Borax is a glass making flux used to reduce the melting temperature of glass.
It is almost colourless - grey, white, or yellowish; seldom bluish or greenish; and colourless in transmitted light.
The chemical composition of Borax is: Na2(B4O5)(OH)4 · 8H2O
It has a hardness rating of 2 – 2.5, about half that of glass at approximately 5.5.
The melting point is 878°C. At this temperature borax dissolves numerous metal oxides. In spite of this high melting temperature, it acts as a flux reducing the softening point at the surface of the glass at kiln forming temperatures.
The specific gravity of borax is approximately 1.7, considerably ligther than glass at ca.2.5.
Borax is sparingly soluble in cold water, although readily soluble in boiling water. It is insoluble in ethanol.