Rust on Knives: What Causes It and How to Avoid It

Author: Joost Nusselder, author of The Essential Japanese meal planner cookbook Updated November 3, 2022

Have you ever picked up a knife and it was all rusty? It’s a pretty gross sight, but it happens to the best of us.

Rust is a natural process that occurs when iron comes into contact with oxygen and moisture. It’s a slow process that happens over time, but there are ways to prevent it. 

In this article, I’ll explain why knives rust, and I’ll share some tips on how to prevent it from happening.

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Understanding Rust on Knives

Rust is a term commonly used to describe the oxidation of iron and steel. Technically, rust is hydrated iron oxide, a compound formed when iron reacts with water and oxygen in the presence of carbon dioxide. Rust is inevitable with exposure to oxygen and moisture, and the intensity and speed of rust growth depend on the quality of the steel and the environment it’s exposed to.

Why are knives prone to rust?

Knives, especially those containing high amounts of carbon, are highly prone to rust. Carbon steel knives are hardy and fairly resistant to bending, but they can easily lose their sharp edge and rust when exposed to moisture. Stainless steel knives, on the other hand, usually contain highly resistant alloys like chrome and nickel, but they are more prone to bend and lose their sharpness instead of rusting.

What Causes Rust?

Rust is a natural process that occurs when iron or steel is exposed to oxygen and moisture. When a knife blade is exposed to the atmosphere, the oxygen in the air reacts with the iron in the blade to form iron oxide, also known as rust. This process is sped up in the presence of salt or other impurities, making knives used in humid or salty conditions more susceptible to rust formation.

Carbon Steel Knives are More Prone to Rust

Carbon steel blades contain a higher amount of carbon, which makes them highly prone to rust. Manufacturers often prefer to use materials containing chromium, a strong alloy that has higher resistance to rust formation. Stainless steel, for example, is comparatively inert and entirely impervious to rust.

Proper Storage Can Help Prevent Rust

To prevent rust formation, it is recommended to properly store knives away from humid or salty conditions. Cutco, a favorite brand among chefs, recommends storing knives in a dry environment and wiping them down after use to remove any excess moisture.

Ways to Remove Rust from Knives

If rust does begin to form on a knife blade, there are different tried and true methods to remove it. One method is to create a paste using baking soda and water, and then spread it thickly over the rusted area. Let it sit for a few minutes before scrubbing it off with a dish brush. Another method is to soak the knife in a mixture of white vinegar and water overnight, then wash it with soap and water. For minor rust spots, soaking the knife in a glass of cola for a few minutes can also help remove the rust. However, if the rust is too extensive or has damaged the blade, it may be best to seek professional help or replace the knife altogether.

Rust not only looks ugly on a knife, but it can also be dangerous if excessive rust is allowed to grow. By understanding the main factors that favor rust formation and taking proper precautions, knives can be safely used and stored to prevent rust from forming.

Understanding Pit Corrosion in Knives

Pit corrosion is a type of localized corrosion that affects metals, including those used in knives and cutlery. It is a natural reaction that occurs when metals are exposed to a salty or acidic environment, and it can happen to any type of steel, although some are more susceptible than others.

How Does Pit Corrosion Happen?

Pit corrosion happens when the metal’s oxide layer is damaged, allowing the metal to come into contact with the environment. This exposure causes the metal to oxidize, which forms a thin layer of rust that closes off the pit and protects the metal from further exposure. Normally, this process happens slowly and is not a problem, but if the environment is moist or there is a drop in pH, there is a chance that pit corrosion can form.

How Can You Prevent Pit Corrosion?

Preventing pit corrosion is easy if you follow a few simple steps:

• Clean your knives immediately after use and dry them thoroughly.
• Avoid leaving knives in a wet sink or work surface.
• Sharpen your knives regularly to prevent damage to the cutting edge.
• Avoid using chrome or water to clean your knives, as this can increase humidity and damage the metal.
• If you have a wooden handle, make sure it is precisely transitioned to the steel to avoid any spots where rust can be generated. If rust spots are already present, they can be removed with a soft cloth and a bit of abrasive.
• Store your knives in a dry environment to prevent exposure to moisture.

