How To Remove Rust From Metal Knives | Knife Depot

Whether you’ve found a knife in one of your old toolboxes or accidentally left your favorite knife outside in the rain, chances are you have encountered a nasty case of rust.

While some old-school knife users believed a little rust was the mark of good, high-carbon steel, the truth is that rust weakens the blade, ruins its looks, and can even make it unsafe to use.

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We originally wrote this post way back in December 2011, but we thought it’d be a good idea to do update it with some better information, videos, and recommendations.

What is Rust?

If you’re just here for rust removal tips, feel free to skip ahead — but understanding why your blade rusts can help you prevent it in the future.

Let’s start with the basics: rust is actually iron oxide, the reddish-orange flaky substance that forms when iron reacts with oxygen and moisture. And it doesn’t take direct water contact — even humidity in the air can be enough.

Here’s a more scientific explanation from How Stuff Works:

Iron (or steel) rusting is an example of corrosion — an electrochemical process involving an anode (a piece of metal that readily gives up electrons), an electrolyte (a liquid that helps electrons move) and a cathode (a piece of metal that readily accepts electrons). When a piece of metal corrodes, the electrolyte helps provide oxygen to the anode. As oxygen combines with the metal, electrons are liberated. When they flow through the electrolyte to the cathode, the metal of the anode disappears, swept away by the electrical flow or converted into metal cations in a form such as rust.

Why Do Knives Rust?

Here are the ingredients for rust: iron, water, and air.

For those who don’t know, iron is the secret ingredient of the steel found in your knife blades. So when you mix your knife with air and moisture, you eventually get rust.

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“But, wait, my blade is stainless steel,” you might be thinking. Sadly, stainless steel is only stain-resistant, not stain-proof. (As the saying goes, “stainless, not stainfree.”) I’ve explored the myth of stainless steel before, but here’s the quick version: stainless steel must contain at least 10.5% chromium, which helps form a protective layer against corrosion.

Still, that doesn’t make it invincible. As long as it’s steel, it can rust under the right conditions — unless it’s something like ceramic.

There is one possible exception: H1 steel, often used in Spyderco’s Salt Series. H1 has very little carbon and tons of chromium, making it nearly impervious to rust. A few unverified reports have claimed H1 rusted after years at sea, but those cases remain rare and unconfirmed.

How to Remove Rust from Your Knife

You can use these methods individually, together, or repeat them for especially stubborn rust. Once you’ve finished removing the rust, I highly recommend sharpening your blade to restore its edge and ensure it’s safe and ready for use.

Method #1 – Baking Soda to Remove the Rust

“Close-up Of Baking Soda On Spoon” by Aqua Mechanical is licensed under CC BY 2.0

Materials: Baking soda, water, toothbrush, steel wool (or sponge), cloth

1) Clean Your Knife

Start by thoroughly cleaning the blade to remove any dirt or debris, which can get in the way of rust removal. Avoid using water since moisture likely caused the rust in the first place.

Instead, use a cleaning solution and wipe the blade down with a cloth.

2) Create Baking Soda Paste

Mix a generous amount of baking soda with a bit of water (or lemon juice) in a bowl. Stir until it forms a thick paste.

3) Scrub with toothbrush

Apply the baking soda paste to a toothbrush and liberally spread it over the rusted areas. If the rust isn’t too deep, scrubbing with the toothbrush alone may be enough.

4) Use steel wool or an abrasive sponge

For tougher rust, you’ll need a more abrasive tool. Lightly scrub the blade with steel wool or a mildly abrasive sponge. Be careful not to press too hard to avoid scratching the blade or damaging the finish.

5) Wipe the blade clean

After removing the rust, wipe the blade down with a clean cloth to get rid of any leftover baking soda. For extra protection, apply a light coating of mineral oil to help prevent future rust.

Our old friends at Taylor Brands (we miss you) made a video demonstrating this method if you’re more of a visual learner.

Method #2 – Vinegar Bath for Removing Rust

“Vinegar” by Chris Martin is licensed under CC BY 2.0

Materials: Pan or cup, white vinegar, sponge, cloth

1) Pour vinegar into a cup or pan

Use white vinegar, which contains acetic acid that helps break down rust. Avoid other types of vinegar, as they may leave stains on the blade.

2) Soak the rusty knife

Submerge the rusty parts of the knife in the vinegar. If you prefer not to soak the entire blade, soak a paper towel in vinegar and wrap it around the affected area. Let it sit for about five minutes — any longer, and you risk damaging the blade.

3) Wipe down the blade

After soaking, wipe the blade clean with a cloth. If any rust remains, you can follow up with the baking soda method or a rust remover like WD-40. Finish by applying a light coat of mineral oil to protect and condition the blade.

Here’s a cool video showing the power of vinegar on a dive knife

Method #3 – WD-40 As Rust Remover (Best for Larger, Non-Food Prep Knives)

“WD-40” by FHKE is licensed under CC BY 2.0

Materials: WD-40, fine sandpaper, cloth

I recommend this method for larger knives like machetes or blades not used for food preparation, as WD-40 can be harmful if ingested. It’s a fast and effective way to remove rust, but do not use WD-40 as a lubricant afterward.

1) Spray WD-40 on the blade

Spray a light coat of WD-40 directly onto the rusty areas of the blade.

2) Gently sand the blade

Using very fine sandpaper (around 400 grit), carefully sand away the rust. Avoid sanding the edge itself, as it can damage the sharpness.

3) Wipe it down

Once the rust is removed, wipe the blade clean with a cloth. For heavier rust, you might want to repeat the process or try one of the previous methods. Again, avoid this method if you intend to use the knife for food preparation.

Natural Knife Rust Removal Methods

When you don’t have the materials around the house to get rust off your knife, there are a few natural methods you can use.

Potato Method

Certain foods can surprisingly help remove rust, and one of the best is the humble potato. Thanks to its natural oxalic acid, a potato can work wonders on a rusty blade.

Simply stick your knife into a potato for a few hours. After removing it, wipe the blade clean and apply a light coat of oil. The rust should come off easily, leaving your blade looking much better.

Onion to Remove Rust from a Knife

Onions are another natural way to tackle rust. Simply saw the blade back and forth through an onion, and you’ll start to see the rust lift off on its own. The secret lies in the sulphenic acids released by the onion, which help break down the rust and clean the blade naturally.

Dirt Method

Another natural method people often recommend is using soil. Simply plunge your rust-covered knife into rich, moist soil about two dozen times. Afterward, wipe the blade clean. The slight abrasiveness and natural moisture in the soil can help lift away surface rust.

Everyone has their own method, so let us know in the comments what you do.

Grab a New Knife!

If your knife is beyond the amount of work you’re willing to put into it, it’s OK to move on.

We have thousands of knives in stock that you’re welcome to look at. Shop our catalog and buy knives online today.