25 November 2010

Thanksgiving re-runs: So what the devil's a living finish anyway?

I'm taking a few days off to celebrate Thanksgiving and in lieu of writing a post a day over the holiday, I'm going to run a series on faucet finishes I wrote in February '09. Happy Thanksgiving one and all!



I had a similarly phrased question from a reader the other day and it's sent me on a quest to find out. As luck would have it, I'd already set up an interview with a finish developer from Kohler prior to being asked that living finish question, so I asked the source directly and I learned a thing or two.

That Kohler conversation gave me a ton of information to write about by the way, so look for a series on plumbing fixture finishes over the course of the next week or so. But in the meantime, here's a little something I learned about metals and patinas.

This is copper.


This is what happens to copper when it's exposed to the elements. Copper reacts to acids and alkalis in the environment to form a variety of chlorides, sulphides and carbonates known collectively as verdigris. That's French for green gray. Verdigris is composed of  copper carbonate or copper chloride primarily and those chemicals make up the green patina most people associate with copper. 


Copper is a highly reactive metal that's almost never used in its pure form. Generally, copper's combined with another metal to make it stronger and a little less reactive. When copper's combined with tin the result is bronze. These are bronze ingots.


When copper's combined with zinc the result is brass. And here's what raw brass looks like.


Due to their copper content, both metals retain a lot of the reactivity inherent in copper, though it's a bit less pronounced.

So here's what happens when bronze is left to its own devices. It turns a warm brown with yellow tones. These are the doors to the Pantheon in Rome and they're about 1800 years old. They're also the color of dark chocolate.


Brass on the other hand goes golden brown with a slight greenish tone to it.


These naturally occurring patinas are what's meant by a living finish. These patinas take time to develop and really, they never stop developing. After all, they're an ongoing chemical reaction.

When it comes to faucets; copper, bronze and brass are never left in their natural states to be allowed to age into their natural patinas on their own. It can get confusing because most manufactured faucets and fixtures have a patina applied to them. Let's back up for a sec though.

If you remember your basic chemistry, an alloy is the mixture of two or more metals. Alloys like brass and bronze aren't categorized scientifically, and there aren't any standard recipes for these metals. On top of that, copper never shows up in its pure state --it too is usually an alloy that's made mostly of copper. Add to that that the natural process of oxidation is called a patina, but so is virtually any color applied to a base metal. Argh.

I'll dig into this a little further tomorrow, but for now just remember that a living finish is a finish that will age and change color with time. On purpose.

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