The matte finish is actually pretty easy. I do it all the time. The
best way I've found is to start with a polished or very near
polished surface. This is going to be done dry.
Use an expanding drum with resin belts and get some diamond paste.
It depends on what kind of finish you want which grit size paste
will be best. You also need extender which is the oil base that is
in the paste.
I sometimes use 180 grit which is pretty tricky because it cuts as
well, or 260 which also cuts or 325 or 400 or 600. You have to
decide the fineness of the finish you want. Then it takes a very
light touch and adjustment for direction of texture from the grit.
It actually helps quite a lot that the belt is broken in. This takes
time and repeated applications and distribution of the paste.
Thinking about it, I guess I'd have to say it's easy now, but it
does take some work and practice to get to that point.