Author Topic: Bronze Disease  (Read 27749 times)

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Offline bruce61813

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Bronze Disease
« on: March 30, 2007, 08:26:05 PM »
  This is a problem with almost any Bronze item, not just coins. I have worked on coins, statues and even cybals for drum sets that have for various reasons been attacked.  It is the formation of Tinchloride mixed with copper oxide that gives it the pale coloring. If you are not sure about what it looks like I have attached a set of pictures at different magnifications.

  There are many ways to treat it, but it is not something that should be put off. If it is detected and treated early, thare may be no visable damage to the coin or object. but the longer it is left, the worse the damage, and that is not reversable. Here is an early article that I wrote on the subject. http://kevinscoins.ancients.info/BD/Bronze%20Disease.html. The simplist method of treatment is a simple mechanical cleaning, followed by a soak in distilled water with a mix of bi-carbonate of soda and sodium carbonate. This may take awhile but does work.

Offline Figleaf

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Re: Bronze Disease
« Reply #1 on: March 31, 2007, 01:18:13 AM »
Thanks for that contribution and link, Bruce. Is bronze rot similar to zinc pest? How would you treat it?

Peter
An unidentified coin is a piece of metal. An identified coin is a piece of history.

Offline bruce61813

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Re: Bronze Disease
« Reply #2 on: March 31, 2007, 04:29:05 AM »
Peter, I am not sure if it is the same. But it probably is, Zinc is a very reactive metal, and easily attacked by acids. Normal table salt, NaCl breaks down with water : Na+ Cl- + H20 = NaOh + HCl . the Hcl is hydrochloric acid and it attacks the Tin in bronze, and would attack zinc. Several years ago i developed a combination of the two sodas and some other chemicals that does work on Bronze disease, and have been selling  it in the coin world for 5 or 6 years now.  But I suspect the the same treatment described in my paper would work.
If you have a place to post the paper, I would be glad to update it and send it to you.

bruce

Offline Figleaf

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Re: Bronze Disease
« Reply #3 on: March 31, 2007, 11:12:59 AM »
We'd be delighted to post the paper! I have sent you a PM.

Peter
An unidentified coin is a piece of metal. An identified coin is a piece of history.

Offline bruce61813

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Re: Bronze Disease
« Reply #4 on: April 01, 2007, 07:15:34 PM »
Bronze Disease
Bronze Disease [BD] is to bronze metals, what rust is to iron based metals. The matrix of copper and tin that forms
 bronze is attacked by hydrochloric acid {HCl} to form tin-chloride and copper.
?The first step in the electrochemical corrosion of copper and copper alloys is the production of cuprous ions.
 These, in turn, combine with the chloride in the sea water to form cuprous chloride as a major component of the
 corrosion layer:
Cu -e >> Cu+
Cu+ + Cl- >> CuCl
Cuprous chlorides are very unstable mineral compounds. When cupreous objects that contain cuprous chlorides
 are recovered and exposed to air, they inevitably continue to corrode chemically by a process in which cuprous chlorides
 in the presence of moisture and oxygen are hydrolyzed to form hydrochloric acid and basic cupric chloride
 (Oddy and Hughes 1970:188):
4CuCl + 4H2O + O2 >> CuCl2 0 3Cu(OH)2 + 2HCl
The hydrochloric acid in turn attacks the uncorroded metal to form more cuprous chloride:
2Cu + 2HCl >> 2CuCl + H2
The reactions continue until no metal remains. This chemical corrosion process is commonly referred to as 
'bronze disease.' Any conservation of chloride-contaminated cupreous objects requires that the chemical action
of the chlorides be inhibited either by removing the cuprous chlorides or converting them to harmless cuprous
oxide. If the chemical action of the chlorides is not inhibited, cupreous objects will self-destruct over time." 1.
   Referring to the equations and comments in reference (1 ) above, BD is "contagious" through the green
cuprous  chlorides and care should be taken to wash away as much as possible. The ?fuzzy green? is easily
dislodged and if it can get into crevasses of other bronze coins, it will begin the cycle as moisture is
absorbed.

Now that you have been hit with the technical details, what are you really looking for?Look at this more
advanced case (below). The reddish-brown is copper that has been freed from the bronze matrix, and will
produce the "scarring" that is characteristic of BD.

