Boric Acid

Boric acid is boron and water, with no sodium or potassium. Boron lowers a glaze's melting point without pushing up its thermal expansion, and an alkali arriving with the boron would push that expansion straight back up. So where a recipe cannot take the soda that comes with borax, this is the boron source to use. It dissolves in water, though, and dissolved boron moves with the water. As a glazed piece dries, the water soaks into the bisque and carries the boron with it, so the glaze fires under melted and the clay beneath it over fluxed. That is why boron usually reaches a glaze as a frit, and boric acid is one of the materials frit makers melt to get there. In a studio it is used for making your own frit or your own low fire glaze base. For ordinary glaze work a boron frit is the more dependable route.