ABSTRACT
In one method, naturally occurring quartz is purified to varying degrees by preselection of clean crystalline material, fragmented to a fine powder, and fused to bulk glass. The fusion is performed by electric melting in a refractory crucible or container under vacuum, an inert atmosphere, or a hydrogen atmosphere. This produces a type of vitreous silica designated as type I. If the same raw material is fused using an oxyhydrogen torch or an isothermal plasma torch, then the resultant vitreous silica is designated type II. The principal differences between these are the lower hydroxyl content and different impurities of type I.
