Polishing on smooth ground glass plates allows the condition of the polishing material to be tightly controlled for optimum cleanliness. In addition, the use of deagglomerated alumina of small particle size (0.05 μm) allows for a more scratch free active electrode surface. The use of particles of even smaller size (0.007 μm fumed silica) should enhance the smoothness and activity. If this does not activate the surface, re-polishing with larger particle size abrasive, such as 0.25 :m diamond, followed by 0.05 :m alumina or 0.007 :m silica.