cleaning off sulfur residue

Fool

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Sadly my mother passed away 2 years ago, i moved most of the stuff out of the house into mine due to high sulfur in the air from the well water. I finally got around to going through the coin collection and a lot of the coins are black from sulfer, mostly wheat pennies. Is there a good, safe way to clean them? I doubt any are worth a lot I just want to clean them up so they don’t get worse…
 
Sorry to hear about your mother. Unfortunately I don’t think you can harm them any cleaning them because sulfur eats copper pretty bad. If they are black I would be willing to bet that the copper is pitted as well.
 
I've used this on silver. Seems like it ought to work on copper, but haven't tried it myself.

http://scifun.chem.wisc.edu/HomeExpts/tarnish.html

It may work but the chemical reaction will be different...


3 Ag2S + 2 Al --/> 6 Ag + Al2S3
silver
sulfide aluminum silver aluminum
sulfide

It will actually be :

CuS + Al --/> Cu + Al2S3
Since it is an electrochemical reaction it should work since Copper is a good conductor. I guess only one way to find out.
 
It does seem like it ought to work, but it doesn't. I've just done a trial, overnight, with tarnished pennies, following the silver method above. I think the difference is that silver has a much higher reduction potential than copper... Also, although copper does have a high affinity for sulfur (that's why they use it so much in liquor stills, it takes out sulfur and cleans up the flavor), most of the tarnish/patina on copper is probably copper (II) oxide.

I've got some other ideas, though, that I'm going to test out. One I've done before is heating the copper in hydrogen gas, but that's not practical unless you're in a lab! So I'm going to see if I can find some less explode-y methods that might help.... I'll post here if I come up with anything that can be reasonably done at home.
 
I've used this on silver. Seems like it ought to work on copper, but haven't tried it myself.

http://scifun.chem.wisc.edu/HomeExpts/tarnish.html

Thanks for posting this. I just tried the method outlined in the link on a Merc that was in pretty rough shape - more oxidation than any other silver that I’ve dug. I needed to reheat the solution several times as the directions suggested, but overall, the results were pretty good! Much of the black oxidation is gone!

Some before and after pics are below:
 

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Adding additional pics of the same cleaned Merc dime with better lighting:
 

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