This is just copied from my post in the DIY Walking Axe thread..assuming it is Ti, try putting some tape on the side you want to mark - leave small slits (like you wanted to paint the lines) where you want the marks, and follow these steps. The tape should be thick enough to stop the voltage from changing the color of the material.
Here is my setup my set-up:
Four 9 volt batteries
Wires with aligator clips
small piece of aluminum foil (tinfoil)
1 can of diet pepsi
Wire the batteries in series (not parallel).
Wrap a ball of aluminum foil in a piece of paper towel.
Attach the negative wire to the titanium part.
Attach the positive wire to the aluminum foil/paper ball.
Dip the ball into the pepsi.
Touch the titanium part with the aluminum/paper ball.
It will change color immediately, but will require you to hold it there for several seconds in order to reach the final color.
If you are not getting results, make sure you have a closed circuit. I usually pour a little pepsi all over the part and clips to ensure a good connection.
Keep an eye on the batteries, they get dang hot. I don't want someone telling me they blew up on them.
Disclaimer: Following this procedure may lead to death. Blunt enough?