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

 

[Matcon]

...

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

...

Vinegar will promote verdigris corrosion if you leave it in place.

Wash the vinegar off when the item is clean and dip in a weak alkaline solution to make sure there's nothing left in the crevices

 

[jeffinbath]

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.

I assume that after so many years in the attic the water would have all evaporated and left the medallion encrusted with salt when you rediscovered it right? Anyway I think you should use about a 5% solution of sodium hydrogen sulfate (also known as sodium bisulfate) to remove the copper salt. This is a cheaply available powder available on the Internet with no fume problems. Even dilute hydrochloric acid can give off small amounts of corrosive fumes, but more to the point it might etch further into the copper metal in the presence of oxygen from the air and in the water and its slight tendency to form complex copper chloride ions. Even though you may have some sodium chloride ions still in the encrustation, you would be unlikely to have trouble like this by using sodium bisulfate solution which will only produce copper sulfate and not a potential mix of Cu1 and Cu2 chloride ions.

 

[shjacks45]

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.

I worked in a printing circuit board shop as qc chemist. For tarnished Silver and Copper the tarnishing can be reversed and importantly the surface features are preserved. From your picture, your Copper Medallion appears corroded to where the underlying features probably no longer exist. Copper resists dissolving in strong mineral acids but I'd avoid Chloride as that's how this mess got started. Ammonia stinks but will rapidly dissolve insoluble Copper salts, and after the salts it will go after the Copper. Note that blue is the Cupric or Copper +2 compound. Copper likes to share so Cu+2 from blue solution and a Copper from surface gives 2 of Cu+1 which are favored by halogens like Chloride. The medallion could be x-rayed to determine surface damage before treatment. If it wasn't so corroded you could wrap it in Aluminum foil and put it in a baking soda or vinegar solution. Unfortunately any Copper already detached from surface is reduced to Copper powder.
As your medallion corroded, the surface is not evenly eroded but along machining stresses and imputiries (I'm curious about the pattern of corrosion.)
I would use dilute sulfuric acid (battery acid), vinegar would work eventually but its only 5% and you have pounds of crud to dissolve or loosen. Crystal Vanish or pool acid is Sodiumbisulfate (meaning half sulfuric acid) which would work.

 

[jake jot]

Vinegar will promote verdigris corrosion if you leave it in place.

Wash the vinegar off when the item is clean and dip in a weak alkaline solution to make sure there's nothing left in the crevices

Where to get "weak alkaline solution". What item in home can serve as it Macgyver style?

 

[shjacks45]

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

All of the halides and pseudo halides promote corrosion of Copper by lowering its e.m.f. vs Hydrogen (acid) electrode. Corrosion of Chloride is an order of magnitude lower than Bromide, but he had the Copper in brine for 25 years. The blue/green stuff is not the Copper corrosion. It is the reaction of Copper corrosion with air.

 

[jake jot]

I assume that after so many years in the attic the water would have all evaporated and left the medallion encrusted with salt when you rediscovered it right? Anyway I think you should use about a 5% solution of sodium hydrogen sulfate (also known as sodium bisulfate) to remove the copper salt. This is a cheaply available powder available on the Internet with no fume problems. Even dilute hydrochloric acid can give off small amounts of corrosive fumes, but more to the point it might etch further into the copper metal in the presence of oxygen from the air and in the water and its slight tendency to form complex copper chloride ions. Even though you may have some sodium chloride ions still in the encrustation, you would be unlikely to have trouble like this by using sodium bisulfate solution which will only produce copper sulfate and not a potential mix of Cu1 and Cu2 chloride ions.

Actually I added water and a 3 spoonful of salt into the basin every year. Sometimes I caught it without water as it evaporated. So I added more water and salt. This was done for about 20 years. Before that I didn't soak it but used it for 5 years (only soaking it weekly for 30 minutes). This is the only way to fix something in its wave function.

Please tell me if copper has any alloy version. Because one thing make me avoiding using HCL is if it has iron part in the cooper. Could it stick to magnet if there is iron bits?

 

[jeffinbath]

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."

Actually concentrated hydrochloric acid ,unlike sulfuric acid, is not that devastating on unbroken skin. I once upset a beaker of warm fairly concentrated hydrochloric acid on my legs and it did not hurt a bit. But what did hurt was seeing one of my nylon socks turning into a navy blue slime which I had to scrape off with a knife! However the vapor is harmful and corrosive. I recommend using sodium hydrogen sulfate (known commonly as sodium bisulfate) which is cheaply available on the Internet as a white powder with no vapor problems. A 5% solution should do the trick for you. It will simply dissolve all that green material into copper sulfate solution. Furthermore it is not likely to etch further into the copper metal, whereas HCl may do with the help of O2 from the air and in the water.

