Do you remember being told as a kid that stepping on a rusty nail could give you tetanus? Believe it or not, that old piece of knowledge is actually a half-truth and ignores a number of important facts about the disease. Sure, you can get tetanus from that old, rusty nail — or from anything else that makes a break in the skin. It’s not the rust itself that causes the illness, but the specific bacteria present in the environment. In fact, unless you inhale rust day after day after day or have a rare condition such as hemochromatosis, rust poses you no health risk. Who would have thought it? The same, though, can’t be said for your knives. For them, rust blunts their sharpness, destroys their structural integrity, and (perhaps most importantly!) simply makes them look ugly.
Why Does Rust Happen in the First Place?
Rust is a kind of corrosion, and it occurs when a specific chemical process takes place. When moisture comes in contact with metal (steel and its many variants, in our case since we’re talking about knives), it causes the iron, steel, or some similar ferrous material to lose electrons to the oxygen in the water molecules. The result is a chemical reaction that forms iron oxide, the flaky, orangey stuff that we dub rust.
The primary concerns that most people will have regarding rusty knives are two-fold: aesthetic and functional. If you have guests over and they see you preparing a meal with a dappled knife, don’t be surprised if they find their food less than perfectly appetizing. And should you put a blade through its places in an outdoor context without properly cleaning and storing it, oxidation might eat it away until cutting becomes a struggle or it chips and breaks. Given their various moving parts and tight manufacturing tolerances, OTFs don’t tolerate rust well. A little corrosion, some swelling, and suddenly your favorite knife just won’t open.
Fortunately, finding a few spots of rust doesn’t spell doom. Following are some tried-and-true methods for cleaning rust from knives.
One of the most common — and the easiest! — ways to remove rust from a knife is with vinegar. First things first, though: Before you attempt any of the methods in this article, make sure to clean off your knife. Dirt, grime, and (in particularly bad cases) excess oxidation can prevent you from fully getting the rust off of your blade.
Applying white vinegar to a rusty piece of metal combats oxidation on two fronts. The first is chemically through acetic acid, which white vinegar contains and is one of the substances known to dissolve rust. While white vinegar isn’t the only kind of vinegar that contains this acid, it is the one that won’t discolor, stain, or damage your knife so long as it’s only applied for a few minutes. Acetic acid isn’t the only option for dealing with rust and we’ll examine another in a following section, but it is one of the easiest to work with. Strong acids such as hydrochloric acid, phosphoric acid, sulfuric acid, and the like will completely remove or transform rust. However, they pose a significant risk to people. Since it’s a weak acid, acetic
acid doesn’t, and submerging a blade in white vinegar for a few minutes should partially dissolve the rust.
The second front on which white vinegar works is less technical. Apply some elbow grease after treatment, which should cause any remaining rust to flake off. In what will become a theme for many rust-removal solutions, don’t scrub too hard or you could end up damaging the metal itself or the knife’s finish.
Lemons put the power of citric acid to work, which is somewhat similar to acetic acid and similarly effective. You can apply it the same way by either juicing lemons or rubbing them on the affected metal. You can also purchase and apply powdered citric acid. No matter which path you choose, you will need a lot of scrubbing and multiple applications to get rid of all the rust.
Potatoes or Onions
This pair of produce products provides yet more acidic options. Onions contain sulfenic acid, while potatoes possess oxalic acid. (You may recall that we used oxalic acid as an example of a strong acid, one that posed a risk to humans. The naturally occurring levels of oxalic acid present in potatoes, though, are safe. Just don’t eat a bushel in a single sitting.) The gist of using of using these vegetables as rust removers should be familiar by now. You can stick the knife in either and leave it there for a while or rub a freshly cut slice against the metal. Throw in some burnishing afterward to eliminate the oxidation.
Baking Soda or Salt — or Dirt
The techniques listed in this subsection don’t rely on chemistry at all. Indeed, the chemical compositions of these substances run counter to the ‘”acid eliminates rust” axiom on which we’ve thus far relied. Baking soda is a base, and salt is a crystalline mineral. They don’t actually react with oxidation, although one can combine them with the previously mentioned approaches to increase their effectiveness. Instead, these materials rely on their abrasiveness to do their work.
To start, either apply baking soda or salt along with a very small amount of water. Excess liquid or moisture will rob both of their polishing power, particularly salt, which will simply dissolve. For baking soda, you can leave the paste applied for up to an hour, and that may help it better bind to the rust. Then take a slightly rough cleaning pad of some kind or a toothbrush to the metal and start scouring. Note that this approach will only eliminate small surface blemishes. If you’re trying to get rid of deeper pockets, you will need to add some sandpaper or steel wool. Understand that doing so runs the risk of permanently damaging your knife if you aren’t careful.
