Museums, 1996). He describes the development of techniques for dealing with bronze sculptures as they evolved in last century. While some of the concerns are not relevant for coins, like the need for solder repairs, care to not change the metal composition or preservation of deliberate, ancient patination, others are relevant. The major initial corrosion product in bronze sculptures, particularly those that spent 2000 years deep in unxygented salt water, is cuprous chloride. This itself is not threatening. When it comes in contact with air above 46% relative humidity the copper oxidizes to the cupric form which is light green powder. The problem is compounded when the corrosion layer is overlaid by copper carbonates. He goes on to mention the techniques of prolonged extraction with distilled water followed by mechanical removal or superheated steam treatment. The use of sodium sesquicarbonate was discovered by an English chemist working in Egypt in the 30's. Both these techniques may take months. The treatment that is most accepted appears to be use of a complexing agent, benzotriazole, sometimes in conjunction with sodium carbonate. An unpublished method is use of silver nitrate as discussed in this group but it apparently has not been adopted. Two references in the journal Studies in Conservation (vol. 32, 25-40,1987m and vol 40, 110-119, 1993) use sodium dithionite (used in photography) and powdered zinc respectively. I have not looked at these references. The drawbacks to dithionite as well as sodium sesquicarbonate are changes in the color of the patination. Besides the problem of "bronze disease" associated with chlorides, the article touches on the dangers of sulfur and organic acids. Mahogany cases might not be a good idea as they could give off organic acids (i.e. tannic acid) unless the wood is thoroughly sealed. Any sealed container could be troublesome if the seals depend upon rubber gaskets which contain sulfur. The recommended storage is in powder coated steel cabinets. Coatings such as silicone have been found to be somewhat effective in preventing sulfur damage but less effective against bronze disease. Another reference that someone who has access to it might look at is "Ancient and Historic Metals: Conservation and Scientific Research" published by the Getty Conservation Institute in 1994. ***************************** From: Charlie Karukstis Rob has some excellent information in his post. To amplify some of his comments: (1) I currently am of the opinion that the sodium dithionite treatment is the most effective for (specifically) removing chloride compounds from bronze alloy coinage. I have used this process for nine years, and have had excellent results. Why did I not suggest it to the group in our earlier discussions? Because the trend of the thread was towards "accessible" treatments for "bronze disease", and unless you have the proper facilities for the dithionite process, it is something I cannot recommend to all numismatists. That is why I suggested the sesquicarbonate treatment (a fair balance between accessibility, effectiveness and length of treatment, as I mentioned in my post). (2) If you have access to the journal , there have been some excellent articles by Ian MacLeod (of the Western Australia Museum, I believe) concerning the relative merits of available treatments for chlorides in bronze alloys. The Getty book (Ancient and Historic Metals) is geared more towards metallurgical issues, and is less helpful for conservation issues currently under discussion. (3) As Rob mentioned, chlorides are not always found in isolation on coins. More generally, they will indeed be found in conjunction with carbonate compounds and even copper acetate (verdigris). It's not always easy to definitively identify the presence of chlorides. I will simply add from empirical experience that they are present (but usually stable, such as in the cuprous form) on more coins than we might wish. (4) Benzotriazole treatments are tricky to administer effectively. As it is also a carcinogen, this might not be the best approach for your rainy-day conservation sessions. Incralac (the lacquer containing benzotriazole that I mentioned earlier) is an excellent sealant with the benzotriazole acting as a chelate, but is not suited to removing chlorides. (5) Rob correctly notes that benzotriazole and sesquicarbonate treatments will alter the "patina" on a coin (actually. I'll go further than that - they will REMOVE the "patina" from a coin). Actually, any process short of distilled water will alter the complex layer of oxides, sulfides, carbonates, etc. on the surface of any bronze alloy coin - removing chlorides is a bit like chemotherapy: you can save the patient, but the patient will go through some changes. (6) I have always been somewhat suspicious of wood cabinets for storage of coins, precisely because of the possible emittance of various complex organic acids such as Rob mentioned. I really don't know