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I'm trying to decide what to do with this...


CPK

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Recently acquired this coin which looked as if it might have some - you guessed it - bronze disease going on. (Am I too paranoid about this??)¬†ūüôĄ

I thought, well, I can probably deal with it, I've done it before, so I didn't feel too apprehensive about it. The coin itself is beautiful, with a glossy dark patina and a great portrait of Tiberius.

Here are the auction house photos:

526D.jpg.84ee4f7f0912bd66f4f3f172b8a0c0eb.jpg

 

Upon receiving the coin I alternated scrubbing gently with a toothbrush and rubbing/picking at the stuff (under magnification) with a toothpick in distilled water. I was able to remove some of the bluish/green spots. I had several goes at the coin. Then I took my own picture - (the auction house photos didn't do the coin proper justice!)

tiberius_as_02.jpg.c2d0416f9838d80a78834bd08ce02db0.jpg

 

As you can see, the hard spots are gone but I'm still left with some faded color. I should stress that what spots that remain are very stubborn; I poked very hard at it with the toothpick.

So I have a few questions:

First, Is this BD in your opinion?

Second, If so - since BD needs moisture and access to air to be active - if I blow on the coin for a long time with a hot hair dryer to remove the moisture, and seal the coin's surface with Renaissance Wax, would this prevent further damage? From what I understand, Ren Wax provides a thin hard coating on the surface and ought to prevent moisture/air from reaching it. If this is so, shouldn't it essentially "cure" any BD still there by permanently halting the process? Or am I wrong on this? I have heard of a product called Verdicare which is said to be able to "cure" bronze disease in a similar way - by sealing the surface of the coin. @Roman Collector had a thread about it awhile back.

Third, If I absolutely MUST I can try soaking the coin like I did before. But I really don't want to damage the patina/appearance of this one by using sodium sesquicarbonate. Will just distilled water harm the appearance?

Fourth and finally, What would you do with the coin?

Thank you for any help or advice you can give!

 

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45 minutes ago, Spaniard said:

Are the green stains powdery?

 

Hard to say exactly - the spots are pretty small - but I think so. Like I said I was able to scrape some of it away, and the toothpick tip was discolored. 

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56 minutes ago, robinjojo said:

Beautiful coin!  I'd keep under observation for an extended time to see if the green spots return. 

I really like the coin's patina.

I second this.

 

Beautiful coin. Be sure to keep it under observation.

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2 hours ago, JayAg47 said:

I suspect there's also some tooling going on, especially around his nose on the obverse!

I don't know, I thought it looked more like it a flat strike. Like this coin: (Not mine, BTW)

Mark Antony, Patrae (?), Autumn 32-spring 31 BC. AR Denarius. Legionary type. Galley R/ LEG XIII, Aquila between two signa (vcoins.com)

pFr2Hy9K5QYjaJ856rdNPJ7cs3BW4n.jpg.7720c10d525156e42ed43357bdd24e8b.jpg

Edited by CPK
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1 hour ago, robinjojo said:

Beautiful coin!  I'd keep under observation for an extended time to see if the green spots return. 

I really like the coin's patina.

 

14 minutes ago, Furryfrog02 said:

I second this.

 

Beautiful coin. Be sure to keep it under observation.

Thanks! In the meantime would you recommend keeping the coin in "quarantine" just in case?

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Sure, I'd just put it in a separate place, and way from any other bronze or billon coins.  It looks as if almost all of the green deposits were removed, but if they reappear, try giving the coin an extended soak in distilled water, changing the water from time to time for a week or two.  Then, observe the coin for several weeks or month or two.  Eventually you should have neutralized the corrosive process.  

Good luck!

By the way, have you noticed that there is a shortage of distilled water?  I've heard that it is yet another supply chain problem.

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2 hours ago, robinjojo said:

 

By the way, have you noticed that there is a shortage of distilled water?  I've heard that it is yet another supply chain problem.

I can attest to this! From what I’ve been hearing a lot more people are doing neti pods, which require distilled water, so I imagine that has some impact. I have picked up the habit as well and it’s amazing 
 

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7 hours ago, robinjojo said:

you noticed that there is a shortage of distilled water?  I've heard that it is yet another supply chain problem.

Not at all: there are always plenty of gallon containers in both supermarkets I go to here in Upper Manhattan. I have sleep apnea, so I use distilled water in my CPAP machine. 

