Sort of along the same subject...well maybe not...I just starting laying Prismacolor Premier Fine Line Markers (black mostly) into tight detail pieces and then using a brush to feather the ink into harder to reach corners. If it's down too dark you can wipe away small amounts with a cotton swab or wipe it off altogether if the swab is wet enough. I've been doing this on top of acrylics so I can't advise over other mediums. The effect gives a real nice shadow, defines corners, and can add a grimy look to landing gear hydraulics. Used with some of the other colors in the set and you can produce grease stains and other effects. This dry marker/pen technique offers 100% control of the ink. But as good as this is I will still use a pastel wash for the truly deep down bowels of Hades areas.

That's my 2 cents...and I'm stickin' with it.