Reflex gauge glass is used to read the medium level in the boiler or other tanks. The one side of the glass which is exposed to the medium has a prismatic surface and another side is smooth. The medium level inside the level gauge is indicated as the result of the light refraction principle, since the liquid filled area completely absorbs the rays of light and appears dark, whereas the rays of light are totally reflected in the gas/air filled area which appears bright. Reflex gauge glass is made from high borosilicte glass. It has many advantages, such as cheap, low maintenance cost, easy level reading and excellent high temperature & pressure resistance. Its working pressure can be up to 4 MPa and working temperature can be up to 430 C. The edge can be polished or frosted.