Removing green copper oxides with Electrolysis, chemicals, etc.

[jake jot]

I soaked the following school medallion in water with salt for 20 plus years in the attic and at that time I didn't know copper could corrode and make green oxides. I also didn't think about it much and just forgot about it. I brought it down just today.

I read just a while ago that hot salty vinegar can help remove the oxides. But how can I apply it to all the surfaces, will soaking it for 30 minutes be ok or will the cooper get removed as well?

Can one use electrolysis and does it work for cooper oxide? What chemical(s) could be or are used in green cooper oxide removal?

 

[Borek]

Verdigris is not an oxide, more like some mixture of basic carbonates.

I doubt acetic acid will work. First, it is too weak, second, it was used in the past to produce verdigris, so even if it will remove some of it, it will probably also promote further corrosion.

I would go for the hydrochloric acid. Not too concentrated though, definitely something below 5%. I strongly doubt 30 minutes would be OK, but the only way to check is to try experimentally.

 

[jake jot]

Verdigris is not an oxide, more like some mixture of basic carbonates.

I doubt acetic acid will work. First, it is too weak, second, it was used in the past to produce verdigris, so even if it will remove some of it, it will probably also promote further corrosion.

I would go for the hydrochloric acid. Not too concentrated though, definitely something below 5%. I strongly doubt 30 minutes would be OK, but the only way to check is to try experimentally.

It's one of a kind medallion that i can't get again. So I won't experiment. I can just let jewelry service center remove them. Unfortunately. Their experiences are only with gold and silver. No one use copper or brass in jewelry. Hence the reason I need to be familiar with all kinds of cleaning especially chemical is to make sure they won't ruin it. Or know what they are exactly doing. They may try their techniques in cleansing gold and silver to it and it may not be compatible.

So others, kindly give all kinds of ideas how to separate the Verdigris from the copper/brass with least or no damage to the latter. Thanks.

 

[Borek]

Experimental part refers to the time required - this is rather unpredictable and depends on many factors. Diluted hydrochloric acid is a safe bet - it won't touch the copper itself and it will definitely dissolve verdigris.

Note that the copper is already potted with the corrosion under the patina, even if you remove it the surface won't look as it looked before.

But if someone has any experience I will gladly learn something new.

 

[jake jot]

Will vinegar work? The Jewelry service center told me they only clean gold and silver, and will use same techniques on copper or will clean it by scrapping home style. They don't have experience on electrolysis. Will electrolysis work on copper and verdigris?

 

[Mayhem]

Will vinegar work? The Jewelry service center told me they only clean gold and silver, and will use same techniques on cooper or will clean it by scrapping home style. They don't have experience on electrolysis. Will electrolysis work on cooper and verdigris?

Vinegar definitely will not work. From Wikipedia: " Verdigris is the common name for a green pigment obtained through the application of acetic acid to copper plates[2]".

 

[Vanadium 50]

Will vinegar work?

I doubt acetic acid will work.

That is vinegar.

 

[hutchphd]

What does the jewelry store do for gold? Copper should be similar.
I think electrolysis is the only viable method for perhaps reducing some of the damage but I do not know whether it will work for this system. If it works it might do wonders. I have removed corrosion from soft steel with remarkable success.
People who dig up old coins probably know this stuff...

 

[Vanadium 50]

I find ketchup works well on copper and brass, but it's never this tarnished. (This is not crazy - ketchup is a mild acid and mild abrasive)

While I don't know enough to recommend anything on something irreplaceable, I'd be thinking ultrasonics before chemicals.

 

[Tom.G]

Try this site for tips:
https://www.askthebuilder.com/cleaning-brass-products/

There are products that are specifically for cleaning Silver and/or Brass objects.

The one I've had success with on both both Silver and Brass is Tarn-X, the ingredients are listed at:
https://clrbrands.com/Products/CLR-Household/Tarn-X-Tarnish-Remover

Another possibility is to soak it in milk. The Lactic acid is quite mild but effective for some things. (I once left some spilt milk on a plastic car bumber, figuring it would do no harm. After a few months, that spot had lost all its paint!)

Cheers,
Tom

p.s. Please keep us updated on what works... and what doesn't.

 

[Mayhem]

You might have luck simply melting it off. Seems like verdigris has a far lower melting point than copper, so even if you butcher it, you won't hurt the underlying metal. Then you may have luck cleaning any residue off with vinegar, as this works for light verdigris.

 

[Mark44]

@jake jot , we call this metal copper in English, not "cooper". The Late Latin word was cuprum, which is the reason that Cu is the atomic symbol.

