Quezal Lamps

Q: I have a set of 20 small Quezal lamp shades hanging from original brass fixtures that have been in my house since it was built in 1910. The living room and dining room each have a center fixture with four shades and there are single-shade fixtures at the corners of each room. There are two single-shade sconces above the fireplace mantel and a two-shade fixture in the foyer. The shades are in great condition (except for dust) and I’m wondering how I can determine the value of these lamp shades.