I use aqua fortis, it is traditional and really brings out all the beauty of the wood. I also get to play with dangerous chemicals and fire...
Good directions and fascinating discussion here.
Basic directions:
I don't mix up my own, but buy it from
http://www.trackofthewolf.com/index.aspx. I first sand the wood to 500 grit, then whisker the wood until the fibers stay down (this is essential! to whisker, use a moist sponge and wipe the wood... when it drys, little 'whiskers' will stand up... take them down with 0000 steel wool... repeat until no whiskers pop up). Then, wearing gloves, I sponge a light coat of aqua fortis on the wood. I quickly light my gas forge (any heat source will do, a heat -gun, oven-eye, etc...), then move the handle in front of the port. As soon as the wood blushes, I move to another spot until the entire surface is colored. Try to avoid charring the wood. Then I wipe it down with linseed oil, and it is done.