Borax and sodium borate are the same material, and in ceramics boron is the flux that makes low-temperature glazes possible. It melts glass at temperatures nothing else reaches usefully, which is why almost every earthenware and low-fire glaze depends on it in one form or another.
What boron does
Boron behaves like a flux and like a glass former at once, so it lowers the melting point of a glaze sharply while still contributing to the glass itself. That combination is what makes bright, glossy, well-melted glazes possible at earthenware temperature, where silica alone would not melt at all. Almost all commercial low-fire glazes are boron glazes.
Why most recipes use a frit instead
Raw borax is soluble in water, so in a glaze bucket it dissolves, migrates into the bisque and concentrates at the surface as the glaze dries. The standard answer is a borosilicate frit: the boron is pre-melted into an insoluble glass, so it stays where it is put. Most modern recipes therefore call for a frit and raw borax appears mainly in older ones.
Where raw borax is still used
In some raku and low-fire glazes where the solubility matters less, in fritting your own materials, and in traditional recipes reproduced as written. If you are following an old recipe that calls for raw borax and getting inconsistent results, solubility is the first thing to suspect and a frit substitution is the usual modernisation.
Handling
Borax is a fine powder and the usual precautions apply: weigh in a ventilated space with a fitted respirator, wet-clean afterwards. It is also worth keeping dry in storage, because it cakes badly with absorbed moisture and a caked bag weighs differently from a fresh one.
Questions people ask about borax powder uk
Is borax the same as sodium borate?
Yes. Sodium borate is the chemical name and borax the common one for the same material.
Why is a frit better than raw borax?
The boron in a frit is already melted into an insoluble glass, so it does not dissolve in the glaze bucket and migrate as the glaze dries.
What does boron do that other fluxes cannot?
It melts glass at low temperatures while contributing to the glass itself, which is what makes bright, well-melted earthenware glazes possible.