Remember, prevention is key when it comes to pit corrosion. By taking care of your knives and keeping them dry, you can avoid this type of damage and keep your knives in top condition for years to come.

Factors that Affect Rust Formation on Knives

It is a common misconception that Japanese knives are more prone to rusting compared to other types of knives. However, the truth is that any knife can rust if not properly taken care of. Factors such as the material of the blade, exposure to moisture, and prolonged use can all contribute to the formation of rust.

Tips for Preventing Rust Formation on Knives

To prevent rust formation on your knives, pay attention to the following tips:

• Clean your knives immediately after use and dry them thoroughly.

• Avoid using rough scourers or abrasive detergents that can scratch the surface of the blade and expose the underlying material.

• Store your knives in a dry and well-ventilated area.

• Use a mineral oil or a protective coating to protect the blade from moisture.

• If you own a Japanese knife, pay attention to the manufacturer’s recommendations for cleaning and sharpening.

• Consider investing in knives made of materials such as titanium, pure molybdenum, or other alloys that are less prone to rusting.

In conclusion, while some types of knives may be more prone to rusting than others, proper care and maintenance can help prevent rust formation and prolong the life of your valuable kitchen appliance and cookware.

Why Japanese Knives Rust: Understanding the Factors

Japanese knives are known for their unique characteristics, such as their sharpness and durability. However, they are also prone to rusting, which can affect their performance and lifespan. The main reasons why Japanese knives rust include:

• Exposure to air: When the blade of a Japanese knife is exposed to air, it can form an oxide layer that causes rust to form.

• Carbon steel material: Many Japanese knives are made from carbon steel, which produces a sharp edge but is also prone to rusting.

• Contact with moisture: When a Japanese knife comes into contact with water or moisture, it can hasten the formation of rust.

• Soaking or leaving wet: Leaving a Japanese knife soaking in water or leaving it wet for an extended period can also contribute to rust formation.

Factors That Affect the Rusting of Japanese Knives

Several factors can affect the rusting of Japanese knives, including:

• Type of material: Japanese knives made from hagane, which contains carbon, are more prone to rusting than those made from stainless steel.

• Exposure to oxygen: When a Japanese knife is exposed to oxygen, it can cause rust to form.

• Contact with acidic or salty substances: Japanese knives that come into contact with acidic or salty substances, such as citrus fruits or salt, are more likely to rust.

• Cleaning and maintenance: Proper cleaning and maintenance can delay the onset of rusting and prolong the lifespan of a Japanese knife.

How to Prevent Rusting in Japanese Knives

To prevent rusting in Japanese knives, it is essential to take proper care of them. Here are some tips:

• Wash and dry the knife after each use: This will help to remove any moisture and prevent rust formation.

• Store the knife in a dry place: Avoid storing the knife in a damp or humid environment.

• Use a ceramic or wooden cutting board: Avoid using metal or glass cutting boards, which can damage the blade and hasten rust formation.

• Avoid soaking the knife: Do not leave the knife soaking in water or leave it wet for an extended period.

• Clean the knife properly: Use a mild detergent and warm water to clean the knife, and dry it thoroughly afterward.

In conclusion, Japanese knives are highly prized for their unique characteristics, but they are also prone to rusting. Understanding the factors that contribute to rust formation and taking proper care of the knife can help to delay the onset of rusting and prolong its lifespan.

Rust on Carbon Steel Knives

When it comes to choosing a knife, the type of steel used in the blade is critical. Carbon steel is a popular choice for knives due to its ability to retain a sharp edge and its durability. However, it is also prone to rusting, especially when exposed to moisture and oxygen. Here are some finer points to know about carbon steel:

• Carbon steel is a type of steel that contains carbon as the primary alloying element.
• It tends to be softer than stainless steel, which makes it easier to sharpen but also more prone to corrosion.
• Carbon steel tends to form rust spots quickly when exposed to moisture and oxygen.
• However, it also tends to hold its edge for longer periods of time, making it a popular choice for chefs and home cooks who require precision when dicing and slicing.

