Hey Slice, DC etches, AC blackens. GSOM put out a good tutorial that I always refer back to when I do it.
http://www.bladeforums.com/forums/s...cal-etching-on-a-BK12?p=13234190#post13234190
http://www.bladeforums.com/forums/s...cal-etching-on-a-BK12?p=13234190#post13234190