This is an easy and cheap way to etch steel, like knife blades, using things you probably already have at home. This is what you need:
Two 20 centimeter bits of electric wire with crocodile clips in the ends.
A 9 volt battery.
A razor blade.
Something made of metal that you want to etch.
And this is how you do:
Apply tape to the steel where you want the etching to be.
Cut out the pattern you want to etch in the tape.
Attach one of the wires to the plus terminal of the battery and the other end to the metal using the crocodile clips.
Soak a cue tip in the salt water.
Attach one end of the other wire to the battery minus terminal and the other end to the soaked cotton of the cue tip.
Hold the soaked cue tip end to the visible metal pattern you created in step 2. This starts the etching.
Move the cue tip around the pattern to etch all of it. You probably need several cue tips depending on the size of the pattern.
Remove the tape to reveal the pattern when you are done. Try on a piece of scrap metal before you do it on something valuable.