Green Metal?! Discovering the Patina Effect

Like with many other things in life, age is a big talking point in decorative metals. Is youthful glow better, or is the weather look of experience more desirable? 

Each architectural metal has a different response to aging. Don't be concerned; this is normal -- and maybe even good! Regardless of whether you prefer shiny or tarnished looks, you need to be aware of the difference between brand-new architectural metal now and one affected by corrosion and oxidation. Some metals rust while others slowly turn green.

This transformation should be part of your decision marking process when choosing metal mouldings for your next architectural project. 

What causes green metal? It all begins with a slow-moving special effect. Here's a closer look:

How The Patina Effect Creates Green Metal

Think of the Statue of Liberty for a moment. What color is it? If you answered "green, with maybe a little blue," you're correct … but you wouldn’t have been 140 years ago.

Copper, bronze, brass, and other metal used in interior design and architecture may not look the same color 5, 10, 20, or even 50 years from now as they do today. So, what is it called when metal changes color? The patina effect -- a color change in red metals caused by oxidation.

The Statue of Liberty isn't made out of a green metal; its surface is mostly copper — and copper doesn't come out of the mill looking green. The Statue of Liberty is green thanks to the copper patina effect. 

Essentially, the green color results from the copper coming into contact with water, oxygen, and carbon dioxide over time, causing a coating to build on the surface. Yet, instead of rusting, it morphs into a beautiful blue-green color. 

And what's interesting about the blue-green color is that it makes the metal more resistant to further corrosion. In a sense, when it oxidizes, it becomes strengthened and more durable.

Aside from the Statue of Liberty, you'll commonly see roofs, outdoor sculptures, and even gutters made of copper due in part to the trademark blue-green color it eventually takes on. Walking down any street in America with historic old buildings, you'll often see a lot of blue-green on the exterior facade.

Of course, copper is just one metal that turns green.

Are There Other Green Metals?

Brass architecture, however, behaves similarly to copper when exposed to air and water — it'll take on a blue-green color. Because brass is two-thirds copper — so it behaves similarly over time. Brass’s patina effect is a little more green; copper’s color is closer to blue.

Galvanized steel and aluminum also change when oxidized, just not in the same way as copper and brass. 

The high zinc content in galvanized steel will cause it to take on a white-like color. Some builders call this “white rust.” Meanwhile, when aluminum encounters the air, it forms a protective layer through a process known as anodization. Ultimately, there’s little change in its color.

Aging Can Be Beautiful, Too

Another neat thing about working with metal is that you can age metal intentionally, so the design has a “classic” look with no waiting required. This process is simple -- all you need to do is buy a patina aging solution, which helps oils build up on the surface. The blue-green color will form in days rather than years. 

You can also place a jar of ammonia near copper or brass workpieces to get a patina more cheaply.

More on Materials Choices

Do you think aged metal is like a fine wine? Or do you prefer a mirrorlike or polished look? It’s all possible with metal mouldings and other design elements. 

The best way to see if a particular metal moulding will work for your project is to experience it in person. You can request a sample moulding by clicking below:

(Editor's note: This article was originally published in November 2019 and was recently updated.)