A couple points on Cleaning Copper and Galvanic Corrosion

[shifty803]

The first thing I wanted to bring to everyone's attention is this excerpt from a chemistry professor on the cleaning (de-oxidizing) copper. Vinegar by itself is surprisingly not that effective of a cleaner. However, vinegar and salt (acetic acid and sodium chloride) is highly effective for the following reason.

"In water, under any conditions, salt breaks down into sodium ions and chloride ions. (Even in the solid, it is in that form, so it would be better to say that the water just allows the ions to separate.)

It's a little more complicated than that. The copper in the tarnish would be in the 2+ form. Chloride ions do not bond strongly to this form. However, they do bond fairly strongly to the 1+ form. A reaction that would be unfavorable in the absence of chloride ions, Cu + Cu2+ *--> 2Cu1+, becomes favorable when the chloride is present to tie up the Cu1+ form (as [CuCl2]-).

The first process can be viewed as transfer of an electron from Cu (metallic copper) to Cu2+. This is followed by reaction of the Cu1+ with the chloride. The resulting copper-chloride complex is soluble in water. It's the electron-transfer aspect of the chemistry (the conversion of metallic copper and the Cu2+, to Cu1+) that makes the role of the salt a little surprising."

You can test this for yourself using 1 cent US pennies or 5 cent Euro coins like I did. The salt makes the cleaning process highly effective. A copper coin placed in this solution is cleaned almost instantly.

Edit: I took out what I said about the galvanic corrosion, because the metal plating is nickel, not zinc. But really, assuming you keep contaminates out of the loop, even the worst metals should be okay in just distilled water because of its almost nonexistent conductivity. Not sure how anti-algea stuff plays into it though.

[sykocus]

i don't think i've seen any zinc planted barbs, many are nickel plated.

[shifty803]

Ah you're totally right. I don't know how I got zinc in my head.

[Eastcoasthandle]

good read, this should be part of the sticky when cleaning your copper WBs. It is instantaneous.

[Burn]

Will this vinegar and salt solution etch the "good" copper away, or only the oxidized copper?

Excellent read, BTW

[Sparky]

Will this vinegar and salt solution etch the "good" copper away, or only the oxidized copper?

Excellent read, BTW

It might I suppose if left long enough. One way to find out is stick a newer US penny in the solution and see if the copper disappears down to the nickel/tin/whatever it is base metal.

[shifty803]

Yeah the article I found this in was referring to cleaning copper decorations, pots and pans, etc... Basically, stuff that would be impossible to immerse in a vinegar/salt solution anyway. They recommended using a paste of vinegar, salt, and flour for that sort of thing. I wish I had more chemistry in college so I could tell you for sure whether it would hurt the copper itself.

The only thing I can tell you is that I've left a euro coin and one of my blocks in the solution overnight and didn't notice anything adverse. To the naked eye, I couldn't see any difference from the initial few minutes, for better or worse.

Unfortunately, when you're talking molecules of copper, my naked eye observation may or may not have anything to do with what actually happened. :/

[shifty803]

One more thing to be aware of, although most of you probably know this already:

"When the vinegar and salt dissolve the copper-oxide layer, they make it easier for the copper atoms to join oxygen from the air and chlorine from the salt to make a blue-green compound called malachite."

That is why you MUST rinse your copper off immediately after cleaning, or that is what will happen.

Here is a cool little article on how this works, without going into equilibrium equations and fun chemistry stuff nobody understands.

http://www.exploratorium.edu/science_explorer/copper_caper.html

[Modzilla]

coca-cola, 20 minute soak, rinse thoroughly