A highly concentrated source of boric oxide for glazes. Anhydrous borax is made by burning or fusing hydrated borax. It thus contains little or no water of crystallization and does not rehydrate under normal storage conditions. Anhydrous borax is water soluble, but considerably less so than raw borax (in aqueous solution it can provide slow release of boron).
This material does not puff or swell during melting (minimizing loss of powder in kilns with strong drafts), and melts easier (the swelling in other forms can create a porous state with an insulation factor that slows melting). Anhydrous borax is an excellent glass former, it does not puff or swell during melting thus fewer production problems result.
This material is used as a source of B2O3 in the manufacture of many different types of borosilicate glass, including heat and chemical resistant glasses, illumination glasses, optical lenses, medical and cosmetic containers, hollow microspheres and glass beads. It has a higher bulk density and melts more rapidly than raw forms of borax. It also provides a source of sodium.