It takes some time but start with sanding the slide with 400,600,800 and 1200 grit sandpaper until you have a really smooth surface and then polish it too mirror like shine. mix around a third of a bottle of aluminium black witch ca 1l water, clean the slide with degreaser, dip it in the solution for a couple of minutes and wash it of with water, let it dry, brush of the blackish sooth with a soft brush.
re-do the dipping at least three times, at first you will get a blueish, black color and after a couple of dips it will turn to a more almost chromed surface, at this time the HW material won