 

[jake jot]

By the way. In the same container with water and salt and medallion i put some crystal as i was trying out piezoelectricity. Water and salt is a conductor. For 20 yrs it is soaked there. So how did the verdigris from the copper transfer to the crystal? I tried using soap and water and scrub yesterday but the green hue of the crystal can't be removed. Will soaking in vinegar remove it? I don't want to damage the surface as i want to try piezoelectrity now and it may need smooth crystal surfaces. Also I am 100% sure these were clear color before as i have others i sold already. Natural green crystal is expensive.

 

[TeethWhitener]

There are lots of green crystals. There are lots of crystals in general. I have no idea what kind of crystal you started out with. I imagine after 20 years, some of the crystal's cations might have leached out and been replaced by copper cations, giving it a greenish hue. This would mean that no amount of buffing or polishing will take out the green color--it's part of the crystal structure now (at least to a certain depth, depending on diffusion rate of cations in and out of the crystal). However, there's no way to answer your question without knowing what kind of crystal you started with.

Also, only crystals with certain kinds of structure are piezoelectric. Are you sure you have one of those?

 

[jake jot]

There are lots of green crystals. There are lots of crystals in general. I have no idea what kind of crystal you started out with. I imagine after 20 years, some of the crystal's cations might have leached out and been replaced by copper cations, giving it a greenish hue. This would mean that no amount of buffing or polishing will take out the green color--it's part of the crystal structure now (at least to a certain depth, depending on diffusion rate of cations in and out of the crystal). However, there's no way to answer your question without knowing what kind of crystal you started with.

It is just generic clear quarts crystal. I know there are pink and green crystals. But I am sure it is not these colors.
If crystals colors can be changed by replacing the cations. Are there commercial processes where this is done? Is your description about cations the same as presence of hydroxyl groups or molecular water in the crystalline structure?

Yesterday I scanned it with a Raman spectrometer. This was the reason I removed the medallion and crystals in the salt water in the first place. To scan the crystals and take picture of the medallion to ask what is the green stuff. This is the green tainted quarts Raman spectrum.

What bonding produces the peak near 500 cm-1? This is zoom of the same crystal Raman scanned.

Also, only crystals with certain kinds of structure are piezoelectric. Are you sure you have one of those?

20 years ago. I was young. And my testing with Piezoelectricity unfinished. I just read then about shoes having crystals where stepping on the floor can charge battery put in the shoes and cellphone (when battery charge is gone). Imagine you are lost in the forest and your cellphone has drained battery.

 

[TeethWhitener]

Are there commercial processes where this is done?

No idea. Maybe companies don’t want to wait 20 years for their product?
I don’t know if a cation exchange has occurred here (silicon oxide is pretty stable), but then again, not too many experiments are done on the time scale of this one.

What bonding produces the peak near 500 cm-1?

Dunno. Elemental silicon is at 521 cm-1 but I doubt that’s it. Maybe check a database. Raman usually has pretty high resolution.

20 years ago. I was young. And my testing with Piezoelectricity unfinished. I just read then about shoes having crystals where stepping on the floor can charge battery put in the shoes and cellphone (when battery charge is gone). Imagine you are lost in the forest and your cellphone has drained battery.

Quartz is piezoelectric. And folks have been working on this idea for a while in various forms. It kind of works.

 

[Tom.G]

Quartz is piezoelectric.

And that is why it is used in high stability oscillators, typically at radio frequencies.

Oscillation frequency is determined mostly by thickness, and the temperature coefficient of frequency stability depends on the angle of the crystal lattice in the thin slice that is used.

Here is a link that may be of passing interest, also links within it.
https://www.antiqueradios.com/forums/viewtopic.php?f=5&t=136838

Cheers,
Tom

 

[jake jot]

No idea. Maybe companies don’t want to wait 20 years for their product?
I don’t know if a cation exchange has occurred here (silicon oxide is pretty stable), but then again, not too many experiments are done on the time scale of this one.

I soaked the quartz in vinegar for 30 minutes. 50% of the green stuff got loose. So I tried cleaning the medallion with vinegar. 20% of the green stuff got loose. I couldn't remove the rest, but some parts of copper covered by the verdigris were visible again. This begs the question. Does verdigris forms on top of copper, or does it replace the copper itself?

I don't trust the jewelry cleaner to clean it because they may use very strong chemical that may melt the copper. What chemicals can melt the copper?

In case I'll use the suggested HCL to clean it. Can I just soak it in HCL for 15 minutes and the verdigris would melt automatically? Or should I brush it? I don't want to use any brush using HCL as I don't want any accidental contact with my skin. I may just tell the jewelry cleaner to use HCL but they may not have it. Does jewelry cleaner generally also clean gold and silver with HCL?

Dunno. Elemental silicon is at 521 cm-1 but I doubt that’s it. Maybe check a database. Raman usually has pretty high resolution.

