This invention relates to the preparation of glass, and is particularly concerned with the preparation of high purity glasses such as low optical loss glasses required for optical fiber manufacture and those required as host glasses for laser manufacture.
High purity oxide glasses are normally prepared by melting together extremely pure oxides or carbonates of the necessary elements to give the glass. Many of these oxides and carbonates are difficult to prepare with adequate purity by conventional precipitation methods, and as a result are costly. The elements of those of the oxides that are oxides of metallic or semiconductive elements are however relatively easy to purify by zone refining. We disclose that glass of high purity can be made using these zone refined elements as starting materials. The zone refined materials may be oxidized separately but in many instances it is preferable to form a single melt of all the zone refined constituents before oxidation.