Abstract: A method and apparatus for forming an insulator 62 on one major surface of a uniaxial tension focus mask 25 includes the steps of: positioning a mask sheet 27, having a multiplicity of openings 42 that extend from a first major surface of the mask sheet through a main body portion thereof to an oppositely disposed second major surface, at a distance from a charging gun 72, 172 having a source 74, 174 of a dry-powdered insulative material; charging and directing the dry-powdered insulative material toward the first major surface of the mask to provide a coating of the charged, dry-powdered insulative material thereon, and providing means 70, 272 for preventing the charged, dry-powdered insulative material from extending into the openings 42 and being deposited onto the main body portion of the mask surrounding the openings and the second major surface.