I recently visited the Phil. Museum of Art and spent a few hours drooling quietly in their arms and armor collection. They have a small room filled with some highly decorated antique firearms and accoutrements. Here are some photos. Please forgive the quality - I was shooting with a compact camera in a darkened room through glass.
The least decorated were a pair of long rifles, one a swivel breech. It was listed as circa 1810 and engraved with "Orwigsburg/scul. Co Pa" (Schuylkill County).
There was a magnificent rifle made in Spain in 1758 by Josiah Zelaia, with gold wire inlay all over the barrel. I think I know where Thomas Curran got some of his inspiration.
Note the interesting rear sight design witht he integrated escutcheon.
I love the way even the tang screw is an opportunity for decoration.
Here's some amazing relief carving on a pistol from the same era. Sorry, I don't remember the provenance.
That is just a taste of it. There are matchlocks with pastoral scenes in ivory and mother of pearl. There are fine examples of wire inlay. It kept my attention for a while.
Oh yes, and the other 99% of the museum is worth your time as well.