We have evaluated the cold-field-emission characteristics of HfC(100) and ultrasharp tungsten emitters. We found that proper acetylene treatment improved both the angular current confinement and the emission stability of thermally cleaned HfC(100) tips. Stable emission exceeding 10 mu A/sr for over 1 h and angular confinement to a 3 degrees semicone angle have been observed, The improvements are probably related to the modified work function and surface chemical composition induced by the acetylene treatment at the tip apex, Carburization of W(100) acid W(111) tips also significantly improved the emission current stability. This study indicates the usefulness of surface processing in the development of cold-field emitters.