Crystals having a modified regular tetrahedron shape are provided. Crystals preferably have four substantially identical triangular faces that define four truncated vertices and six chamfered edges. The six chamfered edges can have an average length of l, and an average width of w, and 8l/w9.5.

Crystals having a modified regular tetrahedron shape are provided. Crystals preferably have four substantially identical triangular faces that define four truncated vertices and six chamfered edges. The six chamfered edges can have an average length of l, and an average width of w, and 8l/w9.5.

Processes for fusing opaque fused quartz to clear fused quartz to form ultraviolet light transmission windows comprise surrounding a clear fused quartz ingot with an opaque fused quartz sleeve or opaque fused quartz particles, then heating the clear and opaque fused quartz together in a furnace, past the transition temperature of the opaque fused quartz, in order to join the two types of quartz together around the perimeter of the clear fused quartz ingot, but without substantial mixing beyond the interface.

Processes for fusing opaque fused quartz to clear fused quartz to form ultraviolet light transmission windows comprise surrounding a clear fused quartz ingot with an opaque fused quartz sleeve or opaque fused quartz particles, then heating the clear and opaque fused quartz together in a furnace, past the transition temperature of the opaque fused quartz, in order to join the two types of quartz together around the perimeter of the clear fused quartz ingot, but without substantial mixing beyond the interface.

Disclosed herein are glass-ceramics having crystalline phases including -spodumene ss and either (i) pseudobrookite or (ii) vanadium or vanadium containing compounds so as to be colored and opaque glass-ceramics having coordinates, determined from total reflectancespecular includedmeasurements, in the CIELAB color space of the following ranges: L*=from about 20 to about 45; a*=from about 2 to about +2; and b*=from about 12 to about +1. Such CIELAB color space coordinates can be substantially uniform throughout the glass-ceramics. In each of the proceeding, -quartz ss can be substantially absent from the crystalline phases. If present, -quartz ss can be less than about 20 wt % or, alternatively, less than about 15 wt % of the crystalline phases. Also Further crystalline phases might include spinel ss (e.g., hercynite and/or gahnite-hercynite ss), rutile, magnesium zinc phosphate, or spinel ss (e.g., hercynite and/or gahnite-hercynite ss) and rutile.

Disclosed herein are glass-ceramics having crystalline phases including -spodumene ss and either (i) pseudobrookite or (ii) vanadium or vanadium containing compounds so as to be colored and opaque glass-ceramics having coordinates, determined from total reflectancespecular includedmeasurements, in the CIELAB color space of the following ranges: L*=from about 20 to about 45; a*=from about 2 to about +2; and b*=from about 12 to about +1. Such CIELAB color space coordinates can be substantially uniform throughout the glass-ceramics. In each of the proceeding, -quartz ss can be substantially absent from the crystalline phases. If present, -quartz ss can be less than about 20 wt % or, alternatively, less than about 15 wt % of the crystalline phases. Also Further crystalline phases might include spinel ss (e.g., hercynite and/or gahnite-hercynite ss), rutile, magnesium zinc phosphate, or spinel ss (e.g., hercynite and/or gahnite-hercynite ss) and rutile.

In order to improve the yield of an optical fiber base material, provided is a manufacturing apparatus for manufacturing an optical fiber base material by forming a soot deposition body on a surface of a target rod, including a main burner that generates glass microparticles to be deposited on the target rod while moving in a longitudinal direction of the target rod; a pair of side burners that are arranged outside a movement range of the main burner and heat both ends of the soot deposition body formed on the surface of the target rod; and a shielding member that prevents the glass microparticles generated by the main burner from being deposited on the target rod farther outward than a segment of the target rod sandwiched by the pair of side burners.

A process for producing a fluorinated quartz glass is described, including providing an SiO.sub.2 soot body; reacting the SiO.sub.2 soot body with a fluorinating agent having a boiling point of greater than or equal to 10 C. to obtain a fluorinated SiO.sub.2 soot body; and vitrifying the fluorinated SiO.sub.2 soot body.

A process for producing a fluorinated quartz glass is described, including providing an SiO.sub.2 soot body; reacting the SiO.sub.2 soot body with a fluorinating agent having a boiling point of greater than or equal to 10 C. to obtain a fluorinated SiO.sub.2 soot body; and vitrifying the fluorinated SiO.sub.2 soot body.

A quartz glass crucible 1 having a cylindrical side wall portion 10a, a bottom portion 10b, and a corner portion 10c includes a transparent layer 11 as an innermost layer made of quartz glass, a semi-molten layer 13 as an outermost layer made of raw material silica powder solidified in a semi-molten state, and a bubble layer 12 made of quartz glass interposed therebetween. An infrared transmissivity of the corner portion 10c in a state where the semi-molten layer 13 is removed is 25 to 51%, the infrared transmissivity of the corner portion 10c in the state where the semi-molten layer 13 is removed is lower than an infrared transmissivity of the side wall portion 10a, and the infrared transmissivity of the side wall portion 10a in the state where the semi-molten layer 13 is removed is lower than an infrared transmissivity of the bottom portion 10b.