What to Do
1.With running water and a  nylon brush, scrub the entire surface free of "green fuzz", allow to dry.
2.Use a magnifying light and a sharp needle to remove and open any obvious green spots still visible. With care
these will not be obvious later.
3.Pre-pare a bath of 5 parts baking soda [sodium bi-carbonate] to 8 parts washing soda [sodium carbonate].
You may go by weight or simple dry measurement, i.e. tablespoons full. Store the mix in an air-tight container.
[note: There is a commercially prepared version, if you don't want to make your own, contact me,]
4.Use de-mineralized or de-chlorinated water for better results.
5.Mix 2 tablespoon of the soda mix to three cups of water; add coins and heat the mix to boiling, reduce heat
for a minimum of 5 minutes. Set aside and soaking to continue for an extended period of time. This should be at
least 24 to 36 hours, for thick coins like Sestercious allow at least 96 hours. After the initial soak, rinse with clean
 water and give the coin(s) a light scrubbing.
6.Repeat step 5, twice more. For the repeat, the water need not be boiled, although warming to at least
120 degrees F  or about 55 degrees C, does help dissolution of the embedded salt.
7.After the last soak and scrub, dry the coins, and soak in 100% Isopropyl alcohol, for about 20 minutes.
This will help draw  out more water from the coin fabric. Dry thoroughly, and seal with a paste wax, well rubbed
 into the coin.
8.It is recommended that all bronze coins be checked periodically, as I have found "clean" coins suddenly break
out 2 years after purchase.
While this procedure should not effect a true green patina. It will remove any artificial coloring or
re-patination. Some artificial colorants are wax based, and will come off coins being cleaned.
Reference: For further reading - the following is where some of the information used in this article was derived, see the
footnote  1. http://nautarch.tamu.edu/class/anth605/File12.htm
Bruce Nesset 
« Last Edit: April 01, 2007, 07:44:38 PM by bruce61813 »

Offline Figleaf

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Re: Bronze Disease
« Reply #5 on: April 01, 2007, 07:58:05 PM »
Where do you buy washing soda and baking soda?

Peter
An unidentified coin is a piece of metal. An identified coin is a piece of history.

Offline bruce61813

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Re: Bronze Disease
« Reply #6 on: April 02, 2007, 05:02:33 PM »
This is a little hard to answer, since we have Europe, the UK , USA and Canada to deal with, each being a little different on how things are sold and labeled.

Baking soda is sodium bi- carbonate and should be available at any grocers or where you can find baking supplies

Washing soda is sodium carbonate [or soda ash] , in the US it is generall available where they sell laudry washing supplies. some people have found it with swimming pool maintence supplies.

Both items are fairly inexpensive, but they tend to come in large boxes, and you only need small amounts, so you often have large boxes of the washing soda sitting around. The baking soda is generally available in smaller quantities. 

Bruce

Offline Rangnath

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Re: Bronze Disease
« Reply #7 on: October 17, 2007, 05:10:36 PM »
A month ago, I purchased some uncleaned Kushan copper coins.  At least, I think that they are copper. They are slightly green in color and now lie in a sealed bath of distilled water. 
How would you proceed now? The same as with bronze coins?
richie

Offline bruce61813

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Re: Bronze Disease
« Reply #8 on: November 05, 2007, 03:18:35 AM »
If you are just trying to clean them, than adding some of the two sodas to the distilled water will help a bit. It would help if
you could post a picture. Green is not really bad, it could just be copper oxide, and 5 parts bi-carbonate of soda plus 8 parts sodium carbonate will help. A little dish washing liquid help.

Bruce

Offline Rangnath

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Re: Bronze Disease
« Reply #9 on: November 06, 2007, 11:10:25 PM »
Hi Bruce,
Here's an example of one of the Kushan coins I recieved.  What's your verdict Doctor?
richie

Offline bruce61813

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Re: Bronze Disease
« Reply #10 on: November 07, 2007, 03:55:27 AM »
It may be a tossup. I would go with caution and soak then in the soda mix or get some Gringgotts #1. The soak would not change the green very much, unless it was BD, it it is copper carbonate, it does not generally effect that. The soda mix would do just as well for these.

Bruce

Offline Rangnath

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Re: Bronze Disease
« Reply #11 on: November 07, 2007, 05:56:59 AM »
Thanks Bruce.
How long a soak would you recommend?  Would a soft tooth brush be ok to use at some time during the soak?
richie

Offline bruce61813

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Re: Bronze Disease
« Reply #12 on: November 07, 2007, 03:01:25 PM »
I would soak for about 3 days, after the first day, or even 12 hours, I would use the soft brush. the spots that bother ne most are the ones that show as 'bright green'. Watch then, but after 3 days they should be okay. Even scrubbing with a stiff nyling brush should not hurt. After the coins dry , keep and eye on them, but winters are generally dry and it is the summer at you would see a problem.

Bruce

Offline Rangnath

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Re: Bronze Disease
« Reply #13 on: November 07, 2007, 04:38:07 PM »
Thanks Bruce. I'll try to get the products today. I'll let you know how it turns out.
richie

Offline bruce61813

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Re: Bronze Disease
« Reply #14 on: November 08, 2007, 03:04:53 AM »
Try one coin first, the soda solution will dissolve the CuCL that is formed by BD, real long soaks, many weeks long, will dissolve copper oxide to some extent. The experimental part is the scrubbing, sometins a denture tooth brush works better than a soft one.

Bruce