why did the copper on the statue of liberty turn green but copper mugs and copper pipes don’t?


why did the copper on the statue of liberty turn green but copper mugs and copper pipes don’t?

In: Other

Copper pipes do oxidize and turn green over time, especially in wet environments. I assume copper mugs do too if you don’t clean them regularly.

However it takes quite a while for a green patina to form on bare copper. According to some cursory googling it took the Statue of Liberty between 20 and 40 years to turn totally green. It was also completely exposed to rain, unlike most household copper piping, and industrial air pollution supposedly had an affect also.

Those copper mugs and pipes will eventually tarnish just like the statue of liberty. The green tarnish is the copper equivalent of red rust on iron. Just oxidation of a different metal.

There’s a pretty big difference between a piece of copper that has been fully outdoors in the middle of New York Harbor for almost two hundred years and a pipe that’s encased in a wall. Moisture and salinity are what contribute to copper corrosion; interior pipes are mostly protected from both because they’re enclosed in walls.

They do. Those things aren’t typically constantly exposed to the elements though, like the statue is.

As others have said, it’s mostly a matter of time and weathering factors. If you look at really old plumbing, it’s green, too. My grandma’s house was built in the late 1800s and had some original plumbing until at least the mid 1980s. I remember being in the basement and asking why she had green pipes instead of shiny copper like my (less than a decade old at that point) house. The answer was along the lines of “It’s really, really old and we’re too afraid to look at it very hard, much less actually try to replace it.”

For a slightly more modern example of large scale outdoor copper oxidation, check out photos of St Josephat’s Basilica in Milwaukee, WI. It was built about 125 years ago, and the roof of the dome is copper cladding similar to the Statue of Liberty. In the early 1990s, the roof was the classic old penny blue-green color. The cladding was completely replaced in 1997 and the shiny new copper was bright enough that it caused problems when the sun was at an angle to reflect into evening rush hour traffic.

If you look at current pictures, the roof has faded considerably and now resembles a not-old-but-not-new penny. It’s not bright enough to shine anymore (fortunately for those trying to stay on the road on that part of I-43), but it’s still a dark metallic color. In another few decades, the roof will be Lady Liberty Blue, and probably need to be replaced again in a century or so.

They definitely do as well.

My years old copper jug has streaks of that same green on it.

Old copper pipes will also have areas of that green color too, but usually in a much dirtier fashion as its usually the result of some local flaw causing moisture.

… How fast do you think this is supposed to happen?

In dry air, copper reacts with the oxygen in the air to form a reddish coating. Think “old penny”. In order to turn green, copper needs to get wet and then exposed to acids. These acids come from from dissolving air pollutants as well as carbon dioxide (C02) into the water. The acids then react with the copper oxide that first formed to make the green color. Copper pipes are generally dry on the outside. Without moisture, the air pollution and C02 can’t turn into an acid and so cannot attack the copper. Now copper utensils and pots and pans do get wet, but you don’t normally leave your pots and pans sitting in water for months at a time. Also kitchen items tend to get scraped and scrubbed so any green compounds probably just get rubbed off before they have a chance to build up.