This means that with a fixed gas chemistry the resulting surface metallurgy is fixed. The process of pulsed plasma nitriding relies on the ionization of nitrogen and hydrogen (particularly the nitrogen). The hydrogen has a twofold purpose. It is a dilutant gas as well as a cleaning (reducing) gas. Thus, the ratio of nitrogen to hydrogen can be varied according to the steel being treated and the immediate surface metallurgy requirements necessary for the specific application. Consequently, gas ratio variation equals variable surface metallurgy.