5 Ways to Fix a Rusty Knife

Owning a knife can be really helpful, especially if you go camping or engage in any other outdoor activities that may require you to use a knife. Still, a knife comes with many benefits regardless of use – and this is why you have to protect it properly or know what to do when such a tool has been rendered useless.

Naturally, we refer to rust – Iron (III) Oxide which is formed when the Iron of the knife’s blade combines with the Oxygen present in the atmosphere. While some of you may prefer using a survival knife, given that these don’t rust easily, most of the knives we own will most likely be affected by rust – depending on the environment we keep them in.

Therefore, in today’s article, we’ll be taking a closer look at rust, rusty knives, and we’ll give you 5 tips to help you fix a rusty blade and make your knife look brand new!

The Cause of Rust

Before talking about how to fix it, it’s important to know what exactly causes rust so that you know how to prevent it from happening.

There are three main ingredients that cause your knife to rust, namely water, oxygen, and iron. Obviously, all of them are required to come in contact. Iron is found in the knife’s blade, oxygen is everywhere around the knife itself, and water – mostly in the form of moisture – will favor the formation of rust.

Naturally, you have no influence over the first two ingredients. You can’t keep the oxygen away from a knife and you certainly can’t use it if it has no blade. What you can keep away from the knife is moisture.

However, keep in mind that moisture does not have to be liquid, so to speak. For example, humid air is enough to cause rust. 

Basically, you have to keep these three ingredients away from each other if you don’t want your knife to rust – shortly put, keep your blade away from moisture.

Types of Steel

The material from which the blade of a knife is made can influence the time when rust forms. The blade can be made of either Stainless steel or Carbon steel. Carbon steel comes with additional carbon in its composition (around 0.5% to 1.5% carbon), while Stainless steel comes with Chromium (12.5% to 13.5%).

Carbon steel knives, while durable and very strong, are also prone to corrosion if they are not being taken care of. Such knives will easily rust in acidic or humid environments.

On the other hand, the Chromium inside a Stainless-steel blade creates an oxide layer on its surface, preventing the steel from further oxidation. Therefore, the corrosion is slowed down – hence the name Stainless.

Ways to Fix a Rusty Knife

Given that a high-quality knife is a valuable – and sometimes pricey – tool, you must know how to fix a rusty one. However, if you don’t, then you’ve come to the right place.

In the following lines, we’ll show you five of the best ways to deal with a rusty knife and make it as sharp and shiny as it was when you first bought it.

• Baking Soda

The use of baking soda is one of the easiest ways through which you can fix a rusty knife. First, you have to apply water to the rusted area and then sprinkle some baking soda on it. 

The baking soda that comes in contact with the wet area should stick to it. You should also remove any excess baking soda by gently tapping the knife.

After a couple of minutes, scrub the area covered by baking soda with a wet scrubbing pad. Remember that the scrubbing pad must be wet at all times while doing this so that the blade doesn’t get damaged.

With a few minutes of scrubbing, the rust should come off. If required, you can repeat the process. After the rust is gone, rinse the knife with water and then wipe it dry.

• Vinegar

Just like baking soda, this is yet another item that you can find in your kitchen – no need for you to go shopping.

Start off by pouring white vinegar into a pan or a wide container. Then, take your knife and soak it in the vinegar – you can choose whether to soak the entire knife or just the blade. Keep it there for about 5 minutes. 

After that, wipe the blade with a cloth, rinse it with water, and then dry the knife.

Do not leave the blade in vinegar for too long, as the latter can damage or stain it.

• Chemical Solvents

Naturally, you can find numerous chemical solvents that can be used to remove rust from the blade of a knife. However, you have to make sure that they are not toxic, especially if you plan on preparing food with that knife.

Before spraying the knife with any solvent, make sure to clean it with oil in order to remove impurities or stains. After spraying it, use thin sandpaper to remove the rust stains. 

Repeat this process until the rust is gone, then wipe, rinse with water, and dry the knife.

• Sandpaper

Keep in mind that sandpaper is usually used for small rust stains. The rust stain has to be rubbed gently with a piece of fine sandpaper. Thicker sandpaper can damage your blade and larger rust stains can take quite some time to remove.

We recommend you use a 3000-grit product when scrubbing off the rust – any bigger value could remove the finish of the blade, scratch it, dull it, and damage it.

• Natural Products

Some methods don’t require any special products or equipment. For example, you can simply stick your knife in a potato and leave it there for a few hours. Potatoes contain oxalic acid, which is known to dissolve rust.

You could also stick the blade in rich soil – actually, plunge it in dirt – and then wipe and rinse it. However, make sure that the soil isn’t too rough, or you’ll damage the blade.

If you have a lemon available, cut it in half and rub it across the part of the blade that has rust on it. If you have to deal with a larger rust stain, you can let the lemon sit on the stain for an hour or so. Remember to scrub after you’re done!

Finally, if you don’t mind some tears, then you can stab an onion with your rusty knife, saw back and forth into it, and then scrub off the rust. The sulfenic acids within the onion will help dissolve iron oxide – the main compound of rust.

The Bottom Line

As you can see, you don’t need any special products to fix a rusty knife. In an emergency, you can just plunge it into the closest patch of rich soil and see the results for yourself.

Still, even if fixing a rusty knife seems quite easy to do, it is important that you know how to prevent rust from forming on the blade. In short, keep moisture away from it – avoid storing the knife in humid environments and, obviously, don’t leave it outside during the rainy season.