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  #1  
Old 02-06-2018, 11:30 PM
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Default Cleaning copper - If you want to

I got interested in a thread by Fool on cleaning sulfur residue off copper. I know there are a lot of cases where one wouldn't want to touch the patina on a metal, and I'm not suggesting doing anything in those cases.

I mentioned in that thread a well known method I had used for silver, where you put the tarnished silver on a piece of aluminum foil, submerged in a dish of dissolved baking soda. It works, transferring the sulfur to the aluminum, and not dissolving or scrubbing off any silver.

I thought it might work on copper. I don't know whether copper patina is really sulfide, or just an oxide - maybe it can be either. But anyway, I thought it was worth a try.

But it doesn't work. Left it overnight, nothing happened.

But I thought of some other ways to take the oxide coating off without dissolving any copper. I know passing hydrogen gas over hot copper will take the oxide off in a jiffy - like instantly, like magic. But that's a little risky for home use.

So I thought of another reducing agent (technical term, just means something that reverses oxidation/corrosion) - thiosulfate ion, a.k.a. "hypo" or "fixer" in black and white photography. It's low toxicity (it's an important medicine) and not corrosive. It's easy to get, and safe to dispose of. Once made the solution should keep -- just label it and keep it away from kids, of course.

So today, I got three pennies with solid oxide/patina... Name:  IMG_8839.jpg
Views: 850
Size:  20.5 KB
I put them in about a half cup of water with a tablespoon of sodium thiosulfate (pentahydrate form, but it doesn't matter once it's dissolved), and stirred. Name:  IMG_8841.jpg
Views: 824
Size:  24.4 KB
In just minutes they were looking cleaner. In about 20 minutes I took them out, dried them, and polished them a bit on a soft cloth.Name:  IMG_8845.jpg
Views: 830
Size:  25.4 KB
There was no blue tint to the solution, so no copper got dissolved. The black patina was gone. Some verdigris (green corrosion) was not removed from one penny, so I put that in weak HCl (about a 1:4 dilution of plumber's muriatic acid, which doesn't react with metallic copper) for about 5 minutes (getting to be dinner time, or I'd have left it a little longer,) and that mostly came off. I used a soft pencil eraser on it, too.
Name:  IMG_8840.jpg
Views: 814
Size:  19.2 KB
The backs:
Name:  IMG_8844.jpg
Views: 833
Size:  25.9 KB

As I say, I know this isn't appropriate for coins of historic value, would harm the value of collectibles, and a lot of us (me included) like the patina. But I thought someone might find it useful for "non-historic" applications.

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  #2  
Old 02-07-2018, 04:59 AM
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Hey now THAT was a well thought out experiment with great results! Thanks for the pics and the write up!

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Old 02-07-2018, 08:40 AM
gldndrms gldndrms is offline
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Really interesting! I just might have to play with this soon!

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Old 02-07-2018, 01:29 PM
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Thanks alot, im going to test this on a few junk ones as soon as i can get this chemical! I have lots of old wheaties that are heavily covered in black due to the sulfur in the air. Ill let you know how it works.
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Old 02-08-2018, 04:58 PM
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I use this at work but you can get all kinds of sizes of bags of sodium thiosulfate from a popular online shopping network for cheap. A pound for 8.95...

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Old 02-15-2018, 05:28 PM
gldndrms gldndrms is offline
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Just curious - does this emit any gas/fumes that I need to be aware of?
I ordered some and it should be delivered tomorrow. I can't wait to start playing

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  #7  
Old 02-15-2018, 06:04 PM
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I used it at room temperature, and it emitted no fumes. Don't heat it. There's no need to. It would create fumes if you heated it, so don't. Don't combine it with other chemicals. Do not combine it with oxidizing agents. Don't breathe the dust, of course.

It's the same chemical used by millions of people for a hundred years for black and white photography, as "fixer", a.k.a. "hypo". No chemical should be handled without understanding safe handling practices, of course. But the safety info out there is widely available, so take a look at that, and you should be safe.

Safety info on this page... https://www.baylor.edu/ehs/index.php?id=94373

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Old 02-16-2018, 10:37 AM
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Great write up. I wish I would have seen this before destroying some Indians.

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  #9  
Old 02-16-2018, 08:57 PM
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Cool idea! Thanks for sharing!

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Old 04-01-2018, 01:51 PM
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Arthur, sounds like you are chemist (so is my wife) and she reinforced your experiment. She actually thought is was hard to get sodium thiosulfate but it is available from the retailer that happens to be under attack but Trump .

So I just tried the hydrogen peroxide method on some of my coins and it worked pretty well, along with some light toothpick work and Qtips. I will have to give this a try.

Thank you.

Originally Posted by ArthurEvans View post
I got interested in a thread by Fool on cleaning sulfur residue off copper. I know there are a lot of cases where one wouldn't want to touch the patina on a metal, and I'm not suggesting doing anything in those cases.

I mentioned in that thread a well known method I had used for silver, where you put the tarnished silver on a piece of aluminum foil, submerged in a dish of dissolved baking soda. It works, transferring the sulfur to the aluminum, and not dissolving or scrubbing off any silver.

I thought it might work on copper. I don't know whether copper patina is really sulfide, or just an oxide - maybe it can be either. But anyway, I thought it was worth a try.

But it doesn't work. Left it overnight, nothing happened.

But I thought of some other ways to take the oxide coating off without dissolving any copper. I know passing hydrogen gas over hot copper will take the oxide off in a jiffy - like instantly, like magic. But that's a little risky for home use.

So I thought of another reducing agent (technical term, just means something that reverses oxidation/corrosion) - thiosulfate ion, a.k.a. "hypo" or "fixer" in black and white photography. It's low toxicity (it's an important medicine) and not corrosive. It's easy to get, and safe to dispose of. Once made the solution should keep -- just label it and keep it away from kids, of course.

So today, I got three pennies with solid oxide/patina... Attachment 406034
I put them in about a half cup of water with a tablespoon of sodium thiosulfate (pentahydrate form, but it doesn't matter once it's dissolved), and stirred. Attachment 406035
In just minutes they were looking cleaner. In about 20 minutes I took them out, dried them, and polished them a bit on a soft cloth.Attachment 406036
There was no blue tint to the solution, so no copper got dissolved. The black patina was gone. Some verdigris (green corrosion) was not removed from one penny, so I put that in weak HCl (about a 1:4 dilution of plumber's muriatic acid, which doesn't react with metallic copper) for about 5 minutes (getting to be dinner time, or I'd have left it a little longer,) and that mostly came off. I used a soft pencil eraser on it, too.
Attachment 406037
The backs:
Attachment 406038

As I say, I know this isn't appropriate for coins of historic value, would harm the value of collectibles, and a lot of us (me included) like the patina. But I thought someone might find it useful for "non-historic" applications.

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  #11  
Old 04-05-2018, 08:14 PM
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Well I tried what the OP recommended and maybe I didn't add enough of the chemical, but it did not work. I tried 3 times with moderate results, maybe a little bit cleaner but I can say that hydrogen peroxide seems to work better. Your results may vary.

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  #12  
Old 04-07-2018, 10:10 AM
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Just started using this method for cleaning pennies. First small batch, the only real copper one was a 1975, and it came out looking great.

It did help, somewhat, to clean up my zincolns. But, many are still pretty nasty looking, and a number where it's falling apart at the edges. What do people do with these, just throw them away? Roll them and turn them in at the bank??

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