Vintage Gatehouse solid brass round shaped hall & closet doorknob.  Model number 226017-TLT30.  Will not tarnish. 

Fits door thickness: 1 3/8-inch or 1 3/4-inch.   Latch fits standard door 2-3/8 or 2-3/4 backset.
Easy replacement install with just a screw driver.  Concealed screws for an elegant appearance.