How you clean a door knob depends on the metal and finish of the knob. Generally, do not use harsh chemicals or abrasive materials on the door knob, as this could damage the finish. Brass and copper door handles can be cleaned with a salt, vinegar, and flour mixture. Stainless steel doors can be cleaned with mild soap and water. General purpose cleaners can be used on crystal door knobs. Pewter door knobs can actually be cleaned with white cabbage leaves (the leaves help bring out the shine in pewter).