PRODUCTION METHOD OF GLASS PREFORM

PROBLEM TO BE SOLVED: To provide a production method of a glass preform capable of preventing heat deformation of a quartz core tube, even in the case where the quartz core tube is not crystallized (devitrified) when dehydrating/sintering the glass preform.SOLUTION: In a production method of a glass preform 12 for making the glass preform 12 transparent by heat treatment after inserting the glass preform 12 into a quartz core tube 2, the first heating temperature at which heat treatment is performed before devitrification of the quartz core tube 2 is set at a lower temperature than the second heating temperature at which heat treatment is performed after the devitrification of the quartz core tube 2. 【課題】ガラス母材を脱水・焼結処理する際に、石英炉心管が結晶化（失透）していない場合でも石英炉心管の熱変形を防ぐことができるガラス母材の製造方法を提供する。【解決手段】ガラス母材１２を石英炉心管２内に挿入し、加熱処理によりガラス母材１２を透明化するガラス母材１２の製造方法であって、石英炉心管２が失透する以前に前記加熱処理を行う第１加熱温度を、前記石英炉心管２の失透後に前記加熱処理を行う第２加熱温度より低い温度とするガラス母材の製造方法。【選択図】図１