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Anhydrous Borax

Alternate Names: Calcined Borax, Dehydrated Borax, Pyrobor

Oxide Analysis Formula
Na2O 30.82% 1.00
B2O3 69.19% 2.00
Oxide Weight 201.19
Formula Weight 201.19


A highly concentrated source of boric oxide for glazes (which also brings Na2O, it is sodium borate). Anhydrous borax is made by fusing hydrated borax into a glass and regrinding it. It thus contains little or no water of crystallization. The powder does not rehydrate under normal dry storage conditions. It is somewhat water soluble, but considerably less so than raw borax (in aqueous solution it can thus 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 since its boron content is so high (and the accompanying sodium is a strong flux).

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.

Related Information


Dehybor Data Sheet
Minerals Borate Minerals
Materials Boric Acid
Materials Borax Pentahydrate
Materials Borax Decahydrate
Materials Boric Oxide
Materials Disodium Octaborate Tetrahydrate
Hazards Boron Compounds and Their Toxicity
Typecodes Generic Material
Generic materials are those with no brand name. Normally they are theoretical, the chemistry portrays what a specimen would be if it had no contamination. Generic materials are helpful in educational situations where students need to study material theory (later they graduate to dealing with real world materials). They are also helpful where the chemistry of an actual material is not known. Often the accuracy of calculations is sufficient using generic materials.
Typecodes Flux Source
Materials that source Na2O, K2O, Li2O, CaO, MgO and other fluxes but are not feldspars or frits. Remember that materials can be flux sources but also perform many other roles. For example, talc is a flux in high temperature glazes, but a matting agent in low temperatures ones. It can also be a flux, a filler and an expansion increaser in bodies.


Frit Softening Point742C
Density (Specific Gravity)2.36

By Tony Hansen

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