Removing green copper oxides with Electrolysis, chemicals, etc.

[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?

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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.