Similar to other carbon steel products, carbon steel knives are prone to rust. And even if your knife is made of stainless steel, rust can still form if you don’t take proper care of it.

Luckily, rust on your carbon steel knives isn’t necessarily a death sentence; you can still remove rust off the blades using multiple DIY techniques. 

Based on my expertise as a knife enthusiast, and since I’m an expert when it comes to knife maintenance, I’ve crafted this guide to walk you through everything you need to know about cleaning carbon steel knives.

Why Does Carbon Steel Rust Easily?

Steel is made up of iron, carbon, and a few other elements. And since iron, in particular, is highly prone to oxidizing, it forms a layer of rust when exposed to air.

A form of carbon steel, called stainless steel, has high chromium content, which protects it from rust by forming a chromium oxide layer that prevents oxygen from reacting with iron and forming iron oxide (rust).

The chromium oxide layer often gives stainless steel a greyish/dark-green hue. So, if you see something like that on your knife, don’t panic; it’s not rust!

At What Rate Does Carbon Steel Rust?

According to a paper published by IOP Science, the rate at which carbon steel rusts is between 6.64 and 7.01 mpy. But that study was carried out on a test piece of carbon steel soaked in a river, not a knife blade within your household, so don’t expect your knife to rust at the same rate.

Setting aside the technical stuff, the actual rust rate of your carbon steel knife varies according to a wide range of factors such as the weather and humidity of your location, the kitchen’s temperature, and so on. 

But as a general rule of thumb, carbon steel is most exposed to rust when the humidity is somewhere between 70 to 80%, and the temperature is above 30° Fahrenheit. And, of course, the more impurities in the surrounding environment, the faster rust will form.

Also, some elements, such as table salt, can act as a catalyst for the rusting process.

How to Clean Carbon Steel Knives?

There are multiple ways to clean carbon steel knives, and thankfully, none of them require any special ingredients or tools that aren’t already available in your kitchen. So, here are the four best methods to clean your carbon steel knives:

Method 1: The Vinegar Method

The easiest and most available way to clean carbon steel knives is to use white vinegar. White vinegar contains acetic acid, which has the ability to eliminate rust off the steel. 

Here’s how to clean your carbon steel knives with white vinegar:

• Pour some white vinegar into a glass container and dip the knives in it
• Leave the knives in white vinegar overnight
• Use a wire brush to scrub the blades until you can’t see any rust residue
• If you think that the knives aren’t clean enough yet, soak them in a new vinegar solution for another night
• Once your blades are rust free, clean them with dishwashing soap and water and dry them immediately

On a side note, make sure that you only use white vinegar, not any other type, to prevent any discoloration.

Method 2: The Baking Soda Method

This one is a bit tricky since you might damage your knife, but it’s quite effective and guaranteed to remove even the most stubborn layers of rust.

Here’s how to do it:

• Use a non-abrasive cleaning solution and a lint-free cloth to clean your knife’s blade
• If you use water, make sure that the knife is fully dry before proceeding to prevent rust from building up even more
• Mix baking soda with water to make a paste
• Apply the paste to each side of the blade, one at a time
• Wait for 10-15 minutes and use a ball of steel wool to scrub the side with the paste on it
• Repeat the paste process for the other side 
• Reapply the paste if needed
• Once all the rust has been removed, use a dry cloth to wipe the knife thoroughly
• This step is optional, but if you add some mineral oil to the knife’s blade after you’re done, you’ll be adding a protection layer to the steel, thus preventing future rust

It’s also recommended that you resharpen the blade after you’re done because abrasive materials like baking soda can dull out the knife’s blade; any hard stone will get the job done, and you can always opt for a ceramic sharpener as well. 

Of course, if the knife is precious for you and you want to keep it scratch-free, you might want to use a wine cork or balled-up aluminum foil instead of steel wool. 

These materials are less abrasive, so the risk of scratching the knife or dulling the blade decreases dramatically. However, keep in mind that these alternatives may take a while longer than steel wool.

Method 3: The Lemon and Salt Method

Another easy way to clean your carbon steel knives is to use lemon and salt. These two ingredients are capable of removing rust from your carbon steel knives. 

Since lemon is acidic, it works just as effectively as the acetic acid found in white vinegar. In addition, salt acts as a sharp ingredient that complements the acidic effect of lemon, allowing you to get rid of any traces of rust on your blades.

Now, let’s walk you through the steps needed to clean your knives with lemon and salt:

• Start by applying some salt to your knife 
• Pour lemon juice on the required areas
• Wait for two or three hours and use a wire brush or the lemon rind to scrub off the rust layers
• Wash the knife and dry it immediately

Method 4: The Bar Keepers Friend

The Bar Keepers Friend is a cleanser that does a great job of removing rust layers from knives. It’s available at most retail stores, and you can even grab one online. 

However, it’d be best if you keep this technique as your last resort because, in most cases, you don’t really need to purchase a specialized cleaner to scrub some rust off your blades. 

I understand that some rust layers can be pretty stubborn, though, which is why I’ve added this method right here for you. 

The good thing about this technique is that you don’t need to use any abrasive materials, ensuring that the blade’s integrity isn’t affected.

To clean your knife with the Bar Keepers Friend, do the following:

• Put some Bar Keepers Friend on your knife’s blade, particularly on the rusty areas
• Rub the blade with a wet sponge and leave it for 5-10 minutes
• Wash off any product left on the blade and use a dry cloth to dry the blade
• Make sure that the blade is 100% moisture-free to prevent another layer of rust from forming

Final Words

Alright, so that was a quick overview of the best ways to clean your carbon steel knives and restore their shininess! And I believe you’ll be satisfied with the results whether you use white vinegar, salt and lemon, baking soda, or the Bar Keepers Friend.

Also, remember that the golden rule when it comes to maintaining your knives, whether they’re kitchen or Swiss army knives, is to properly clean them after each use and dry them immediately afterward since water can accelerate the development of rust layers.

It’d also be a good idea to keep your knives away from humid environments since rust almost always forms when the humidity exceeds a particular threshold.