World of Coins

Collecting coins => Cleaning, conservation and storage => Topic started by: bruce61813 on March 30, 2007, 08:26:05 PM

Title: Bronze Disease
Post by: bruce61813 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 (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.
Title: Re: Bronze Disease
Post by: Figleaf 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
Title: Re: Bronze Disease
Post by: bruce61813 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
Title: Re: Bronze Disease
Post by: Figleaf on March 31, 2007, 11:12:59 AM
We'd be delighted to post the paper! I have sent you a PM.

Peter
Title: Re: Bronze Disease
Post by: bruce61813 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 (http://nautarch.tamu.edu/class/anth605/File12.htm)
Bruce Nesset 
Title: Re: Bronze Disease
Post by: Figleaf on April 01, 2007, 07:58:05 PM
Where do you buy washing soda and baking soda?

Peter
Title: Re: Bronze Disease
Post by: bruce61813 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
Title: Re: Bronze Disease
Post by: Rangnath 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
Title: Re: Bronze Disease
Post by: bruce61813 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
Title: Re: Bronze Disease
Post by: Rangnath 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
Title: Re: Bronze Disease
Post by: bruce61813 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
Title: Re: Bronze Disease
Post by: Rangnath 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
Title: Re: Bronze Disease
Post by: bruce61813 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
Title: Re: Bronze Disease
Post by: Rangnath 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
Title: Re: Bronze Disease
Post by: bruce61813 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
Title: Re: Bronze Disease update
Post by: bruce61813 on May 25, 2014, 10:02:12 PM
Update to some of my add information. Copper II is the real problem, and in truth, Bronze disease should be called Copper disease. Copper II comes in 2 basic forms. the Anhydrous form is dark brown and inactive. as it slowly absorbs atmospheric moisture, it turns the characteristic cyan color we have called Bronze Disease, http://www.amazingrust.com/Experiments/background_knowledge/CuCl2.html (http://www.amazingrust.com/Experiments/background_knowledge/CuCl2.html) shows its transformation from anhydrous to saturated. In the green form, it starts doing its damage.

Bruce
Title: Re: Bronze Disease
Post by: Figleaf on May 26, 2014, 12:59:36 AM
When it comes to bronze disease, I am like a car driver who knows nothing about explosion engines: I know what to do, but don't understand the mechanics. Your paper suggested to me that the problem is caused by HCl, so I wondered how the coin got in contact with that substance. However, further on, I got the impression that the paper was written for coins found in the sea. I can understand that at least. My grandfather, who was into repairing fishermen's ships, would insist on having the propellors sprayed clean of salts when a ship went into dry dock.

Yet, coins not found at sea also suffer from bronze disease. Detectorists tell me the problem is artificial fertiliser. AFAIK, chlorine is normally part of artificial fertiliser. That would extend my understanding to coins found on land. Now, how about coins that have been in a collection of a very long time? Would they get bronze disease from polluted air?

Also, if there is copper II, does that mean there is copper I? What's the difference?

What I am after is some expertise on which coins are at risk and how to prevent bronze disease...

Peter
Title: Re: Bronze Disease
Post by: bruce61813 on May 26, 2014, 02:29:45 PM
It is difficult to say with precision what coins are at risk. The general answer is that the coins that are found buried or have been in contact with the soil for a period of time. It is not HCl that is the direct cause, as copper does not easily react with the acid. Here is a bit from my latest paper, as yet in finished.

What Happens and To An Extent Why.
    Copper in moist air slowly acquires a dull green coating, called Verdigris, because its top layer has oxidizes with the air. Some architects use this material on rooftops for this interesting color. The simple chemistry is as follows:

The green material is a 1:1 mole mixture of Cu(OH)2 and CuCO3.
2 Cu(solid) + H2O + CO2 + O2 → Cu(OH)2 + CuCO3(s)
Malachite is (Cu2(OH)2CO3). Copper II can  be generated by treatment of the hydroxide, oxide, or copper(II) carbonate with hydrochloric acid. In many cases it is the simple formation of Hydrochloric acid from Sodium chloride [NaCl] and water [H2O].
NaCl + H2O → NaOH + HCl

2NaOH + 2HCl + CuCO3(s) = NaCO3  + CuCl2  + 2H2O

Why is it so hard to detect?
   Anhydrous Copper II Chloride may appear in color from a dark brown to the cyan green, depend on the amount of atmospheric moisture that is absorbed. If it was in a desert region with very low relative humidity and dry air, it may never be seen. In moist or very humid areas, it changes color rapidly and starts to work on the solid copper. See the picture I posted earlier.  The color change of the copper II does explain why Bronze Disease is so hard to detect.

