Patination of metal is an artificial aging process or the application of an unusual color with a heterogeneous structure. Patination is carried out using special paints, chemical substances, or chemical reactions. Patina (from Italian "patina") is a film of various shades (ranging from green to brown) that forms on the surface of products made of copper, bronze, and brass as a result of metal corrosion due to exposure to the natural environment or as a result of patination, which involves heating or treatment with oxidizers. The concept of patination as a "layer of antiquity" was first recognized by artists in Ancient Rome. The German Iron Cross is an ancient military award established in 1813 by King Frederick William III of Prussia as a symbol of bravery and dignity. There is nothing political or negative about this symbol — it is not associated with any ideologies and carries exclusively historical and cult significance. Bikers started using the Iron Cross after World War II. Many American veterans who returned home sought freedom and unity on the open spaces of the roads, forming the first motorcycle clubs. The Iron Cross was chosen by them as a sign of protest against the conventions of society and as a symbol of independence. The use of this symbol has become a kind of reference to the military past and an expression of the rebellious spirit that unites the brotherhood of bikers. Today, this symbol for bikers means courage, brutality, loyalty to the road — and does not carry anything political or negative.