I've used yellow mustard quite a bit on 01. It works very nicely. I like to leave it on over night(6-8 hours). I've made waves, tiger stripes, squiggles and written stuff on the blade.
I spread it on the blade with my fingers. Once it is coated, I use my finger to make paterns in the mustard, exposing the steel. It's where the mustard is very thin that it seems to get the darkest. Let it set for 6-8 hours, then I wash it off in warm water with gentle scrubbing with a very fine steel wool.
My kids look at me funny when I coat the blades and leave them laying around.
Polish up a scrap and try it. Have fun.
Oh yeah, don't lick the mustard off the blade.....
Ric