Back to your original question. All very old coins, especially finds by metal detectors, even small silver coins, should be treated in a soda bath.  this should be done as soon as possible after their exposure to air. I don't mean radical attacks on the coins, but get the mud, clay and dirt off, and allow the coin to soak in the soda bath or a high pH bath for a day or two. This may not eliminate the problem, but will help minimize the damage.

Exposure of any copper based alloy to salt spray or environs that have common salt, I am referring to NaCl or basic table salt, in the air, may be at risk, but it is limited. Think about modern coins, they are just as exposed, but because of being rubbed and handled , they for less of the needed oxides. The oxides are part of the equation.

I hope this helps.

Bruce
Title: Re: Bronze Disease
Post by: Figleaf on May 26, 2014, 05:43:23 PM
OK let me see if I grasped that. How about this re-formulation:

Bronze disease is a common oxidation process, like rusting iron. However, where iron will rust from exposure to air alone, in the case of bronze, a catalyser is needed. The most common one is salt (think of sea water and coastal air), but artificial fertiliser will do the trick also. The catalyser will accommodate the process, but oxygen (and water?) is still necessary.

Another difference with iron rusting is that the process feeds on itself. It will continue until the whole coin is gone. As the process eats into the copper, leaving traces, it is important to act as quickly as possible. When in doubt, act.

The coins most at risk are those found in the sea or buried on land. Give them a hearty soda bath immediately. If you just bought a copper coin, keep an eye on it. Look for changes in appearance, in particular brown, green or blue-green spots that grow bigger. When that happens, treat it as described above in reply #4. Be thorough. If you miss something, you'll have to start again later.

Peter
Title: Re: Bronze Disease
Post by: bruce61813 on May 26, 2014, 10:17:45 PM
Bronze disease is not common oxidation, it is one step beyond. Also the formation of Copper II causes a lot of damage. It really begins etching the metal surface. I noted that a brief 5 minute contact between my lab grade Copper II and a stainless steel funnel, made a notable etch pattern into the metal of the funnel.

Common copper oxidation is known as verdigris, and is mild, giving copper a dark green colored cover and is somewhat protective. whereas Bronze Disease is cyan in color and is self renewing. In the presence of NaCl it forms CuCl and will really do damage.

Bronze coins are not too long lasting in salt water, that is true. But it is due more to the reaction of the copper with other metals in an electrolyte.

Bruce [aka bruce61813 ]
Title: Re: Bronze Disease
Post by: Figleaf on May 27, 2014, 12:23:57 AM
Thank you, Bruce!

Peter
Title: Re: Bronze Disease
Post by: Levantiner on May 27, 2014, 03:45:08 PM
Theres another technique you might want try  But on a space filler coin first. I use it on Silver coins that have developed Verdigris ( and only when I want to stop the problem getting worse)  due to teh copper in the alloy corroding. The ingredients  Hot water, Household soda, Aluminium foil and a glass bowl.   Water and about two heaped spoonfuls of the soda go into the glass bowl.   put a small sheet of aluminium foil in the water.  Take the coin you wish to get rid of the Verdigris   imerse it in the water soda solution and ensure that it is touching the aluminium foil.        A minute is about as long as it should take ( 10 seconds is usually ample)    Take the coin out and wasjh it with cold water.    What happens is the Aluminium ends up corroding  while the oxides and sulphates on the coin are reduced. When done with a lightly corroded silver coin...you end up with a surface that looks like it has copper plating where the corrosion was......so it is only good for  Space fillers....the good thing is it stops the rot dead in its tracks!! Nver use it on a toned silver coin.....in a blink the coin will be "untoned"
Title: Re: Bronze Disease
Post by: bruce61813 on May 27, 2014, 03:53:20 PM
That technique is a chemical form of electrolysis, and has been used for years. If it is just verdigris, a solution of distilled vinegar and water with a soft cotton cloth should dissolve it, without harming the silver.

bruce
Title: Re: Bronze Disease
Post by: Figleaf on May 27, 2014, 09:40:33 PM
Wouldn't the vinegar dissolve the patina also?

