Optical glass

An optical glass, comprising:

• a refractive index (nd) of no less than 1.75 and an Abbe number (vd) of no less than 10 as optical constants,
• wherein a Bi2O3 content is no less than 51.310% by weight to no more than 80.643% by weight, a content of B2O3 is from no less than 7.530% by weight to no more than 30% by weight, a content of SiO2 is no more than 5.861% by weight, a total content of Ln2O3+RO+Rn2O is from no less than 0.5% by weight to no more than 50% by weight, a content of ZnO is no more than 10% by weight, in which R represents one or more elements selected from the group consisting of Zn, Ba, Sr, Ca, and Mg, in which Rn represents one or more elements selected from the group consisting of Li, Na, K and Cs, and in which Ln represents one or more elements selected from the group consisting of La, Gd, Y, Ce, Eu, Dy, Yb and Lu,
• wherein the optical glass has at least one of the properties of being substantially free from opacification and/or being substantially devitrified within the glass body under the conditions of the following reheating test (a), and
• wherein, a test piece of 15 mm by 15 mm by 30 mm is reheated, such that the test piece is heated from room temperature to a temperature of 80 degrees C. higher than its transition temperature (Tg) for a period of 150 minutes, maintained for 30 minutes at the temperature of 80 degrees C. higher than the glass transition temperature (Tg) of the optical glass, allowed to cool to an ambient temperature, and finally observed visually after polishing the opposing two sides of the test piece to a thickness of 10 mm.