A strengthened glass or glass ceramic sheet has a first major surface, a second major surface opposite the first major surface, an interior region between the first and second surfaces, an outer edge surface extending between the first and second major surfaces, and a thickness between the first major surface and the second major surfaces, wherein the sheet comprises a glass or glass ceramic and is thermally strengthened and wherein the first major surface has a roughness of more than 0.1 nm Ra and less than 500 nm Ra over an area of 10 m10 m and wherein PP<0.05.Math.(LL), where LL is the maximum differential optical retardation with a slow axis closer to perpendicular than to parallel to the outer edge of the sheet, measured through the sheet through the first and second major surfaces of the sheet at a measurement location on the first surface of the sheet, as the measurement location moves inward from a point at the outer edge of the sheet, to a point three times the thickness from the outer edge, and where PP is the maximum differential optical retardation with a slow axis closer to parallel than to perpendicular to the outer edge of the sheet, measured through the sheet through the first and second major surfaces of the sheet, at the measurement location as the measurement location moves inward from the point at the outer edge of the sheet, to a point three times the thickness from the outer edge.

A strengthened glass or glass ceramic sheet has a first major surface, a second major surface opposite the first major surface, an interior region between the first and second surfaces, an outer edge surface extending between the first and second major surfaces, and a thickness between the first major surface and the second major surfaces, wherein the sheet comprises a glass or glass ceramic and is thermally strengthened and wherein the first major surface has a roughness of more than 0.1 nm Ra and less than 500 nm Ra over an area of 10 m10 m and wherein PP<0.05.Math.(LL), where LL is the maximum differential optical retardation with a slow axis closer to perpendicular than to parallel to the outer edge of the sheet, measured through the sheet through the first and second major surfaces of the sheet at a measurement location on the first surface of the sheet, as the measurement location moves inward from a point at the outer edge of the sheet, to a point three times the thickness from the outer edge, and where PP is the maximum differential optical retardation with a slow axis closer to parallel than to perpendicular to the outer edge of the sheet, measured through the sheet through the first and second major surfaces of the sheet, at the measurement location as the measurement location moves inward from the point at the outer edge of the sheet, to a point three times the thickness from the outer edge.

A glass sheet thermally strengthened such that at the first major surface is under compressive stress; the sheet having an a characteristic 2D autocorrelation matrix c(x,y) given by c(x,y)=F.sup.1(F(g).Math.F(g)) where F is a 2D Fourier transform and represents a complex conjugate operation and g is a high pass filtered data array given by g(x,y)=F.sup.1(F(f(1F(h)) where h is a spatial 2D low pass filter array and f is a square data array of Shear 0 and Shear 45 data, taken over an area away from any birefringence edge effects on the sheet, wherein an autocorrelation peak maximum width of the matrix c(x,y) at 40% of peak height, for the c(x,y) matrices from both the Shear 0 and Shear 45 data, is between 1 and 5 mm.

A glass sheet thermally strengthened such that at the first major surface is under compressive stress; the sheet having an a characteristic 2D autocorrelation matrix c(x,y) given by c(x,y)=F.sup.1(F(g).Math.F(g)) where F is a 2D Fourier transform and represents a complex conjugate operation and g is a high pass filtered data array given by g(x,y)=F.sup.1(F(f(1F(h)) where h is a spatial 2D low pass filter array and f is a square data array of Shear 0 and Shear 45 data, taken over an area away from any birefringence edge effects on the sheet, wherein an autocorrelation peak maximum width of the matrix c(x,y) at 40% of peak height, for the c(x,y) matrices from both the Shear 0 and Shear 45 data, is between 1 and 5 mm.

A strengthened glass or glass ceramic sheet has a roughness of greater than 0.05 nm Ra and less than 0.08 nm Ra over an area of 10 m10 m and has the property that, excluding areas within three sheet thicknesses of the outer edge surface of the sheet, the slope of a measured value of a thermally affected property of glass over distance along the first major surface of the sheet is higher bordering one or more lower-cooling-rate-effect-exhibiting areas on the first surface of the sheet than elsewhere on the first surface of the sheet, and at least one of said one or more areas has a shortest linear dimension, in a direction parallel to the first major surface, of less than 100000 m.

A strengthened glass or glass ceramic sheet has a roughness of greater than 0.05 nm Ra and less than 0.08 nm Ra over an area of 10 m10 m and has the property that, excluding areas within three sheet thicknesses of the outer edge surface of the sheet, the slope of a measured value of a thermally affected property of glass over distance along the first major surface of the sheet is higher bordering one or more lower-cooling-rate-effect-exhibiting areas on the first surface of the sheet than elsewhere on the first surface of the sheet, and at least one of said one or more areas has a shortest linear dimension, in a direction parallel to the first major surface, of less than 100000 m.

A strengthened glass or glass-ceramic sheet or article as well as processes and systems for making the strengthened glass or glass-ceramic sheet or article is provided. The process comprises cooling the glass sheet by non-contact thermal conduction for sufficiently long to fix a surface compression and central tension of the sheet. The process results in thermally strengthened glass sheets.

A strengthened glass or glass-ceramic sheet or article as well as processes and systems for making the strengthened glass or glass-ceramic sheet or article is provided. The process comprises cooling the glass sheet by non-contact thermal conduction for sufficiently long to fix a surface compression and central tension of the sheet. The process results in thermally strengthened glass sheets.

A strengthened cover glass or glass-ceramic sheet or article as well as processes and systems for making the strengthened glass or glass-ceramic sheet or article is provided for use in consumer electronic devices. The process comprises cooling the cover glass sheet by non-contact thermal conduction for sufficiently long to fix a surface compression and central tension of the sheet. The process results in thermally strengthened cover glass sheets for use in or on consumer electronic products.

A strengthened cover glass or glass-ceramic sheet or article as well as processes and systems for making the strengthened glass or glass-ceramic sheet or article is provided for use in consumer electronic devices. The process comprises cooling the cover glass sheet by non-contact thermal conduction for sufficiently long to fix a surface compression and central tension of the sheet. The process results in thermally strengthened cover glass sheets for use in or on consumer electronic products.