Which Metals Turn Green? 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.

It all starts with knowing your metals and what color they eventually become. If you’re wondering which metals turn green … it all starts with a slow-moving special effect. Here's a closer look:

Which Metals Turn Green? The Patina Effect Explained

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 120 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 outermost layer 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 is a result of the copper coming into contact with water, oxygen, and carbon dioxide over time. This causes a coating to build on the surface. Yet, instead of rusting, it morphs into a beautiful blue-green color. 

And what's really cool about the blue-green color is that it also makes the metal more resistant to further corrosion. In a sense, when it oxidizes, it actually becomes stronger 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. If you walk down any street in America with lots of historic old buildings, chances are you'll see a lot of blue-green on the exterior facade.

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

What About Other Metals?

Does brass turn green? Does stainless steel turn green? What about other metals?

Let's knock stainless steel off the list first. This metal is known for its shiny aesthetic and resistance to rust. It's why many outdoor furniture pieces, car parts, and exterior structural components are built using stainless steel. It's essentially a "what you see is what you get" material -- no color change here.

Brass architecture, on the other hand, behaves a lot like copper when exposed to air and water — it'll take on a blue-green color. This is largely because about two-thirds of brass' makeup is actually copper — so it behaves in a similar way over time. Brass’s patina effect turns it a little more green; copper’s is a bit closer to blue.

Galvanized steel and aluminum are two other metals that change when oxidized, just not in the same way as copper and brass. 

Galvanized steel will actually take on a white-like color due to its high zinc content. Some builders call this “white rust.” Meanwhile, when aluminum is exposed to air, it forms a protective layer on itself, a process called 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 can be done rather simply -- 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.

Age may be more than a number when it comes to metals, but it’s still just one of many factors that should go into your material choices. To learn more about decorative metal, check out the free download below: