Anløper

Anløper is a Norwegian term that can refer to several related concepts, primarily concerning discoloration or staining on surfaces, often metal.

In the context of metallurgy, anløper refers to the visible oxide layer that forms on steel when it is heated in the presence of oxygen. This layer, often called temper colors or heat tint, appears as a spectrum of iridescent colors, ranging from straw yellow to blue, depending on the temperature reached. These colors are a result of interference of light waves reflecting off the oxide layer and the underlying metal surface. Anløper is a direct indicator of heat treatment processes and can be indicative of stress or changes in the material's properties.

More broadly, anløper can also describe any kind of surface stain or discoloration, especially on metals like silver or copper, caused by chemical reactions with the environment. This can include tarnish, which is a form of anløper caused by sulfides. Therefore, in common usage, anløper is often synonymous with tarnishing or oxidation that affects the aesthetic appearance of an object. The term is also sometimes used in a figurative sense to describe a blemish or imperfection.