in the how to's neil charity uses battery acid to etch his blade and ends up with a spectacular looking blade how does he do this or am i misseing something thx

Logan,
Neil's blade is damascus, and the patterns of the different steels forged together can be brought out by etching with dilute sulphuric acid, as he mentions, muriatic acid, ferric chloride, etc.
Ferric chloride is probably the safest - no noxious fumes, and is available from Radio Shack.