Speaking of risk, we should address the elephant in this subsection’s title. You can, indeed, use dirt to get rust off of a blade. In fact, it works just like baking soda or salt. When you stick a knife into the earth and remove it, rough particles of soil polish away oxidation — albeit with far more significant downsides. An accidental encounter with a stone could lead to chips. Dirt will inevitably dull an edge. And since soil is usually somewhat damp, you could end up making the rust issue worse. Save the dirt method for dire situations only.
For those who don’t mind using a commercial product, WD-40 comes in multiple formulations that can remove and deter rust (e.g., regular WD-40, WD-40 specialist rust remover soak, WD-40 specialist corrosion inhibitor). It works much like the other chemical options. Apply WD-40 directly or submerge the affected metal in the liquid. After 15 minutes, scrub the rusty area with your implement of choice. Make sure not to use WD-40 on any knives designed for food preparation or consumption since it can expose people to potentially dangerous compounds.
Our final suggestion is one of the most effective ways of eliminating rust, but also one of the most challenging to set up. Broadly speaking, the term electrolysis refers to a method of using direct electric current to start some kind of chemical reaction, the exact nature of which depends on the end goal. Electrolysis is used in the commercial production of hydrogen, chlorine, sodium chlorate, sodium hydroxide, and potassium chlorate. Some industries employ it metallurgically with lithium, aluminum, copper, calcium, potassium, and sodium. You may even have seen advertisements for permanent hair removal that mention electrolysis. In cosmetic contexts, it eliminates follicles by creating sodium hydroxide. Fortunately, rust-removing electrolysis requires little in the way of equipment compared to these industrial uses and can be performed by just about anyone with a well-ventilated area.
The kind of electrolysis involves submerging a tool in a container filled with an electrolyte solution (easily created by dissolving washing soda in water) and running a low-voltage current through the liquid by means of an iron electrode or a scrap piece of steel connected to a battery charger. Learn more about creating your own electrolysis device here. When the current encounters rusty metal in the electrolyte solution, it converts some of the rust to iron, allowing the more severely affected areas to shed their remaining oxidation. Note that electrolysis can produce unsafe fumes, so don’t attempt it in an enclosed space.
How To Prevent Rust from Forming on Your Knives
No matter how well a particular rust-removal method works, it will still require significant time and effort. Sometimes, you may find that your knife just isn’t the same even after getting rid of oxidation. Perhaps it got significantly dulled or the finish became scuffed or an abrasive scored a deep scratch down the blade’s flat. No matter one’s rationale, it’s easier to avoid rust in the first place rather than to try and fix it.
In this section, we’ll talk about the ways in which you can keep your knives from getting rusty when used or stored
Clean and Dry Your Knife Immediately After Use
This one is something of a no-brainer, but it can be harder to implement than you might think. Life is busy, and when you’re trying to set up camp in the wilderness, quickly slicing an apple while on break, or get caught in a thundershower while whittling, it just might slip your find. Here’s one tip you shouldn’t forget, though: Make sure your knife doesn’t come into contact with salt water, and if it does, make thorough cleaning and storage a top priority.
Sheathe or Store Your Knife When Not in Use
Speaking of storage, sheathing your knife is an excellent way to protect it from moisture. However, simply buying and using a sheath isn’t enough. You should care for it much the same as you care for your knife. Ensure that it’s clean and dry every time you put your knife away, and prioritize selecting one that won’t discolor or fall to pieces when washed with soap and water.
Use Soft Implements When Cleaning a Knife
The same scouring pads and wire brushes that work so well to remove rust from a blade can also damage its finish and scratch its metal. Sometimes you’ll have to resort to force in order to preserve a knife from oxidation. But only use soft cloths and similar implements when performing everyday cleaning tasks.
Regularly Sharpen Your Knife
An ancient proverb states, “If the iron is blunt, and one does not sharpen the edge, he must use more strength, but wisdom helps one to succeed.” Wisdom would doubtlessly say, “Sharpen your knife!” Not only does it make any cutting tasks easier, it also protects it from damage. Working with dull blades requires excessive force, and using such force may lead to chips, cracks, or the blade straight up snapping.
Treat the Blade with Oil or Wax
Since water is such an essential part of the oxidation process, regularly applying a hydrophobic substance such as mineral oil or a wax specially formulated for knives will go a long way toward protecting a knife. Options abound, but if you plan to use your knife to prepare or consume food, pick a non-toxic material.
Force a Patina on Carbon Steel
Though carbon steel is an excellent material, it’s prone to rusting. One of the ways to protect it involves forcing a sacrificial patina on its exterior. Methods vary. Some swear by boiling vinegar and immersing the blade in it for roughly 20 minutes. Others prefer brewing the strongest, nastiest pitcher of coffee you could imagine and leaving the blade in it overnight. Either method will leave a patina on the knife that will safeguard it against rust. Note, though, that it will eventually rub off and require another application.
No matter your preferred style of knife, you’ll need to take steps to protect it from and eliminate any rust. Browse our selection of knives here.