Abstract: The present invention relates to a method for cleaning of a surface of at least one workpiece made out of an aluminium alloy, comprising the steps of: generating an electric arc or a plasma jet by means of a torch, applying the electric arc or the plasma jet to the surface, and moving the torch and the at least one workpiece relative to one another to clean the surface by evaporating impurities of the surface using the electric arc or plasma jet, and e.g. detecting light coming from the electric arc or plasma jet by means of an optical sensor, wherein the optical sensor generates an output signal indicative of the presence of impurities of the surface evaporated by the electric arc or by the plasma jet.