FAQ: Taking the mystery out of patina, rust & 'stainless' steel

30th Mar 2015

Here at KnivesShipFree.com, among the questions we’re asked most often are, “Why did the blade of my new knife turn gray the first time I used it?” and “Why is there rust on my stainless-steel knife?”

For the sake of simplicity, we can say that knife blades are made from either stainless steel or carbon steel. The fundamental difference between the two is in the amount of chromium added to the iron-based material -- a steel with at least 13% chromium content generally is considered "stainless."

Carbon steel -- like the 1095 used by Great Eastern Cutlery and the A2 used by Bark River Knives, to name two -- naturally is more prone to something called “oxidation,” the most damaging form of which is rust. Another type of oxidation, the kind that darkens a shiny new knife blade, commonly is called “patina” -- and it’s actually a good thing.

Before the advent of mass-produced stainless-steel knives, virtually all blades were carbon steel. When a knife developed a patina of gray or even black, the change in color simply was an indication of use. Some still consider patina a sign of character – both of the tool and the owner.

Most important, patina forms a sort of protective barrier to more sinister oxidation. It tends to fill-in microscopic imperfections in the surface of the steel, making it more difficult for rust to take hold. In fact, many savvy (and impatient) knife owners intentionally “force” a patina on their knives by cutting onions, potatoes, pineapples or strawberries.

Of course, it’s possible to remove patina with fine metal polish. The question is, why would you want to?

With that understanding, then, let’s talk stainless. One of the most common misconceptions among knife owners is that “stainless steel” means “rustproof steel.”

It doesn’t -- rust-resistant, maybe, but not rustproof. Although nasty orange oxidation has to work harder to develop on stainless steel, it’ll show up eventually if a knife isn’t cared for properly.

Allowing food residue, blood or moisture to sit on the blade is just begging for rust (and permanent damage), so the simple practice of cleaning a knife after each use -- and checking that it’s dry before sheathing it -- is common-sense maintenance. It’s also a good idea to wipe it down regularly with a light oil, but make sure that it’s a non-detergent oil and, if you use your knife to cut food, that it’s non-toxic.

Carbon steel or stainless, no matter what you paid, your knife is an investment. You don’t have to pamper it to make it last a lifetime -- all it takes is an ounce of prevention.