You are looking at TWO (2) White Porcelain Doorknobs from the early to mid 1800s. This particular doorknob set was salvaged from a farmhouse built around 1810 before it was demolished for housing. Included is the doorknobs, and also the shaft that connects them together. The doorknobs have some kind of patina on them that doesn't seem to want to come off. I'm not sure if they were made like this, or if this just came over time with wear.
All together the two doorknobs are 6" long, and each knob is 3 1/2" in diameter.