Disclosed herein are glass-based articles having a first surface having an edge, wherein a maximum optical retardation of the first surface is at the edge and the maximum optical retardation is less than or equal to about 40 nm and wherein the optical retardation decreases from the edge toward a central region of the first surface, the central region having a boundary defined by a distance from the edge toward a center point of the first surface, wherein the distance is ½ of the shortest distance from the edge to the center point.

A method for manufacturing an SiO.sub.2—TiO.sub.2 based glass upon a target by a direct method, includes a first process of preheating the target and a second process of growing an SiO.sub.2—TiO.sub.2 based glass ingot to a predetermined length upon the target which has been preheated, wherein the target is heated in the first process such that, in the second process, the temperature of growing surface of the glass ingot is maintained at or above a predetermined lower limit temperature.

A silica-titania glass substrate comprising: (i) a composition comprising 5 weight percent to 10 weight percent TiO.sub.2; (ii) a coefficient of thermal expansion (CTE) at 20° C. in a range from −45 ppb/K to +20 ppb/K; (iii) a crossover temperature (Tzc) in a range from 10° C. to 50° C.; (iv) a slope of CTE at 20° C. in a range from 1.20 ppb/K.sup.2 to 1.75 ppb/K.sup.2; (v) a refractive index variation of less than 140 ppm; and (vi) 600 ppm OH group concentration or greater. The substrate can have a mass of 1 kg or greater and less than 0.05 gas inclusions per cubic inch via a method comprising (i) forming the substrate from soot particles comprising SiO.sub.2 and TiO.sub.2, and (ii) subjecting the substrate to an environment having an elevated temperature and an elevated pressure for a period of time until the substrate comprises less than 0.05 gas inclusions per cubic inch.

Disclosed herein are glass-based articles having a first surface having an edge, wherein a maximum optical retardation of the first surface is at the edge and the maximum optical retardation is less than or equal to about 40 nm and wherein the optical retardation decreases from the edge toward a central region of the first surface, the central region having a boundary defined by a distance from the edge toward a center point of the first surface, wherein the distance is of the shortest distance from the edge to the center point.

Disclosed herein are glass-based articles having a first surface having an edge, wherein a maximum optical retardation of the first surface is at the edge and the maximum optical retardation is less than or equal to about 40 nm and wherein the optical retardation decreases from the edge toward a central region of the first surface, the central region having a boundary defined by a distance from the edge toward a center point of the first surface, wherein the distance is of the shortest distance from the edge to the center point.

A method of producing a multicolor glass-ceramic blank (10) for dental purposes. A glass-ceramic blank (10) is produced from at least a first material powder (18) and a second material powder (20), wherein the first material powder (18) and the second material powder (20) are different-colored and wherein at least one of first material powder (18) and second material powder (20) has nanoparticles (14) and/or glass-ceramic particles (16). The first material powder (18) and the second material powder (20) are introduced into a mold (22) in order to form at least one powder mixture aggregate (26). Additionally, the powder mixture aggregate (26) is compressed by hot pressing in order to form the glass-ceramic blank (10). A multicolor glass-ceramic blank (10) is obtainable by such a method and the multicolor glass-ceramic blank (10) is used as dental material.

Provides is low scattering silica glass suitable as a material of an optical communication fiber. Silica glass has a fictive temperature of at least 1,000 C. and a void radius of at most 0.240 nm, as measured by positron annihilation lifetime spectroscopy. A method for heat-treating silica glass is also provided, which comprises holding silica glass to be heat-treated in an atmosphere at a temperature of at least 1,200 C. and at most 2,000 C. under a pressure of at least 30 MPa, and cooling the silica glass at an average temperature-decreasing rate of at least 40 C./min during cooling within a temperature range of from 1,200 C. to 900 C. A method for heat-treating silica glass also comprises holding silica glass to be heat-treated in an atmosphere at a temperature of at least 1,200 C. and at most 2,000 C. under a pressure of at least 140 MPa, and cooling the silica glass in an atmosphere under a pressure of at least 140 MPa during cooling within a temperature range of from 1,200 C. to 900 C.

A device for manufacturing SiO.sub.2TiO.sub.2 based glass by growing a glass ingot upon a target by a direct method. The device includes the target, comprising a thermal storage portion that accumulates heat by being preheated, and a heat insulating portion that suppresses conduction of heat from the thermal storage portion in a direction opposite to the glass ingot.

Disclosed herein are glass-based articles having a first surface having an edge, wherein a maximum optical retardation of the first surface is at the edge and the maximum optical retardation is less than or equal to about 40 nm and wherein the optical retardation decreases from the edge toward a central region of the first surface, the central region having a boundary defined by a distance from the edge toward a center point of the first surface, wherein the distance is ? of the shortest distance from the edge to the center point.

A method for manufacturing an SiO.sub.2TiO.sub.2 based glass upon a target by a direct method, includes: an ingot growing step of growing an SiO.sub.2TiO.sub.2 based glass ingot having a predetermined length on the target by flame hydrolysis by feeding a silicon compound and a titanium compound into an oxyhydrogen flame, wherein the ingot growing step includes: a first step of increasing a ratio of a feed rate of the titanium compound to a feed rate of the silicon compound as the SiO.sub.2TiO.sub.2 based glass ingot grows until the ratio reaches a predetermined value; and a second step of gradually growing the SiO.sub.2TiO.sub.2 based glass ingot after the ratio has reached the predetermined value in the first stage with keeping the ratio within a predetermined range.