Systems which are affected by rouging usually show discolouring. This can range from a reddish brown to violet to light blue nuances. These discolourations are usually thin layers and may be either strongly adhesive, easily wiped off or may even have a chalky characteristic. By definition, every physico-chemical interaction between a metal and its environment which leads to a change in the metal properties and substantial impairment of the function of that metal, the environment or the technical system is described as corrosion. Rouging is therefore a specific form of corrosion.
Because the phenomenon of rouging is not yet clarified in detail, theories drawn from our own experiences and observations as well as literature sources are given here (see literature)!