Removing green copper oxides with Electrolysis, chemicals, etc.

[Matcon]

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

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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?

 

[chemisttree]

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?

Corrosion is an oxidative process. You could try to exclude oxygen but if you are storing it for decades, that won’t work without a $eriou$ effort. There are anti corrosion chemicals like benzotriazole and triethanolamine, but those work best on pristine metal surfaces. Best bet is some kind of lacquer that can be removed at a later time, in my opinion.

Also can any existing corrosion cause more corrosion, or no relation?

.
Yes, by a process known in corrosion science as Differential Aeration Corrosion.

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?

Yes.

 

[shjacks45]

Or you could just pressure wash the thing. No chemicals. Wood and metal resist high water pressure, so the underlying copper should be OK.
Your picture showed bluish and whitish crust, the blue Copper and white could be Lead or Zinc. If it had Iron it would be rusty orange.

 

[jake jot]

Or you could just pressure wash the thing. No chemicals. Wood and metal resist high water pressure, so the underlying copper should be OK.
Your picture showed bluish and whitish crust, the blue Copper and white could be Lead or Zinc. If it had Iron it would be rusty orange.

This is back of it. Bluish and whitist crust? The front has green only, maybe your monitor color balance setting? And you mean it contains lead or zinc? some kind of lead or zinc alloy? Meantime I put it in a plastic container and put back in attic. I'll give it to jewelry repair shop when Covid is over and I'm confident he won't ruin it (reviewing all your chemistry tips, thanks for them). I guess Covid will be over by April or June. I need to soak it in salt water for 30 mins once in 2 months (to clean the absorbed prana). I guess shaking in pure water afterwards can loose any salt and cleaning with dry clothe would be ok to avoid more corrosion, isn't it?

 

[chemisttree]

Brass - Copper/zinc alloy
Bronze - Copper/tin(sometimes arsenic) alloy

Yours is probably bronze.

 

[tech99]

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.

View attachment 274265

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?

Dilute Hydrochloric Acid of strength about 2 Molar will react with the copper salt but will not react with Copper. I also agree with another comment suggesting Citric Acid. Acetic Acid (Ethanoic Acid) is not recommended as the product is also green.
I have often used weak household acids to remove corrosion of copper cables, which requires just one minute in a dilute acid.

 

[Matcon]

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

There are quite a few so-called NAtural Deep Eutectic Solvents, or NADES, consisting partially or completely of carboxylic acids mentioned in the literature:
https://ifst.onlinelibrary.wiley.com/doi/abs/10.1111/ijfs.14013
https://www.sciencedirect.com/science/article/abs/pii/S0196890405001858?via=ihub
https://www.ias.ac.in/describe/article/jcsc/126/03/0881-0887

 

[James Demers]

You might consider sandblasting - but with walnut shell instead of sand. This is a commercially available abrasive, which breaks up brittle oxides but doesn't erode metal surfaces. Museum curators use it to take the accumulated patina off of outdoor bronze sculptures. A local auto body shop might be the best place to take it!
https://www.ceroglass.com/products/shotblasting-and-peening-media/walnut-shells

 

[James Demers]

It is almost certainly a tourist trinket - there are lots of little shops in Cairo that bang out this sort of thing from copper or brass. There's a famous bazaar, the Khan al-Khalili, which is quite popular with tourists, and where this was probably bought: https://en.wikipedia.org/wiki/Khan_el-Khalili
It could be hand-made and one-of-a-kind, but it's unlikely to have value as an artifact.