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Question for you chemists


Konrad
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Why is it that copper roof sheathing will develop a patina and eventually turn black and then green, but not copper piping inside buildings?

At first I thought maybe it's because of UV, but the copper roofs I see installed all discolor uniformly regardless of their orientation to north/south.

So what's the difference between inside and outside? Copper is copper, right?

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Originally posted by Konrad

Why is it that copper roof sheathing will develop a patina and eventually turn black and then green, but not copper piping inside buildings?

So what's the difference between inside and outside?

Rain, perhaps?

Rain + air (exposure) = oxidation?

Water sealed in a pipe - air (exposure) = no oxidation?

Can you tell I'm guessing?

Brian G.

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Oxidation is the key. Water on the surface of the copper is necessary in order to cause this chemical reaction. Other than the relative humidity in contact with the outside surface of copper water piping within a dwelling there isn't a sufficient water source for oxidation to take place. I remember this from inorganic chemistry 101 about 40 years ago. Or maybe it's 45 years in which case I don't remember sh-t.

NORM SAGE

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I think it has to do with the acids in the exterior air that are there as a result of combustion processes. The copper pipe will turn the same green wherever the acid from soldering flux gets on it and the air around us is heavy with hydrocarbons that contain various acidic compounds.

ONE TEAM - ONE FIGHT!!!

Mike

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Hi Jim,

I don't mean the gaseous makeup of air, I'm talking about the man-made contaminants that we and nature dump into the outside air that we aren't exposed to indoors. We burn coal and oil for electricity which returns to the surface in acid rain and affects the outdoor environment a great deal. Then you have tannic acid from trees and oxalic acid from algae and mosses, plus all of the hydrocarbons from automobile exhaust, none of which you have in the atmosphere of your home. Have you ever noticed that a raindrop or a snowflake tastes bitter?

We see copper pipe that is normally less than 100 years old, but other copper inside of older buildings, such as hinges, does develop a green patina - it just takes a lot longer indoors than outside. I think oxidation outside is more prevalent because it's sped up by contaminants in the air that mix with rain and disperse it through the exterior atmosphere more than inside.

The Katenizer can probably nail it.

ONE TEAM - ONE FIGHT!!!

Mike

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Ammonia will give copper the most amazing deep green patina, and not the "fluffy" patina; it's the deep patina that doesn't rub off on your clothes. Pouring the ammonia on the copper won't due it; you have to "fume" the copper w/ the ammonia gas. It takes several days, but it is a nice way to quickly "color" copper.

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Originally posted by Jerry Simon

Just saw some real shiny copper inside a home and wondered the exact same thing...why still so shiny? How weird is that?

Also just paid a bill of $54.99 with...get this, check #5499...can you stand it!

Jerry, bad news old boy. That means you're going to die a slow, horrible death in the near future. There's only one way out of it, which I'll be happy to share with you. Just send me $10,000 before it's too late, and I'll take care of it. [:-mischievous]

Brian G.

Semi-Professional Curse Lifter [:-witch]

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Originally posted by Konrad

Why is it that copper roof sheathing will develop a patina and eventually turn black and then green, but not copper piping inside buildings?

At first I thought maybe it's because of UV, but the copper roofs I see installed all discolor uniformly regardless of their orientation to north/south.

So what's the difference between inside and outside? Copper is copper, right?

Actually, no. The copper products we use are alloys. Tubing and roofing are different alloys, I'm sure.

However, this probably doesn't make much difference to your question. I pretty much agree with everyone else. The roof is exposed to all sorts of contaminants that the stuff inside and under the house never sees.

- Jim Katen, Oregon

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Professional Roofing magazine had a cool article on a similar issue this past month. Check it out. (NRCA's rag). I've been driving around looking for these evidences. (Why does exterior copper sometimes corrode and sometimes not...that was the drift of the article). Acid rain was the cause on the East Coast... check it out.

R

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