A quartz glass crucible 1 having a cylindrical side wall portion 10a, a bottom portion 10b, and a corner portion 10c connecting the side wall portion 10a and the bottom portion 10b to each other includes a transparent layer 11 made of quartz glass, and a bubble layer 12 made of quartz glass and formed outside the transparent layer 11. A ratio of an infrared transmittance of the corner portion 10c at a maximum thickness position of the corner portion 10c to an infrared transmittance of the side wall portion 10a is 0.3 or more and 0.99 or less, and an absolute value of a rate of change in infrared transmittance in a height direction along a wall surface of the crucible from a center of the bottom portion 10b toward an upper end of the side wall portion 10a is 3%/cm or less.

A quartz glass crucible 1 having a cylindrical side wall portion 10a, a bottom portion 10b, and a corner portion 10c connecting the side wall portion 10a and the bottom portion 10b to each other includes a transparent layer 11 made of quartz glass, and a bubble layer 12 made of quartz glass and formed outside the transparent layer 11. A ratio of an infrared transmittance of the corner portion 10c at a maximum thickness position of the corner portion 10c to an infrared transmittance of the side wall portion 10a is 0.3 or more and 0.99 or less, and an absolute value of a rate of change in infrared transmittance in a height direction along a wall surface of the crucible from a center of the bottom portion 10b toward an upper end of the side wall portion 10a is 3%/cm or less.

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.

Provided is a Li.sub.2O—Al.sub.2O.sub.3—SiO.sub.2-based crystallized glass that has a high permeability to light in an ultraviolet to infrared range and is less susceptible to breakage. A Li.sub.2O—Al.sub.2O.sub.3—SiO.sub.2-based crystallized glass contains, in terms of % by mass, 40 to 90% SiO.sub.2, 1 to 10% Li.sub.2O, 5 to 30% Al.sub.2O.sub.3, 0 to 20% SnO.sub.2, over 0 to 20% ZrO.sub.2, 0 to below 2% TiO.sub.2, 0 to 10% MgO, and 0 to 10% P.sub.2O.sub.5 and includes a β-spodumene solid solution precipitated as a main crystalline phase.

A low infrared absorbing lithium glass includes FeO in the range of 0.0005-0.015 wt %, more preferably 0.001-0.010 wt %, and a redox ratio in the range of 0.005-0.15, more preferably in the range of 0.005-010. The glass can be chemically tempered and used to provide a ballistic viewing cover for night vision goggles or scope. A method is provided to change a glass making process from making a high infrared absorbing lithium glass having FeO in the range of 0.02 to 0.04 wt % and a redox ratio in the range of 0.2 to 0.4 to the low infrared absorbing lithium glass by adding additional oxidizers to the batch materials. A second method is provided to change a glass making process from making a low infrared absorbing lithium glass to the high infrared absorbing lithium glass by adding additional reducers to the batch material. In one embodiment of the invention the oxidizer is CeO.sub.2. An embodiment of the invention covers a glass made according to the method.

A low infrared absorbing lithium glass includes FeO in the range of 0.0005-0.015 wt %, more preferably 0.001-0.010 wt %, and a redox ratio in the range of 0.005-0.15, more preferably in the range of 0.005-010. The glass can be chemically tempered and used to provide a ballistic viewing cover for night vision goggles or scope. A method is provided to change a glass making process from making a high infrared absorbing lithium glass having FeO in the range of 0.02 to 0.04 wt % and a redox ratio in the range of 0.2 to 0.4 to the low infrared absorbing lithium glass by adding additional oxidizers to the batch materials. A second method is provided to change a glass making process from making a low infrared absorbing lithium glass to the high infrared absorbing lithium glass by adding additional reducers to the batch material. In one embodiment of the invention the oxidizer is CeO.sub.2. An embodiment of the invention covers a glass made according to the method.

Provided is a small-diameter chalcogenide glass material having excellent weather resistance and mechanical strength and being suitable as an optical element for an infrared sensor. The chalcogenide glass material has an unpolished side surface, a pillar shape with a diameter of 15 mm or less, and a composition of, in terms of % by mole, 40 to 90% S+Se+Te and an inside of the glass material is free of stria with a length of 500 μm or more.

A transparent coloured lithium aluminium silicate glass ceramic and method of producing are provided. The glass ceramic has a brightness Y of 0.1% to 80% at thickness 4 mm. The glass ceramic has a D65 standard illuminant light, after passing through the glass ceramic with thickness 4 mm, with a colour locus in a white region W1 determined by coordinates in a chromaticity diagram CIExyY-2°: TABLE-US-00001 White region W1 x y 0.27 0.21 0.22 0.25 0.32 0.37 0.45 0.45 0.47 0.34 0.36 0.29.

A transparent coloured lithium aluminium silicate glass ceramic and method of producing are provided. The glass ceramic has a brightness Y of 0.1% to 80% at thickness 4 mm. The glass ceramic has a D65 standard illuminant light, after passing through the glass ceramic with thickness 4 mm, with a colour locus in a white region W1 determined by coordinates in a chromaticity diagram CIExyY-2°: TABLE-US-00001 White region W1 x y 0.27 0.21 0.22 0.25 0.32 0.37 0.45 0.45 0.47 0.34 0.36 0.29.

Provided is a method for manufacturing an infrared-transmissive lens having an excellent surface quality. A method for manufacturing an infrared-transmissive lens includes firing a preform of a chalcogenide glass in an inert gas atmosphere to obtain a fired body and then subjecting the fired body to hot press molding.