Weight loss at the metal surface due to oxygen exposure. Reaction products are usually generated at the metal surface when subjected to high temperatures.

For example, at above 575°C, a scale layer is formed on ferrous surfaces which consists of wüstite (FeO), changing into hematite (Fe2O3) on the outside via an intermediate layer of magnetite (Fe3O4, mill scale).

Therefore, the composition of the scale layer is clearly temperature-dependent (see Scaling).