 

[rbelli1]

Please tell me if copper has any alloy version.

Bronze and brass are common alloys of copper that are used for this type of object. Neither contain large percentages of iron.

Could it stick to magnet if there is iron bits?

If there are iron bits then yes. If the iron is alloyed then not necessarily. Some stainless steels will not be attracted to a magnet even though they are made of a significant portion of iron.

Maybe this could work?

This is the only way to fix something in its wave function.

?

BoB

 

[jake jot]

Bronze and brass are common alloys of copper that are used for this type of object. Neither contain large percentages of iron.
If there are iron bits then yes. If the iron is alloyed then not necessarily. Some stainless steels will not be attracted to a magnet even though they are made of a significant portion of iron.

Maybe this could work?

Do you know of any jewelry that has copper or brass in it? Because if I just leave it to the jewelry shop, the repair worker with experience in gold or silver or diamond would just do anything he can to remove it. And I don't want him to ruin it. What kinds of chemicals typical jewelry repair shop used to clean gold, silver, diamond and other precious stuff?

?

BoB

You know the quantum state is only a tool that we use to predict the probabilities of different results for measurements we might choose to make of the system. But it doesn't mean it is all there is to it. The more complete description has more degree of freedom related to our consciousness. To make long story short. Water and salt can format imprint on some object. Without salt, the imprint can't be fragmented. I don't know why. It is future science. Or just say I'm superstitious (to avoid debates and let's just discuss or focus how to clean the verdigris, lol).

 

[rbelli1]

Do you know of any jewelry that has copper or brass in it? Because if I just leave it to the jewelry shop, the repair worker with experience in gold or silver or diamond would just do anything he can to remove it. And I don't want him to ruin it. What kinds of chemicals typical jewelry repair shop used to clean gold, silver, diamond and other precious stuff?

Some jewelry does have copper in it. Many people wear copper bracelets for various reasons.

I don't know what jewelers use for cleaning. You can ask about their knowledge and abilities for your particular piece. Presumably you will not just throw the medallion on the counter at the shop and run.

let's just discuss or focus how to clean the verdigris

Agreed.

BoB

 

[Mayhem]

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.

View attachment 274562

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.

You're right - it might be a brass trinket.

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?

If you use hydrochloric acid, the reaction will be slow enough for you to control it. It will take a while to get through the verdigris layer, and if you're attentive, it will only eat through only the upper layer of the medallion (IF it is an alloy) and make it shinier. Dilute acids tend to be quite slow acting, and you won't get an uncontrolled reaction with something like HCl. But it's up to you.

 

[jake jot]

You're right - it might be a brass trinket.

If you use hydrochloric acid, the reaction will be slow enough for you to control it. It will take a while to get through the verdigris layer, and if you're attentive, it will only eat through only the upper layer of the medallion (IF it is an alloy) and make it shinier. Dilute acids tend to be quite slow acting, and you won't get an uncontrolled reaction with something like HCl. But it's up to you.

You seemed to suggest hydrochloric acid was not the same as HCL. You mentioned how hydrochloric acid has slow reaction but HCL can get uncontrolled reaction, but are they not the same? Was it a typo? Please clarify.

Because if HCL reaction would really be slow, and I planned to just soak it for 5 minutes or pour the HCL into the medallion in the bottom of the sink to avoid working with acid for length of time (I don't have full gear protection except for virus only). Then I will really just give it to the jewelry repair shop but first discussing what he will do with all the facts shared here. If it is dubious and risky repair, then I'll just wrap the medallion with layers of silk or synthetic fiber. These can shield it. What chemical should I put in the medallion so it won't further corrode if I'd put it back in the attic wrapped in synethic fibers for another decade or two?

 

[rbelli1]

What chemical should I put in the medallion so it won't further corrode if I'd put it back in the attic wrapped in synethic fibers for another decade or two?

Once it is completely clean and free of the corrosion products place it in a tightly sealed container with a dry desiccant packet. Silica gel would be my first choice.

BoB

 

[chemisttree]

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

Well, we know that acetic acid is molten at room temperature. Glacial acetic acid MP is ~16C.

 

[jake jot]

Once it is completely clean and free of the corrosion products place it in a tightly sealed container with a dry desiccant packet. Silica gel would be my first choice.

BoB

I live in condo so no open air to do any acid work because of fumes. And i can't visit jewelry shop because of covid..so i was asking about storing it with the green verdigris still on. What to put in the medallion to avoid more corrosion? Also can any existing corrosion cause more corrosion, or no relation? By the way. In iron. Do existing rusts promote more rusts if the iron is put in proper place without water or vapor. Is this same with corrosion in copper?