I found here the Raman spectrum of quartz, which matched mine in cm-1. The strokes shift Raman peak is at 464 cm-1. Anyone can explain why it varies from the Elemental silicon at 521 cm-1?

In situ Raman imaging of high-temperature solid-state reactions in the CaSO 4 –SiO 2 system | SpringerLink

My spectrum:

 

[TeethWhitener]

Does verdigris forms on top of copper, or does it replace the copper itself?

Verdigris is a copper compound. It’s “on top” of whatever copper remains, but it is formed from the copper that was there to begin with. So removing the verdigris won’t give you back your medallion; it’ll give you the medallion minus whatever copper has reacted to form the verdigris.

I don't trust the jewelry cleaner to clean it because they may use very strong chemical that may melt the copper. What chemicals can melt the copper?

Chemicals don’t melt copper; heat does. Chemicals such as oxidizers can react with copper.

In case I'll use the suggested HCL to clean it. Can I just soak it in HCL for 15 minutes and the verdigris would melt automatically?

Nothing is melting. The verdigris might dissolve. But as mentioned before, your medallion is now partially verdigris. The copper has reacted to form a copper carbonate (most likely), which is what you’re calling verdigris. Getting rid of it will remove that part of the copper permanently.

Anyone can explain why it varies from the Elemental silicon at 521 cm-1?

Because it’s not elemental silicon. Different compounds have different Raman spectra.

 

[mjc123]

The strokes shift Raman peak is at 464 cm-1. Anyone can explain why it varies from the Elemental silicon at 521 cm-1?

Completely different bonding situation. Silicon contains Si-Si bonds; quartz contains Si-O bonds. To be a bit over-simplistic: Vibrational spectroscopy (IR and Raman) characterises bonds, not atoms. X-ray spectroscopy, on the other hand, would tell you what elements are present (it looks at the energies of core electrons).

 

[jake jot]

Can Muriatic acid (dilluted HCL see below) work? This is used in home but i never used one. So should i put the medallion at the bottom of sink and empty the muriatic acid container to it, or soak it with muriatic acid for 20 mins?

Im just nervous working with muriatic acid. Just mere pouring it on the sink can release fumes?

I read this:

"Muriatic acid, a less-pure variant of hydrochloric acid, is available in high concentrations for use in a host of home restoration and maintenance projects.

While this powerful chemical agent runs cheap—about $10 a gallon at home centers, hardware stores, and even on Amazon—it’s still very caustic stuff, capable of corroding everything from some plastics and metals to clothing and skin. In fact, working with it poses numerous health risks: Momentary skin exposure can cause severe burns, inhaling its fumes can burn lung and nose lining, and contact can also cause irreversible eye damage or blindness."

 

[Mayhem]

Can Muriatic acid (dilluted HCL see below) work? This is used in home but i never used one. So should i put the medallion at the bottom of sink and empty the muriatic acid container to it, or soak it with muriatic acid for 20 mins?

Im just nervous working with muriatic acid. Just mere pouring it on the sink can release fumes?

I read this:

"Muriatic acid, a less-pure variant of hydrochloric acid, is available in high concentrations for use in a host of home restoration and maintenance projects.

While this powerful chemical agent runs cheap—about $10 a gallon at home centers, hardware stores, and even on Amazon—it’s still very caustic stuff, capable of corroding everything from some plastics and metals to clothing and skin. In fact, working with it poses numerous health risks: Momentary skin exposure can cause severe burns, inhaling its fumes can burn lung and nose lining, and contact can also cause irreversible eye damage or blindness."

If you're worried, wear gloves, safety goggles and wear long sleeved clothes in case of any splashing. Do all of it outside and make sure to dispose of your gloves immediately if you spill on yourself and put on a new pair. Use a chemically resistant container. You will be fine.

 

[Borek]

And when diluting always pour the acid into water, never water into acid. It is more important in the case of concentrated sulfuric, but still a safer way of diluting than the alternative.

 

[marcusl]

Doesn’t HCl eat metal plumbing?

 

[Borek]

Doesn’t HCl eat metal plumbing?

Depends on the metal. Yes, it will easily dissolve iron/steel, no, it won't corrode copper.

 

[marcusl]

Won't it be hard on the kitchen sink fixture, garbage disposer and waste pipes, to say nothing of potential environmental downsides of flushing acid into the city sewer?

 

[Mayhem]

Won't it be hard on the kitchen sink fixture, garbage disposer and waste pipes, to say nothing of potential environmental downsides of flushing acid into the city sewer?

Not really. Hypochlorite based drain cleaners are common. If you are worried about acids damaging your pipes, neutralize or heavily dilute your solution before disposing of it.

 

[jake jot]

Depends on the metal. Yes, it will easily dissolve iron/steel, no, it won't corrode copper.