Peter
Title: Re: Bronze Disease
Post by: bruce61813 on May 28, 2014, 04:55:25 AM

On Silver, it is possible, but if the object is to get rid of verdigris,then it is worth it.  Silver will darken on its own rapidly, sunlight and open air will do it.


bruce
 
Title: Re: Bronze Disease
Post by: Pellinore on September 04, 2015, 08:01:58 PM
@Bruce, how would you comment on the Wikipedia article (https://en.wikipedia.org/wiki/Bronze_disease) about Bronze Disease?
-- Paul
Title: Re: Bronze Disease
Post by: bruce61813 on September 04, 2015, 10:38:45 PM
It is the the same as what I have written. Neither of us is the first by a long shot. The process was developed by one of the major museums back in the 1920 - 30's and has proven effective, but slow. The benzo they talk about is fine, but highly toxic and a known carcinogen, that is why I stick to the soda/soda mix. It is cheap and effective.

Bruce
Title: Re: Bronze Disease
Post by: bruce61813 on September 04, 2015, 10:44:02 PM
JAIC online       
Journal of the American Institute for Conservation 
JAIC 1994, Volume 33, Number 2, Article 6 (pp. 141 to 152)   
 
A PERSPECTIVE ON THE HISTORY OF THE CONSERVATION OF ARCHAEOLOGICAL COPPER ALLOYS IN THE UNITED STATES
TERRY DRAYMAN-WEISSER
 
This is the paper that discusses the use of sodium sesquicarbonate [ home made by using 5 parts sodium bi-carbonate to 8 parts sodium carbonate].

Bruce
Title: Re: Bronze Disease
Post by: Pellinore on September 04, 2015, 10:55:05 PM
Excellent, that's useful to know! Thanks.
-- Paul
Title: Re: Bronze Disease
Post by: Levantiner on September 05, 2015, 07:38:58 AM
You might want to check out a product called Verdicare... its, appernetly designed for coins, but I have had no experience with it my self  It may be a commercial form of sodium sesquicarbonate
Title: Re: Bronze Disease
Post by: Pellinore on September 28, 2015, 02:10:30 PM
What would happen if you would make the soda mix stronger, I mean putting more soda mix in less water? Would the process go faster?
-- Paul
Title: Re: Bronze Disease
Post by: THCoins on September 28, 2015, 05:25:24 PM
Just try on a coin you don't like.
(I did. You usually end up with a very ugly surface of rough (uitgebeten) copper)
Title: Re: Bronze Disease
Post by: bruce61813 on September 28, 2015, 05:38:34 PM
Beyond the recommended strength it does not speed things up. Heating the solution, I us an old coffee makers, as it keeps the solution at about 150 F. Considering the coin has has centuries to absorb the salt, it will take awhile to leach it out.  Changing the solution every three days, and scrubbing in between will speed things. Multiple coins can be done at the same time. I us an open mesh pad on the bottom of the carafe so the solution touches the maximum surface area.


Bruce
Title: Re: Bronze Disease
Post by: Pellinore on July 12, 2016, 12:30:06 PM
Multiple coins can be done at the same time. I us an open mesh pad on the bottom of the carafe so the solution touches the maximum surface area.


So if you put two coins in one bottle (I'm using old plastic medicine bottles) with the sodium solution, they don't "contaminate" each other? I thought BD was contagious. How does the contamination work?
-- Paul
Title: Re: Bronze Disease
Post by: bruce61813 on July 12, 2016, 02:38:16 PM
n the dry powder form, BD can be passed from coin to coi, or holder they were in.  In a liquid solution it is neutralized and won't spread.  However the solution should be change,a couple time in the first 48 hours. The chemical reactions are relatively fast at first but taper off as time passes. By keeping the solution "fresh" you get the maximum reaction. Also, giving the coins a scrub every 12 hours or so and putting them in a clean solution will improve BD removal.

Bruce
Title: Re: Bronze Disease
Post by: Pellinore on January 23, 2017, 10:45:20 AM
A little bit more on the contamination process. What one's naturally afraid of, is that BD spreads from coin to coin in one's coin holders. Is that possible, or does it only contaminate if coins are touching each other?

In these drawers, I'm keeping my coins. I noticed that the little Persian bronzes I like are a bit BD-prone. Is there a danger in keeping them together, but in separate boxes like my system?

-- Paul


 
Title: Re: Bronze Disease
Post by: bruce61813 on January 23, 2017, 12:51:02 PM
There are two factors to consider.  BD "transmits" in its powered form, the light blue-green fuzz that sometimes appears in the early stages. It is this powdered form that gets onto other surfaces and to other coins. Humidity is the other factor, if the BD is present the humidity can provide enough moisture to activate it.