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From Wikipedia:

------------------------

Bronze disease is an irreversible and nearly inexorable corrosion process that occurs when chlorides come into contact with bronze or other copper-bearing alloys.[1] It can occur as both a dark green coating, or as a much lighter whitish fuzzy or furry green coating.[1]

Initially, copper is oxidized to the cuprous ion:[4]¬†(1) Cu ‚Üí Cu+¬†+ e‚ąí

The cuprous ion reacts with the chloride ion to form the insoluble white colored salt¬†cuprous chloride: (2) Cu+¬†+ Cl‚ąí¬†‚Üí CuCl

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

The remaining copper is oxidised by air to the cuprous ion: (4) Cu ‚Üí Cu+¬†+ e‚ąí

The cuprous ion reacts with the chloride ion in the hydrochloric acid to form the insoluble white colored salt¬†cuprous chloride: (5) Cu+¬†+ Cl‚ąí¬†‚Üí CuCl

The reaction then repeats from equation (3). It is the presence of two different white and green salts that lead to the fuzzy green appearance.[4]

Initial treatment can involve placing the object in a desiccating environment.[4] Deprived of water, the reaction cannot continue. However, re-exposure of the object to even atmospheric water can restart the process.

-------------------------

I.e., bronze disease is an almost self-perpetuating chemical reaction that will continue unless the green cupric chloride is completely removed from the coin (thus eliminating the chlorine atom that enables the reaction) OR the coin is kept in an environment completely free of contact with water molecules.  You might attempt to do the latter by placing a desiccant alongside the coin in storage, but inevitably some water molecules will find their way to the remnants of the green cupric chloride and continue the disease process.  Distilled water is irrelevant in this reaction.

This means that the ONLY way to ensure that the bronze disease stops is by eliminating 100% of the green cupric chloride.  For more information on ways to do this, you should refer to the Wikipedia article: https://en.wikipedia.org/wiki/Bronze_disease

 

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19 hours ago, CPK said:

First, Is this BD in your opinion?

In my limited experience, yes, but it looks limited and mostly on the surface. If the green stuff comes off with a gentle picking, and is 'powdery', it's the chemical reaction called BD. In your second photo, the green colour is still present. Is it under the patina, as if it goes through it to the surface? And can you still pick it off? 

19 hours ago, CPK said:

seal the coin's surface with Renaissance Wax, would this prevent further damage?

If your coin has BD, I advice not to use RW, unless you are 100% sure the BD is gone. Mostly it takes a lot of time (months, even a year) before you know that for sure. I've read about 'drying' the coin, but like @idesofmarch01 mentioned, as soon as water molecules hit the chloride molecules, the reaction will start again. The difficulty is that RW might actually encapsulate the molecules. 

19 hours ago, CPK said:

Will just distilled water harm the appearance?

In combination with scrubbing the coins surface with a toothbrush, it might slightly. 

19 hours ago, CPK said:

Fourth and finally, What would you do with the coin?

Clean it and keep it. The BD is not in the lettering, or on the portrait or relevant details on the reverse, so any damage does not disturb the essence of the coin. 

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12 hours ago, DonnaML said:

Not at all: there are always plenty of gallon containers in both supermarkets I go to here in Upper Manhattan. I have sleep apnea, so I use distilled water in my CPAP machine. 

Then it must be a San Francisco bay area problem.  The supermarkets are out of stock most of the time.  I was lucky to buy a gallon last week, probably should have bought two, but I really don't need distilled water as much as people who use cpap machines.  I have no idea what other water can be used to clean them.

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I actually wanted to start a thread about it, but I might as well add it to this thread if @CPK wont mind...

I'd like to share some photo's and experience with threating a nasty case of bronze disease. To start off this post, I'll post the original photo of the coin, I bought in 2015. At that time I was relatively new to the hobby, and never heard of bronze disease. Had I however, I would not have bought this coin (lesson 1; now if I'm interested in a coin but suspect a possible case of bronze disease, I always ask the seller if the green spots are active or not. If not, and in case I buy the coin, I always check it myself at home with a toothpick and keep it in DW for a few weeks). 

322122288_Caligula2015.jpg.bdb328031176baf0de81685980c22b36.jpg

As you can see, the obverse has the case of BD, with severe corrosion back of the head, and small green spots are emerging at the surface. Also notice the small green dot on the lip of the portrait. 

These photos were taken in 2018, three years later. As you can see, the green spots had worsened, and, difficult to see on this photo, green spots also had emerged at 8 o' clock on the obverse, on the side of the coin, next to the 'C A E S', where on the photo of the seller in 2015, corrosion can be seen. 

1791586932_09CaligulaAs.jpg.be18f68dc91eeb58903a4bdb9e547bf1.jpg

About, I think three years ago, maybe a bit more or a bit less, someone at cointalk informed me of BD, when I posted these photo's of the coin. I delved into the matter, and then started on a long process of cleaning the coin as good as I could. 

