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Borax Decahydrate

Alternate Names: Sodium TetraBorate Decahydrate, Borax 10-hydrate, 10 Mol Borax, Neobor, Borax

Oxide Analysis Formula
B2O3 36.52% 2.00
Na2O 16.26% 1.00
H2O 47.21%n/a
Oxide Weight 201.25
Formula Weight 381.23


Borax Decahydrate is the refined form of natural sodium borate. Composed of boric oxide (B2O3), sodium oxide, and water, it is a mild, alkaline salt, white and crystalline, with excellent buffering and fluxing properties. Borax Decahydrate is an important multifunctional source of B2O3 (e.g. frits), particularly for processes in which the simultaneous presence of sodium is beneficial.

Borax is available in large crystal, powder, and granular form, the latter being the most practical for ceramic use. Although the 10 molecules of water in the theoretical formula vary somewhat, they are the source of the designation "10 Mol Borax". The water content can vary with storage (it tends to lose water with time). Where precision is required, it is necessary to measure the water content just before use (the material begins to melt in its own water of crystallization at 60.8C).

Almost all American borax comes from deposits of the crystalline precipitate mineral tincal in the Mohave Desert of California (Asian borax is called Tincal).

It is soluble in water, acids, glycol and other solvents. This solubility onormally disqualifies it for use in clay bodies and glazes (since during drying it will come to the surface with the water and be concentrated there). That being said, some have observed that the granular material is not all that soluble and it is necessary to ball mill glazes containing it. Of course, the smaller particle size will increase surface area and accelerate solubility overtime.

Actually, the solubility can be used to advantage to make self-glazing products like Egyptian Paste and it can produce a hardened surface in non-fired products. In addition, the migration issue during drying can be tolerated in some circumstances, borax can be employed in a traditional ceramic slip or glaze blend as a low-cost super-flux to produce a glaze or slip for low temperatures.

Rio Tinto Borax has many technical, granular and powder grades of this material. "20 Mule Team" borax is this material. It is also produced at the Bandirma Borax Plant in Turkey.

Related Information

The amazing fluxing power of boron (in borax)

The two top clay bars contain 15% hydrous borax. At cone 06, a very low temperature, it has already melted and drained out of the bars, running down over the others as a glass.

Original Container Bag of Borax Decahydrate


Borax Decahydrate Data Sheet Etibor
Data Sheet US Borax
Materials Anhydrous Borax
A white, odorless product crystalline granular by dehydrating Borax to remove the crystal bound water.
Materials Borax Pentahydrate
Materials Boric Acid
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.
Oxides B2O3 - Boric Oxide
Oxides P2O5 - Phosphorus Pentoxide
Minerals Borate Minerals
The major borate minerals are Colemanite and Ulexite. The geology required for borates is found in v
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