Engine turning refers to a fine geometric pattern that can be inscribed onto metal as a finish. Aluminium is often the metal chosen but any metal can be finely machined to produce intricate repetitive patterns that offer reflective interest and fine detail.
Perhaps the most recognizable example of engine turning is the engine cowling (nose) of Charles Lindbergh's aircraft, the Spirit of St. Louis. In the 1920s and '30s, automobile parts such as valve covers, which are right on top of the engine, were also engine-turned. Similarly, dashboards or the instrument panel of the same were often engine-turned. Customizers also would decorate their vehicles with engine-turned panels similarly. Recently, one firm engine-turns the faces of its automobile instruments for customizers who don't want to have to turn a panel themselves.
Engravings produced by engine turning are often incorporated into the design of bank notes and other high value documents to make production of forged copies difficult. The resulting graphics are called guillochés.