I first started with a gentle scrub, a wooden toothpick and DW. Unfortunately, the BD was deep in the coin, and when I picked the green corrosion on the surface, I could see with the magnifier new green stuff below it, deeper into the surface of the coin. I then started to use the more heavy equipment, cutting away the infected metal. I chose this method over e.g. electrochemical method, but both physical and electrochemical are possible. The result: 

6_1v.JPG.bc0d024067bb7396534fc7ee98ff567c.JPG

I was quite pleased with the result. The more important details were still present. The only real mistake I made, was that I slipped and a scratch appeared in front of the lip of the portrait. As you can also see, the darker patina was slightly removed from the higher areas of the portrait. Difficult to see on this photo, but this is also the case on the lettering. The reverse showed no sign of BD, so I left that alone. 

Under the magnifier however, I still could see small green spots, hardly noticable with the naked eye. Afraid this might still be BD, and/or might worsen, I next decided to use the chemical approach. Do not, during this process, verdicare was not available for a long time. First, again, long soaks in DW. I think in all this coin spent about a year in DW, which I refreshed on a two week basis. Next, I looked for a chemical to acquire, and decided to try 'Gringgott's Bronze Disease Killer'. I'm not sure what is in it, Im guessing sodium carbonate, but I'm glad it got through customs...

I firstly used a light mixture of the Killer with DW using the formula on the package; it resulted in a transparant liquid in which I first put on the coin with a cotton swap. The result:

Cal_2.jpg.db1d059f7062074064ed3f20f2dc024d.jpg

Next, I complete soaked the coin. First a few seconds, to see what would happen. Then a few minutes, then a few hours and ultimately 48 hours. I was unsure what the effect of the mixture was, as I could see no difference compared to the situation before applying the liquid. Under the magnifier, the green spots seemed unchanged. So I decided to step up the game, and used the formula mentioned on the website of the seller. Well, not quite a formula, the description is applying a 'paste', so I tried to create it, as good as I could (im not a chemist). The process:

cal_3.jpg.cbcad8940c9b907da250344ba24acd9c.jpg

I applied the paste directly to the infected areas. The reverse was untouched. I left it for about 48h, checking in between, after which it looked like this:

cal_4.jpg.7085fcddb2234ac6723b03cdc9c22290.jpg

As you can see, the formula turned green, and behind the head it seems to have disolved, but actually it turned into a more liquid form. I cleansed the coin with regular tap water, then gave it a scrub with a toothbrush and DW, and applied the formula again for 48 h. After that, the coin looked like this (you can clearly see the scratch now, near the lip): 

cal_7.jpg.23783d1fcbee5c10167a10ee4516b94b.jpg

I'm quite pleased with the result. Obviously, most of the patina is gone, but the BD seems to have disappeared. There are no spots left. What is left, is the copper and deep corrosion, due to the physical cleaning. I hope my efforts will be enough. 

I chose not to bake the coin in the oven, or use another method to dry the coin. I simply dried it with a clean baby cloth, and placed it in our cabinet (not next to my other coins). Now starts the long wait, I think a year or so, maybe even longer. I will regularly inspect the coin, to see if anything happens. After this period, I will apply a chemical I purchased at the same seller, to repatinate the coin. The reverse is still untouched, although the higher areas have been infected by the chemical, touching, etc, and the patina is also gone on those areas. But the damage is minimal. [edit: I will only apply the patina chemical when I'm 100% sure the BD is gone, otherwise I'm affraid I will capture the BD under the patina). 

So, some more lessons:
- go easy with the physical cleaning and use the best tools available to limit the possibility to damage the coin
- take the chemical cleaning slow, use steps and see the effects before taking the next step
- only do the cleaning yourself if the coin is worth it; I decided to do it myself, because I found it interesting and I'm at peace with my efforts vis-a-vis the price of the coin when I bought it. It this were a $ 1000 + dollar rare Nero sestertius I would have 1) never bought it, or 2) return the coin for a refund, or 3) had it cleaned professionaly.
- accept that whatever method you use, you will hurt the coin. So if you don't want to do that, see 1) and 2) above. 
- take your time. Its a slow, very slow process....! 

Thanks for reading! And will post the results of the repatinating process in a year or two ūüėČ

 

Edited by Limes
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1 hour ago, robinjojo said:

Then it must be a San Francisco bay area problem.  The supermarkets are out of stock most of the time.  I was lucky to buy a gallon last week, probably should have bought two, but I really don't need distilled water as much as people who use cpap machines.  I have no idea what other water can be used to clean them.

You can certainly order distilled water online via Amazon or some other platform. I sometimes buy boxes with multiple gallon containers online, so I don't have to go buy a new one every time I run out. Plus, those individual gallon containers can start feeling pretty heavy walking home from the supermarket!

Edited by DonnaML
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