A glass including at least one type of oxide selected from TiO.sub.2, Nb.sub.2O.sub.5, WO.sub.3, and Bi.sub.2O.sub.3 as a glass component therefor, having a total TiO.sub.2, Nb.sub.2O.sub.5, WO.sub.3, and Bi.sub.2O.sub.3 content of at least 20 mol %, and having a OH value indicated in formula (1) that fulfills the relationship indicated in formula (2).
OH=[ln(B/A)]/t(1);
OH0.4891ln(1/HR)+2.48(2).

A process deciding method in a method of manufacturing an optical element by heating and press-molding an optical material to mold the optical element using a molding die on which a release film is formed, includes a basicity degree identifying process in which a degree of basicity of the optical material is identified; and a removing process determining process of determining whether to perform one or both of first removing process in which an oxidizing substance is removed and a second removing process in which a basic substance is removed from at least one of a surface of the optical material and a surface of the release film by comparing the degree of basicity of the optical material identified in the basicity degree identifying process with a predetermined reference value, before press-molding the optical material.

[Problem] The transmittance of glass can be dramatically improved as a result of this glass production method. In addition, the amount of rare metal, such as platinum, that melts into glass can be greatly reduced. [Solution] A glass production method whereby the water content in molten glass is increased, in a melting step (i) in which a glass raw material including at least one type of component among TiO.sub.2, Nb.sub.2O.sub.5, WO.sub.3, and Bi.sub.2O.sub.3 is heated inside a melting container and melted, and a molten glass is obtained.

Provided is a method of molding an optical element. The method includes: inserting a neck portion provided in each of an upper mold and a lower mold into a hole portion provided in a side surface mold; replacing an atmosphere in the hole portion of the side surface mold with an inert gas through a groove communicating between either an upper end surface or a lower end surface of the side surface mold and the hole portion of the side surface mold; heating a molding material disposed in the hole portion of the side surface mold; and bringing the upper mold and the side surface mold, and the lower mold relatively close to each other to press molding the molding material to obtain an optical element.

The disclosure relates to a method for producing an optical element (202), wherein a blank of transparent material is heated and/or provided and, after heating and/or after being provided between a first mold (UF) and at least one second mold (OF), is press molded, for example on both sides, to form the optical element (202) and is then exposed to a treatment atmosphere.