Abstract Field emission microscopy has been used to determine the location and brightness of the tip apex protrusion. We report that (100) oriented tungsten single crystal tips produce highly stable field emission currents after zirconium oxide processing. In zirconium oxide processing we have adapted electron bombardment heating for sintering zirconium powder on the W-tip. It is a very simple method which is better than the wire sintered method. In addition, zirconiating has been very well achieved by heating in an oxygen atmosphere of 10−8 Torr which fixes the protrusion on the tip apex. The micro protrusion formed only one bright spot on the (100) plane if zirconiating was carried out by Zr/W(100). Even after they were exposed to atmosphere for a long time a reoperated Zr/W cathode tip which has a micro-protrusion reproduced the original property as an emitter source with a high optical brightness spot at the tip apex.