much about them, and am still fascinated by them because of their elegance and utility. Would Paul, or Art Rubino (who sells these things) or anyone else care to discuss some of these issues with us? *********************************** -------------------------- From: Jim Gossett Rose Marie, Yes, there really is something called "bronze disease." Obviously, it's not a disease in the way one usually thinks of "disease." It's a catalytic process through which copper (a constituent of bronze) is turned into a fuzzy, green, soft mess. The coin is literally eaten away. It's catalytic, in that chloride ion, oxygen, and water initiate the process, but chloride (in the form of hydrochloric acid) is released again along the way, free to react with more of the coin's copper.... released again...and on and on. The fuzzy green stuff is a copper-hydroxide-chloride compound. It differs from the "good", hard green and blue-green coatings -- like malachite and azurite (hydroxy-carbonate compounds of copper). Bronze disease is treated by removing the fuzzy matter, and then treating to remove chlorides and water from the porous structure of the coin. Protective coatings are often applied thereafter to keep water from the surface. *************************************** From: "Charlie Karukstis" Rose Marie: The difference is that verdigris is copper acetate, while "bronze disease" is generally applied to cuprous chloride present in the flan of a coin. While copper acetate is in general fairly stable, cuprous chloride is anything but. It is quite unstable and active: in the presence of water and oxygen, cuprous chloride will convert to cupric chloride, while producing hydrochloric acid as a by-product; the HCL further attacks the flan, and the process continues. Cuprous chloride can be empirically identified (usually) by its powdery nature (because of its instability, it generally will not consolidate like copper acetate). While it tends to be of a lighter shade of green than copper acetate, don't use this as a hard and fast rule. There is not a topic in numismatic conservation that raises disputes like the causes and treatments of "bronze disease", and there is a lot of apocryphal information being disseminated (at least among amateurs). There is nothing, for example, of microbiologic process involved, and yet myths persist about treatment of the coin simply by heating the flan. While this will temporarily remove the water available for reaction, it is not a permanent solution. Likewise, mechanical removal of the chlorides cannot be successful owing to the usual porosity of ancient flans. The current best treatment for chloride removal, in my opinion, is the use of sodium dithionite, but as this is not a chemical for casual use, I generally recommend the use of sodium sesquicarbonate. If you can't obtain this directly, you can make it using sodium carbonate and sodium bicarbonate; we discussed this on this or another list a few months ago - email me for details. The usual admonishments about stabilization of a flan after treatment apply. ********************************** From: "S. Kazmi" Hi Rose Mary, Yes, the dreaded "bronze disease" is for real! It differs from the desirable "patina" as when gently scratched with a wooden toothpick it results in a powdery residue. One of the simplest methods to remove the bronze disease is to gently remove as much of the powdery stuff as possible, and then soak the coin in distilled water for at least three weeks (changing water every two days). Then "baking" the coin at 325 degrees for 10 minutes to remove all moisture and finally sealing it with a matte finish "hobby" lacquer or Renaissance wax. As this list seems the have a few "nuclear physicists" as members, I am sure some one can give a more detailed reply. **************************************** From: "Charlie Karukstis" One comment on the distilled water thread at the CNG site - while it will eventually remove most chlorides from the coin (through common ion exchange), it will take a very long time, and require quite a few changes of water. If the coin has active chlorides, the sodium sesquicarbonate process I mentioned a few months ago might be a better approach, and is not difficult. I agree with Ken on the importance of sealing a <> coin; I use either Renaissance Wax or Incralac, depending. One caveat to remember is that if there are, for example, active chloride ions remaining in the flan after sealing, the coin might very well continue to be attacked - it's important, therefore, to stabilize (through treatment and rinsing) a coin before sealing. Another risk is if an small area of the flan is not sealed, it could possibly function as an anode. One other thing - a dehydrator is just fine, but I almost always dry a coin using acetone. No effect on the surface (unless of course waxes, paint or the like are present) and much quicker. *************************************

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