Typically, a varnishing unit in a printing machine is constructed as a separate unit disposed after the printing units and before the delivery unit of the machine. In many printing machines of this kind perfecting is possible only by turning the sheet over; for example, German Auslegeschrift No. 2,608,661 discloses a printing machine of this type. But in such printing machines the perfecting process subjects the previously applied varnish to pressure which destroys the smooth sheet surface produced by varnishing. Other printing machines which include varnishing as a final operation have no provision for perfecting; therefore, varnish can be applied without difficulty. Examples of such printing machines are disclosed in German Patentschrift Nos. 2,020,584 and 2,345,183.