The invention relates to a method for treating a steel band or steel plate provided with a metal coating with an after-treatment agent, which contains at least one polyalkylene glycol and is applied as a liquid solution to the surface of the metal coating. According to the invention, in order to achieve improved wetting and adhesion of the covering and at the same time the lowest possible coefficient of friction of the coated surface and in order to ensure good workability of the coated steel band or plate, the after-treatment agent contains a fluorescent antioxidant in addition to the polyalkylene glycol. The invention further relates to a steel band or steel plate provided with a metal coating, particularly a tin plate, which, on the surface of the metal coating, has a thin coat of an after-treatment agent which contains polyalkylene glycol and a fluorescent antioxidant.