In order to prepare a good secondary electron emitting surface from a silver‐magnesium alloy, it was found that baking in dry oxygen would not form the desired surface as originally believed, whereas baking in the presence of water vapor did yield a good secondary emitter. Subsequent experiments showed that, because of the rapid diffusion of oxygen through heated silver, the magnesium in the alloy was oxidized in situ without diffusing to the surface to form the required magnesium oxide layer. With water vapor as an oxidizing medium, the diffusion rate of magnesium through the silver greatly exceeded that of the water vapor, and a satisfactory surface layer was formed. A new technique was then devised in which an original water‐vapor process formed the desired surface, followed by an oxygen process to oxidize the remanent magnesium throughout the volume of the alloy. With the new technique, good secondary emitters are possible which will withstand severe overheating without the evaporation of magnesium found with earlier techniques.