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Patinas & The March of Time

Previously, we featured a custom curtain rod job which was left unlacquered, so it would patina over time. Well, we had a couple of extras, so let’s check in on how they are aging.

For a refresher, here is what one of the rings looked like on its way out the door:

And here is what one looks like now:

The color is a little darker, a little deeper, but there is still a bit of shine to it. I have one more experiment brewing, though – I have one ring at my desk which I handle from time to time, exposing it to finger oils. Here is what it looks like:

It’s darker still. And on top of that its color has flattened out, removing any kind of shine. So what the heck is going on here?

What we are witnessing is the formation of a natural patina, which is synonymous with tarnish. Unlike silver, however, it can be desirable when it forms on copper and copper-based alloys like brass and bronze. The surface of the metal is oxidizing, and a combination of chlorides, sulfides, and carbonates are forming which both darken the color and protect the metal underneath the surface from the same fate. That’s right – unlike iron-based metals like steel, oxidation on copper alloys prevents further oxidation.

Since the rings are inside, and not subjected to the elements, the process is much slower than if they were left outside. The one I’ve been handling, however, is a bit more advanced in the process due to oils transferred from my hand. Even still, at this rate it will take several decades to go through a series of deepening browns before turning green, which is a particular patina known as verdigris.

So stay tuned for the next few dozen updates in this series, which should wrap up some time in the 2040s. In the mean time, feel free to ask any questions you have in the comments below, or send us an email.

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