I've had some success with acid etching and electro-etching on copper and brass using home printed circuit board supplies. The trick is getting the metal prepped - sounds easy, but isn't! It needs to be thoroughly degreased which usually involves the use of a pickling agent after some type of degreasing agent. You design your image in photoshop or whatever, and print it onto special clear plastic (mylar) sheet with a frosted side - frosted side takes the ink. The metal is sprayed with a UV resist, dried, and the design is taped to it - it will curl into the hollow of the blade if snipped round and taped down. It is then exposed to ultra violet light and washed - the parts of the resist covered with ink will remain soft and wash away - these parts will be etched.
You then either cover the rest of the metal you don't want to etch with the resist and expose it to UV again, or make a small dam around the design that will hold a pad moistened with acid without letting it spread elsewhere.
If you don't want to use strong acid you can use a suitable electrolyte (eg copper sulphate, 10% hrdrochloric acid, etc), suspend the blade (called the anode) in it with copper wire and connect it to a car battery (or smaller - 6v at 4 amps should do it), and suspend another piece of metal (stainless will do - called the cathode) in the electrolyte connected to the other pole of the battery.
The same process as above makes use of simple salt water as the electrolyte and is described in detail here.
Regards,
Neil.