Naw, I understood, just making a wisecrack. Poorly, though, I guess! Sorry about that. Acid patinas are corrosion, or rust, as Jason pointed out himself (he also points out that a few of the iron oxides are mildly passivating, which is particularly important to cooks).
Black or grey rust will hold some oil and can keep your steel from developing red rust when exposed to moisture. But it doesn't strengthen the blade in any meaningful way, and isn't a substitute for keeping the blade clean between uses. It mostly just makes it prettier, bringing out any grain in the metal, and prevents mildly acidic foods from reacting with the raw iron and generating "off" tastes.
My blades and other metal accoutrements get patinated with use pretty quickly; for one thing, my sweat seems to be more corrosive than that of other people, for another, blood does the job up a treat (I'm a meat-eater as well as a tool user and occasional smith). Most of my armor has a heavy brown patina, most of my blades have a dark grey to black patina, with mirror edges.