Any coins that show signs of BD, especially if it seems to recur, should be isolated and soaked in the soda/soda mix. I would do it for a couple weeks. Remember that the salts have had centuries to embed themselves. After the coins have dried, I would coat them with wax, REN Wax or a high quality paste wax [used for furniture].  This has two advantages. the first is that it restricts the ability of atmospheric moisture to reach the coin. The second is that the coins may be handled and not leave finger prints. they should be re-waxed every  couple years.

Bruce
Title: Re: Bronze Disease
Post by: jkk on April 04, 2017, 02:42:47 PM
I went ahead and tried the method on an ancient coin of Magnentius. It was a perfect candidate: otherwise had a lot of detail, and was a coin I would wish to conserve if possible, but it look like a smurf had sprayed spittle on it. I didn't heat the water, so it took longer, but sure enough: the proportionate mix of baking soda and washing soda in distilled water blew all the aquamarine smurf spit off it in about a month.

The process did leave rough spots, but they are better than having the rest of the coin eaten alive. I changed the solution out once a week, when the water started to turn a bluish hue. No doubt I could improve on my execution of the method, but it definitely worked for me. Thanks, Bruce, for a clear explanation of the process and the chemistry behind it.
Title: Re: Bronze Disease
Post by: bruce61813 on April 04, 2017, 03:07:47 PM
You are welcome. the rough spots can't be helped, the BD does remove some of the coins flan, so the sooner the treatment the better.

Bruce
Title: Re: Bronze Disease
Post by: jkk on April 04, 2017, 03:33:59 PM
You are welcome. the rough spots can't be helped, the BD does remove some of the coins flan, so the sooner the treatment the better.

And would keep doing so. The Cu in the BD has only one possible source, absent cross-contamination, and it isn't the atmosphere. I waited for a coin that I cared enough about to desire to improve, because I figured that a throwaway coin would not motivate me sufficiently to get the best results. Kind of like how I advise spreadsheet newbies: don't start with a fake practice project. Start with a real one that you care about, so that you are motivated to work through the problems as they arise. But in the case of coins, definitely not an expensive or rare practice project...
Title: Re: Bronze Disease
Post by: bruce61813 on April 04, 2017, 07:00:38 PM
You can do coins in batches, just change out the solution more often during the first few weeks. I also recommend a light scrubbing with a nylon brush, one of the type sold for cleaning dentures works very well, between soaks. Do this between solution changes.

Bruce
Title: Re: Bronze Disease
Post by: Pellinore on October 09, 2017, 09:03:11 AM
Bruce, 5 tablespoons bicarbonate and 8 tablespoons sodium. Makes about 200 ml stuff. And 3 cups of distilled water - makes 750 ml fluid, together a bit less than 1 litre? That is the idea? An American cup being 240 ml. Just want to know if I have the quantities right.
-- Paul
Title: Re: Bronze Disease
Post by: bruce61813 on October 10, 2017, 03:10:01 PM
Paul, you have it correct. the actual volume of water is not critical. I have used more or less, you are changing the concentration. the numbers
I gave are optimal, but not critical. Four cups [American] are about 10% short of a liter.

Bruce
Title: Re: Bronze Disease
Post by: Pellinore on October 10, 2017, 11:32:52 PM
Great, thanks! So I did do it right all these years. Here are the plastic pots on my window sill, filled with old Romans, Elymaeans (particularly prone) and other Persian bronzes. When the sun shines the water temp can get to 50 Celsius in the afternoon. The deepest blue water (second from right) contains coins I have given up, Im afraid.
-- Paul

Title: Re: Bronze Disease
Post by: bruce61813 on October 11, 2017, 03:11:21 AM
change their soak solution every three or four days, and give them a scrub with a nylon brush.  It takes about 4 weeks of this to remove most embedded salts , and the BD goes away.






bruce
Title: Re: Bronze Disease
Post by: Pellinore on October 13, 2017, 01:24:01 PM
Well, here are pics of the coins that I have given up, an Elymais tetradrachm and a 12 nummi from Alexandria, purported to be minted in 617-629 during the Persian occupation. The pics made from the side show that both coins have split and inside a squall of BD is forming, too.
-- Paul

Title: Re: Bronze Disease
Post by: bruce61813 on October 15, 2017, 03:28:33 AM
I would not give up. Use the BD mix, in a heated solution, give it a scrub, at least every 72 hours.  change the solution after the scrub. The bright blue is safe, it is Azurite and related to Malachite. Both are stable, hard forms of copper oxide. The may be salts deeply embedded, I have seen this type of layering before. I had a coin split into 3 layers. None could come up with a definitive reason for it. Possibly the original plan had flaws.

Bruce