In known methods for producing a glass component, a void-containing intermediate product containing doped or non-doped SiO.sub.2 is inserted into a sheath tube composed of glass, which has a longitudinal axis and an inner bore, and is thermally treated therein. In order to subject the intermediate product to a thermal and/or reactive treatment that is reproducible and uniform in its effect from this starting point, it is proposed in one embodiment that into the sheath tube's inner bore a first gas-permeable gas diffuser is inserted which is displaceable along the sheath tube's longitudinal axis and is pressed against the intermediate product during the thermal treatment.

A system and method for nitridizing a glass article includes supplying a source of a nitridizing gas including gaseous NH.sub.3 to a glass article supported within a furnace assembly and heating the glass article. In some embodiments, the system includes a handle assembly configured to support the glass article within the furnace assembly and a gas supply conduit carried by the handle and configured to supply the nitridizing gas to the glass article. In some embodiments, a method of nitridizing a glass article includes supplying the nitridizing gas such that a residence time of the nitridizing gas at temperatures greater than 500 C. corresponds to a predetermined time period. In some embodiments, a method of nitridizing a glass article includes supplying the nitridizing gas such that the glass articles is exposed to the nitridizing gas within a contact time t.sub.c.

A wire-drawing optical fiber base material manufacturing method of heating an optical fiber base material by a heater and forming a drawing shape portion at an end portion. The manufacturing method includes: forming, by a flow-regulating member disposed adjacent to the heater, a gas flow such that formation, along a surface of the optical fiber base material, of a flow of a gas containing a Si compound generated from the optical fiber base material heated by the heater is inhibited; and forming, while maintaining the gas flow, the drawing shape portion by pulling part of the optical fiber base material softened by being heated by the heater.

A wire-drawing optical fiber base material manufacturing method of heating an optical fiber base material by a heater and forming a drawing shape portion at an end portion. The manufacturing method includes: forming, by a flow-regulating member disposed adjacent to the heater, a gas flow such that formation, along a surface of the optical fiber base material, of a flow of a gas containing a Si compound generated from the optical fiber base material heated by the heater is inhibited; and forming, while maintaining the gas flow, the drawing shape portion by pulling part of the optical fiber base material softened by being heated by the heater.

Provided is a method for manufacturing an optical fiber glass preform in which a refractive index distribution is stable in a longitudinal direction of the glass preform. A method for manufacturing an optical fiber glass preform includes: depositing a porous glass preform by a vapor phase method; and sintering the porous glass preform in a heating region, when sintering the porous glass preform, the porous glass preform being inserted into a vessel of a sintering furnace, and an inside of the vessel being heated with a heater installed on an outer periphery of the vessel to form the heating region. The sintering is started after a surface temperature difference of the porous glass preform in a longitudinal direction is made 50 C. or lower.