Another technique for darkening screws and other metal hardware is to apply an oil, such as peanut or linseed oil, and use a torch to heat them until it sort of cooks on.    I suppose you could try using gun black too.

 When I need to cut a slot in a screw, I usually use a Dremel with a cutoff disk but even that might be too thick for a #2 screw.   

--Nathan, TX. Hire the lazy man. He may not do as much work but that's because he will find a better way.