Hey Kengore,
The easiest way that I know of to make a glossy blank matte is to use a grey (very fine) 3M scotchbrite pad. If you carefully rub the blank with one of these pads, you can remove the gloss and not harm the actual graphite fibers. I have also used the finest steel wool that you can find (OOOO in my case) and that also worked very well.
All it takes is a bit of patience and some elbow grease and you can get a very nice looking matte blank.
HTH,
Lou