Inert gas, which is third place in quantity of all existing gases on earth. Almost 1% of the global atmosphere is Argon. Does not react with any other chemical element.

Argon is a frequently used process gas for Plasma treatment which does not chemically react with any substrate but which enables cleaning and etching (ion etching IE) by physical effects (micro sandblasting) and which can generate radicals on organic polymers.

Argon Plasma
Typical colour of an Argon plasma