An oxide surface forms on almost all metal surfaces when they are exposed to free atmosphere. It significantly impairs many subsequent machining processes, for example adhesion at soldering or bonding, as well as the electrical contact; however, it also has some benefit. Very thin oxide layers are often hard and stable and protect the pure metal underneath from further attack. For this reason, the base metal forms a very shiny metallic surface which protects it from further weathering. The base metal aluminium likewise gets good protection from the aluminium oxide layer. For surface protection reasons, surface oxide layers can be specifically applied by means of plasma treatment in oxygen plasma or air plasma. A much more frequent application, however, is the removal of oxide layers before further processing, preferably by etching in hydrogen plasma.