From international metallography society symposium on specimen preparation for metallography; Los Angeles. California, USA (23 Sep 1973). A triode cathodic vacuum etcher has been developed that has a number of advantages over conventional diode etchers. The triode etcher can be operated at specimen voltages well below 1000 V(dc) to minimize mount deterioration and the danger of arcing to the etched surface. Etching voltage and current density can be independently varied so that high current densities can be used with low voltages to provide rapid etching rates while minimizing heating of the specimen. Also. redeposition of sputtered material on the etched surface is reduced because of the low operating pressure (<3 millitorr) of the triode system. At very low voltages (75 to 125 V(dc)) the etching rate is relatively insensitive to crystalline orientation and a polishing action is obtained. This permits the removal of deformed surface layers and even such gross surface defects as the scratches from 600-grit paper without producing significant surface relief. This ion polishing capability has been used to reveal the pore structure of UO/sub 2/ and UO/sub 2/-PuO/sub -specimens by removing surface flow material without enlarging the pores. Details of the design and operation of a simple, …