Similar to another knob, but this one appears to be made of iron. It is prominent against the unpainted door.
No matter where you look on the streets of Paris, there are beautiful things to catch your eye and record with your camera. I became obsessed with door hardware on my last trip, probably because it relates so closely to the fittings that drive our business. There are examples of fine craftsmanship, centuries old, softened with age and polishing. Even the examples that have been painted still have beautiful silhouettes and create wonderful shadows on the aged and painted wood.