Abstract: An induction furnace (60) for reflowing a portion of an optical preform (12) in order to draw a lightguide fiber (11) therefrom includes a tubular susceptor (80) which is disposed centrally within a beaker (75) and a sleeve (82) which is disposed concentrically about the susceptor. The sleeve is spaced from the susceptor and is surrounded by insulating grain (83). A high frequency coil (84) is energized to couple its electromagnetic field to the susceptor to heat and reflow a portion of the preform. The movement of contaminating particles of the insulating grain into the interior of the susceptor is prevented substantially by annular, felt-like discs (91, 105) at the bottom and top of the beaker. The discs collect particulates which move downwardly and upwardly and because of their compliant engagement with the beaker and with the sleeve, they provide seals at those interfaces.