Liquid level indicators are equipped with boron silicate glass, hardened by an accurately controlled heat treatment process. These level indicators are used to display the level of ammonia gas in the system. The liquid level indicators are installed with stop valves equipped with handwheels. The liquid chamber is a one piece metal body covered by glass. The light striking the glass in the liquid portion is absorbed by the liquid whereas the light striking the glass in the vapour portion is reflected, making the liquid appear black.