What if the medallion is composed of cooper/iron alloy? How to tell? I used magnets and it didn't stick. Are magnets supposed to work on cooper/iron/whatever alloy? The following is after using brushes, soap, vinegar scrub for 20 minutes.

Look at the copper strip besides it. When I got the medallion about 25 years ago. It didn't look like copper. After spending 5 years experimenting on it. I stored it for 20 years.

Just wondering. Can anyone make out what images are in the center? Have you seen anything like it? I want to know how rare it is or just sold in market elsewhere.

 

[Tom.G]

The image seems to be the Egyption Pyramids in the background, the Sphinx in the foreground, and a Palm tree on the right and top.

Just as a wild guess, I suspect it is a tourist trinket someone got an a visit to Egypt.

If you get creative with a Google search you may find more info.

Let us know what you find!

Cheers,
Tom

 

[jake jot]

The image seems to be the Egyption Pyramids in the background, the Sphinx in the foreground, and a Palm tree on the right and top.

Very good. You are the only one who see through the verdigris coating?

Bottom of it is the Nile River.

I bought it from someone who got it from Egypt. I don't know if this was mass produced in tourist shop or specially made limited edition. Can someone from Egypt please share if this item is common in shop. So I can just get another one if I want to use it again.

So can HCL destroy copper/iron alloy and can this stick to magnets?

Just as a wild guess, I suspect it is a tourist trinket someone got an a visit to Egypt.

If you get creative with a Google search you may find more info.

Let us know what you find!

Cheers,
Tom

 

[Merlin3189]

I haven't read all the comments - I stopped when Borek told you the sensible answer, dilute hydrochloric acid.
But seeing the continuing discussion, I presume you don't have that, so I thought I'd mention that I've had success cleaning copper and brass with citric acid solution. I have this in my kitchen, but if you don't, maybe fruit juices might work?

 

[jake jot]

I haven't read all the comments - I stopped when Borek told you the sensible answer, dilute hydrochloric acid.
But seeing the continuing discussion, I presume you don't have that, so I thought I'd mention that I've had success cleaning copper and brass with citric acid solution. I have this in my kitchen, but if you don't, maybe fruit juices might work?

When I read that it will easily dissolve iron/steel, even though it won't corrode copper. What if the medallion is composed of iron/copper alloy or something. It may not be pure copper. How many copper alloy are there?

No. I don't wear it my shirt. And it's not something you can get a ebay. But Egypt. So it's precious in a sense. If i don't do anything. I wonder if the verdigris would increase further. Is it like rusts where if not removed, it would accelerate and keep growing and replacing the metal?

 

[Matcon]

... I've had success cleaning copper and brass with citric acid solution. I have this in my kitchen, but if you don't, maybe fruit juices might work?

That mixture works especially well when you include sodium chloride. Apart from being a mild abrasive, copper forms a soluble complex ion with chlorine. Most versions I have seen are salt and vinegar, applied with a Q-tip

 

[jake jot]

That mixture works especially well when you include sodium chloride. Apart from being a mild abrasive, copper forms a soluble complex ion with chlorine. Most versions I have seen are salt and vinegar, applied with a Q-tip

I have cleaned it with citric acid or vinegar. That's before I saw this sentence " Verdigris is the common name for a green pigment obtained through the application of acetic acid to copper plates[2]". "

It's conflicting. Some suggest to use vinegar. Some said vinegar will promote verdigris corrosion.

I will only try HCL if it can be proven it's 100% copper and not alloy. How can I know?

Well. Once I removed the verdigris. What can I paint it with? I'll sell it.

How much is this being sold in Egypt?

Does Egypt have internet? Any members here from Egypt?

 

[Matcon]

There are a couple of alternative approaches to consider, that I may be able to expand upon later.

Just on principle, I would experiment on copper coupons before trying unfamiliar chemistry.

There are two detailed articles about making and characterising verdigris:
https://pubs.rsc.org/en/content/articlehtml/2017/dt/c7dt03288a
https://pubs.rsc.org/en/content/articlehtml/2018/dt/c8dt01758a

Judging by the crystal structure, I don't see any ions being sufficiently mobile for electrolysis to work at practical temperatures. There is also the possibility that copper from the cleaner parts is dissolved preferentially, making the damage worse.

I would consider heating the object to partially or completely decompose the compound. This could be done in a neutral or reducing atmosphere to avoid excessive oxidation, but a fair amount of decomposition already occurs at about 200°C. Speculating here, the decomposition products may lend themselves to chemical cleaning.

A more off-the-wall approach would be to treat the compound as a hydroxide ceramic and look at ways of breaking up the hydroxide structure. A low melting point salt bath might do the trick. My starting point would be a mixture of carboxylic acids and perhaps a metal carboxylate. Unfortunately, phase diagrams of organic chemicals is not the sort of information that I have at my fingertips