As mentioned above, you may use ferric chloride, but don't leave it in the solution very long. It can make a real mess of your blade. The warm apple cider vinegar with 5% acidity renders a more controlable etch. Be aware that when you use either of these, your first impression will be that you've ruined the blade. The blade will begin to turn black all over. What you do after the etch will depend on the look you want. If you just slightly etch the surface, then the top (softer) portion above the transition line will be dark, and the harder edge portion will be satiny matte gray.
I like to use another method which I learned from Jerry Fisk a few years ago. It causes just the transition line to be dark. The softer steel will still be satiny, just not black. This is a LOT of work and very time consuming, but leaves a look that I like. Here is a picture of a blade I did using the method which will be explained below.
<img src="http://www.shreve.net/~primos/dphunt.jpg" width=348 height=184 border=0 alt="Drop Point Hunter">
The blade was hand rubbed to a 400 grit finish, then slightly etched in warm apple cider vinegar (5% acidity). After etching, the blade was thoroughly washed and wiped down with paper towels to get a lot of the dark crap off. Next I coated the blade with a light film of automotive rubbing compound (the white stuff)and a bit of water, and rubbed it with a piece of leather glued to a tongue depressor -- the big Popcicle stick that a doctor uses. What is left is the dark transition line which is sometimes referred to as a temper line or hardening line. This takes a long time, but I like the way it looks. You will have to add compound and a sprinkle of water from time to time. The stuff gets thick and gunky.
You will probably want to experiment with this some before attempting it on a good blade.
[This message has been edited by primos (edited 03-20-2000).]
