If I were considering doing this, I'd go audit the Mandalorian boards and builds. Those guys have done it for years. There's no reason to re-invent the wheel when they've done every kind of experiment and combination possible. I know one recurring comment I've seen about it being 'messy' is that if you truly grind it in to your part, then it doesn't come off easily, and conversely if it comes of easily or 'messily' then you're just applying it to the top and its just laying there not really ground into the gloss black below. I get the impression they're aiming to practically embed the graphite into the gloss black and not just ride on top.
Oh - another video I saw on YouTube was someone graphiting a sword - so that might be another search path for you to see other people's techniques and results.