A method of machining a cathode used in an electron gun. The methods use an acid gas resistant molecular sieve, and the sulfur-containing compounds are preferably selected from the group consisting of carbondisulfide, carbonylsulfide, and compounds within the formula YSX, wherein S is sulfur, and X and Y are the same or different and are independently selected from the group consisting of hydrogen, alkyl, aryl, oxygen, and alcohol. This allows a cost-effective component to be produced which reacts to electromagnetic radiation in a specifically defined manner.