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Alexander Chalkos Bronze Disease Solution

 
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Author Previous TopicReplies: 10 / Views: 272Next Topic  
New Member
Romania
12 Posts
 Posted 04/07/2021  04:19 am Show Profile   Bookmark this topic Add imparatul to your friends list Get a Link to this Message
Hello,

I have recently purchased this chalkos of Alexander that has what I presume is bronze disease. I would like to stop it from expanding if it's possible, so I'm asking for a solution to do this. Thank you very much!

Valued Member
Australia
341 Posts
 Posted 04/07/2021  06:23 am  Show Profile   Bookmark this reply Add echidna to your friends list Get a Link to this Reply
WD40
New Member
Romania
12 Posts
 Posted 04/07/2021  06:48 am  Show Profile   Bookmark this reply Add imparatul to your friends list Get a Link to this Reply
Won't WD40 damage the coin?
Valued Member
Australia
341 Posts
 Posted 04/07/2021  06:57 am  Show Profile   Bookmark this reply Add echidna to your friends list Get a Link to this Reply
No it will not damage it.
New Member
Romania
12 Posts
 Posted 04/07/2021  07:15 am  Show Profile   Bookmark this reply Add imparatul to your friends list Get a Link to this Reply
Do I soak it? For how long?
Valued Member
Australia
341 Posts
 Posted 04/07/2021  08:14 am  Show Profile   Bookmark this reply Add echidna to your friends list Get a Link to this Reply
Soak the coin fully in WD40.
Based on the images I'd say 30 minutes or so would do.
If that's not enough then do it again.
But experiment on one or two other coins first and you will get the idea.
Bedrock of the Community
Australia
18357 Posts
 Posted 04/07/2021  09:17 am  Show Profile   Bookmark this reply Add sel_69l to your friends list Get a Link to this Reply
Verdigris is a complex insoluble salt of copper hydroxycarbonate. The best way of passivating and removing it is to dissolve it. No severe mechanical tooling required.
The chemistry of choice used by museums for the conservation and display of copper and bronze objects is to use a solution of sodium sesquicarbonate, where the copper in the verdigris is replaced by soluble sodium in solution from the sodium sesquicarbonate. Insoluble copper carbonate precipitates out.

Sodium sesquicarbonate is difficult to buy, because it is semi unstable in air. However, is can be made by mixing the common and reasonably harmless household chemicals of baking soda and washing soda.

Google for instructions on how the mixed solution is prepared and used.

Some museums also preserve their treated coins with Renwax, which seals the surface of the coin, and prevents verdigris from starting again.
Mainly used for ancient bronze coins, where the natural patina can vary greatly in color and darkness.
Edited by sel_69l
04/07/2021 09:28 am
Valued Member
United States
387 Posts
 Posted 04/07/2021  09:34 am  Show Profile   Check Seeker55's eBay Listings Bookmark this reply Add Seeker55 to your friends list Get a Link to this Reply
Having used it successfully several times, I agree with the recommendation to use sodium sesquicarbonate, soaking the coin for a few days at room temperature

Formula for sodium sesquicarbonate solution:
10.6 g of sodium carbonate (washing soda) and 8.4 g of sodium bicarbonate (baking soda) dissolved in 100 ml of distilled water
New Member
Romania
12 Posts
 Posted 04/07/2021  10:07 am  Show Profile   Bookmark this reply Add imparatul to your friends list Get a Link to this Reply
Thank you very much for your answers!
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United States
842 Posts
 Posted 04/07/2021  1:54 pm  Show Profile   Check louisvillekyshop's eBay Listings Bookmark this reply Add louisvillekyshop to your friends list Get a Link to this Reply
Well anything you react with the Copper might be useful to form a more stable salt that is less of a problem. Brown.edu says the following about chemical composition:

--->"The actual chemical reaction is still not fully understood, though the chemistry of corrosion has been studied for some 150 years. However, the basic understanding of the process indicates that the presence of cuprous chloride in copper alloys reacts with water to create hydrochloric acid. The acid then eats away at the bronze, and in turn reacts with the copper. This second equation produces the visual manifestation of the disease: that dreaded green fuzz. Generally, the fuzz covers pockmarks caused by the hydrochloric acid."<---

+H2O ----> 2HCl + Cu2O
2HCl + 2Cu ----> 2CuCl + H2
A basic representation of the chemical process.

There is a great presentation below for this:

http://www.crescentcitycoinclub.org...0Disease.pdf

So can you react the copper to something less horrible to deal with? Something more stable? Well notice they mention the sodium sesquicarbonate quite extensively but they also mention some fish tank cleaning chemicals as an alternative. They can have thiosulfate so you might pull the chloride off and do this:

CuCl2 + Na2S2O3 ----> CuS2O3 + 2NaCl

Thus you have choices..... Probably end up turning the coin black with the fish cleaning chemicals if you are not careful. So maybe clean out the spots and then q-tip applications into pits with drying?

Citations:
https://www.brown.edu/Departments/J...st/4867.html
Edited by louisvillekyshop
04/07/2021 1:59 pm
New Member
Romania
12 Posts
 Posted 04/07/2021  2:46 pm  Show Profile   Bookmark this reply Add imparatul to your friends list Get a Link to this Reply
Thank you!
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