Manufacturing method for a sealing plug used in sealing an arc tube, sealing plug, and discharge lamp

A manufacturing method for a sealing plug used in sealing an arc tube, the sealing plug being formed from a plurality of sintered layers made of different components, the sintered layers being layered around an outer circumference of a metal lead wire, so that the layers are substantially concentric with respect to the metal lead wire, comprising:

• a slurry preparation step of preparing slurries that include the sintered layer components for each layer of the sealing plug;
• a preform manufacturing step of manufacturing a preform by dipping a core, which is substantially the same shape as the metal lead wire, into the slurry used to form an inner-most layer and drying the slurry adhering to the core, and repeating the dipping and drying sequentially for the slurries used to form a second layer to an outer-most layer;
• a preliminary sintering step of sintering the preform and burning-off the core by pyrolysis;
• and
• a main sintering step of inserting the metal lead wire in a space created by the burning-off of the core, and sintering the preliminarily sintered preform, so as to bond together the metal lead wire and the preform.