What are door knobs and locks and hings made of?

Much residential door hardware is made of brass. However, depending on the quality of the hardware more brass or less brass is used. High quality hardware (for example Baldwin Hardware or Hager Hinge) is made of heavy gauge (thickness) tarnish & scratch resistant brass. Lower quality hardware (for example Kwikset and store branded hardware) is made of thin gauge (thickness) brass. Sometimes lower quality hardware is brass clad steel or brass plated steel.