[hammerdownnow]

Vinagar patena (ageing),, is like a cross between what Don Cowles does with rubbing the blade with a slice of lemon, or like etching with Fc. It is all etching i guess. The vinagar and lemon are just slower than the Ferric cloride. Ray Richards does it with mustard. When you cut acidic food with your high carbon blade it it tends to leave dark streaks that look uneven. Light etching with citric or whatever kind of acid vinagar is, coats the blade evenly with a fast black rust that makes it hard for the red rust to stick to. IMO, the eveness of a light controled patena is preferrable to the waiting envolved in natural patena, which is inevidable unless you buff it after every use. I just know this from experence with my own collection of high carbon kitchen knives.