It is metal. The homeowner added a beautiful rust patina finish with a mix of vinegar, hydrogen peroxide, and table salt.

Matthew Gallant - do you happen to know what type of metal? Copper reacts amazingly to the patina recipe you described, but hot rolled steel might react similarly. Just curious the specific starting point on this one. Ammonia also works great and reacts/interacts good with salt.

That's a great point, webchimp. I'll ask the architects and see if they know the exact material.

Thanks - I appreciate that. I ask because I'm sincerely interested. I'm working on a couple of furniture pieces and I'm using copper accents, but I've recently remodeled my fireplace to include hot rolled steel. If I can get that kind of patina out of the (already quite lovely) color variation in the steel, I'd be all over it!