Any chemists in the house? Ammonia + copper =??

proud2deviate

proud2deviate

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Apr 5, 2004
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Hello, all. I was going to attempt to put a patina on som copper rings (for chainmail,) and after a little searching I found a method that suggested soaking for a day in a solution of vinegar and ammonia. So I put the rings in an old vodka bottle and doused them with good old under-the-sink dollar store ammonia. By the time I got back from the pantry with the vinegar, the solution had started to turn blue. Very very pretty deep blue. Curious, I decided to leave out the vinegar and see what might happen. A day later, my rings have taken on a matte finish (I suspect they're being disolved/etched,) and the solution has gone from blue to "Damn! That's BLUE!"

So, my question is, what do I have here, specificly? I did a search, and found a bunch of stuff about copper salts and ions, but nothing definitive. I also found that people have used this as a blue dye for cloth. Is it useful beyond that? Or particularly hazardous? (I don't plan on gargling with the stuff, but it never hurts to ask.)

Oh, and I figured out the patina. A few rings got caught at the top of the bottle (exposed to the air,) and turned greener than a seasick leprachaun :)
 
Well, since ammonia is NH3 and it's apparently dissolving the copper, I would guess you've got a solution of Copper(II) Nitrate . It doesn't appear to be anything too dangerous. You can probably flush it down the sink without any trouble, but don't get it in your eyes or on your skin, it's an irritant.
 
lots of copper salts and compounds are really pretty blue. Perhaps tetraammonium copper sulfate?

I can't locate an MSDS right this second, but it's used as a fungicide, and in current forms of pressure-treated lumber. It's probably toxic if concentrated, but not so awful if diluted.
 
It could also be (and now that I think of it it probably is) Copper(II) Hydroxide That would make more sense than Copper(II) Nitrate. Hopefully someone with more knowledge than I will come along to figure it out.

Edited to add: OK, I was wrong on both counts. A little google searching for copper and ammonia revealed the existence of something called copper ammonium complex, Cu(NH3)2, which makes the most sense of all.
 
Yes ammonia + copper will form a "complex" ...There should be a number of solutions available on the internet to produce a 'patina' on copper.
 
Okay, cool. Thanks a bunch, people! Very infomative.

Damn the luck, though. I could've used a fungicide a week ago. . .
 
on addition of a little ammonia to a copper solution you will get copper hydroxide
the complex only forms in excess ammonia
it gave a very nice deep blue colour, but the smell was a pissoff
 
Speaking of pissoff, that's exactly how they used to color copper and brass stuff. Yuk.
 
nah, not nitrates…
its copper-ammonia complex
Cu(NH3)4 2+ and some negatively charged ions (acetate, in yr case)
 
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