This instructable covers how to etch a knife blade.
Modern knifes are often made from stainless steel and other corrosion resistant materials. To encourage etching electricity can be used. Don't worry, 9V is enough!
Etching is different from engraving. Engraving is usually scratching fine lines into the surface of the material, whereas etching chemically removes material, possibly until a hole is created! Etching can often go deeper than engraving.
I should mention that I got the information on how to do this from this site , it came up from a google result and gives you the basic info on how to do it. I've added pictures of my experience to help you along the way
Step 1: Materials
-nail varnish (paint may do instead),
-acetone (nail varnish removed or other cleaning solvent might do),
-a 9V battery,
-a scribe or pin,
-the object to be engraved,
-a dish to do it in.
Step 2: Coat the blade
Step 3: While that's drying...
I just added a bit of salt, don't think I got anywhere near saturating the water, just enough to make it salty - a good electrolyte.