Did I ruin this knife?” I get this question from bashful and embarrassed customers pretty frequently. The question is almost always in regard to a deeply oxidized blade. Sometimes it’s just a few gray blotches, other times there’s a bit of rust and I’ve even seen attempts to remove the oxidation make it worse. The answer is always “not at all” accompanied by a few different points. The first is encouragement to look at patina in a new way. Most people today have had little to no interaction with high carbon knives. Almost all cheaper mass production knives are stainless steel. With the exception of hazardous chemicals, stainless blades stay shiny and don’t get any kind of patina or oxidation. High carbon steel can patina or rust. But look at it as a cool natural pattern that emerges from the use of the knife. It tells the individual story of that knife and has a charming rustic aesthetic. Having a clean and shiny high carbon knife is like showing up to the job site with brand new boots on, everyone knows you’re a green horn.
Patina is just a fancy way to say something is showing it’s age by some kind of weathering. On blades this takes the form of a build up of oxidation layers that can be black, gray, purple, orange or red. The orange and red oxidation is rust which is the corrosive version of patina. Not addressing rust will lead to surface pitting but even surface pitting will not ruin the functionality of the blade. Of course it’s not good for the knife as it is actually eating away at the surface, the chemical reaction between oxygen and iron combining causes a new compound to be formed (iron oxide) which then flakes off. Even though it’s a corrosive process, it takes years for rust to completely destroy a blade so a bit on the surface with just affect the look. The other types of oxides which turn black or gray are not accompanied by pitting and can even act as a protective layer against rust. Think of gun blueing or other patina chemicals.
Ok I’ve convinced you that it’s not technically ruined but you still want the oxidation gone. I understand, to each his own. It is actually much simpler to polish a blade up than you think. I didn’t say EASY but I did say simple. Things that you’ll need to polish a blade are various grades of sandpaper, steel wool, metal polish and a rag. The first step is to assess the depth of the patina. I start with the least invasive process then work my way into more abrasive solutions. If it is very light, then just use the polish and rag until it brightens back up. Don’t be afraid to us some elbow grease, be liberal with the polish and lay the blade against a surface so you don’t cut yourself. If you are not quite getting everything with the polish, then go a step coarser to the steel wool. Make sure to use 0000 grade steel wool which is the finest grade, if you need more than that then you might as well go to sandpaper.
If you do need to go to sandpaper, I suggest starting with the finest you have. I start with something like 1000 or 1500 grit wet dry sandpaper and wet sand with Windex or WD-40. Using a lube really helps the sandpaper carry away steel dust and last longer. You can always go down to coarser grit but I wouldn’t go coarser than 400 grit because the scratches from 150 or 220 grit can take forever to get out. Once you’ve gotten down to a level where the patina or pitting are removed, the job is just moving to progressively finer grits until you are as high as you can go, then break out the polish. I like Mothers Mag and Aluminum wheel polish from the auto parts store. While you’re at it, you can buy super fine sandpaper from there too.
How to actually ruin a knife:
Over heating: if the blade is heated to above 400°F then the temper will be ruined and it will not hold an edge. If a blade is overheated, it will show a purple or blue oxidation on the surface. This could happen by leaving it too near a grill, burner or stove eye.
Dishwasher: Anything a but a plastic handle will eventually be destroyed in the dishwasher. They often use steam to clean dishes which is above 212°F. This is always destructive to wood handles or really any finely made knives. It’s just stupid to put any sharp knives into the dishwasher because they clang around in there against other steel silverware and dishes, dulling the edge. Just wipe and put away your knives when you finish using them - one less thing to do later. It actually takes more time to load and unload them than it does to wipe and store knives immediately.
Leaving knives in the sink: Soaking knives in the sink is almost as bad as the dishwasher with the added spice of danger when you have to reach your fingers down below the bubbles to feel around for that freshly sharpened blade. Leaving them dry in the sink will lead to rust more quickly as the air/water interaction is increased since the knife is not submerged. Let’s face it, in the kitchen knives belong either in their storage, in your hand or on the cutting board.
Over grinding: In unskilled hands, taking a knife edge to a powered grinder is the worst thing that can be done. First there is the risk of overheating as the friction heat increases while grinding. Then the main issue is just removing so much more metal than necessary. I have seen knives that could have lasted decades used up in months by over grinding. Frequent touch up and edge maintenance avoids the need to rebevel a knife. Long live the bur!
That is: Strop, or Die.