Why Does Rust Occur on Carbon Steel Knives?

Rust on carbon steel knives occurs when the presence of moisture and oxygen speeds up the oxidation process. When a knife is wet and allowed to stay that way for an extended period of time, the oxidation process is sped up, resulting in rusty spots on the blade. Despite being harder than stainless steel, carbon steel is also easier to corrode due to its softer nature.

An Anecdote on Rusty Knives

If you’ve ever wondered why a knife feels different after being used to cut something like meat, the actual object or substance being cut can offer minimal protection against rust. I once noticed blood dripping from a freshly sliced piece of meat and stared in horror as I realized my old carbon steel knife had sliced through several layers of fabric in the process. The key elements to keep in mind when choosing a knife are the type of steel used and the level of care required to maintain it. Carbon steel knives are incredibly durable and can retain a finely honed edge for a long time, making them a popular choice for home cooks and expert chefs alike. However, they require frequent maintenance and effort to prevent rust from forming.

Why Knives Rust in the Dishwasher

When it comes to washing knives, the dishwasher seems like the ultimate solution. It’s quick, easy, and requires minimal effort. However, it’s not always the safest option for your knives. Here’s why:

• Knives are made of different metals, and some are more susceptible to rust than others.
• When knives come into contact with salty or acidic food, it can speed up the corrosion process.
• The dishwasher environment is a perfect place for rust to form, with an abundance of water and oxygen present.
• When knives are washed in the dishwasher, they are often sitting in a crumbing and persistent environment until the dishwasher is emptied.
• The quick wash cycle is unlikely to remove all the food particles, which can result in rust.

How to Minimize the Chance of Rust

If you’re looking to keep your knives in top condition, it’s best to avoid the dishwasher altogether. Here are some tips to help you keep your knives rust-free:

• Hand wash your knives with warm water and soap, then dry them immediately.
• Wrap your knives in a vacuum-sealed bag to prevent exposure to oxygen.
• Store your knives in a dry environment, away from other metal items that can cause scratches.
• Regularly oil your knives to prevent rust from forming.

Using Rusty Knives: Is it Safe or Not?

Rust on knives can be disappointing and ugly to look at, but it’s not just a cosmetic issue. When a knife is exposed to air and moisture, a chemical reaction occurs that creates a compound called iron oxide, or rust. This substance grows on the blade and reacts with any salty or acidic foods it comes into contact with, potentially compromising the safety of your food.

Can You Continue Using Rusty Knives?

The short answer is no. Rusty knives are not safe to use, as they can expose the underlying metal and create nicks and rough spots that can harbor bacteria. Additionally, the luster of the blade can be damaged by rubbing or scourers, making it more prone to rusting in the future.

How to Get Rid of Rust on Knives

If your precious Japanese carbon steel knife appears to have rust spots, don’t panic. There are multiple solutions available to help you restore it to its original state. Depending on the extent of the damage, you may need to introduce chemicals or cleaners to fully rid the blade of rust. Some suitable options include citric acid, baking soda, or even a potato.

How to Protect Your Knives from Rust

To protect your knives from rust, it’s important to pay attention to the materials they contain and how you handle them. Here are some tips to help you keep your knives in top condition:

• Choose knives made from alloys that are less prone to rusting, such as those containing chromium or molybdenum.
• Avoid exposing your knives to moisture or salt for extended periods of time.
• Dry your knives off immediately after use to prevent rust from forming.
• Use a suitable polishing solution to restore the original luster of the blade.
• Handle your knives with care and avoid using detergents or other rough cleaners that can damage the surface of the blade.

Conclusion

Rust’s a natural process that occurs when iron reacts with oxygen and moisture.  It speeds up when there are impurities like salt in the environment. Prevent it by storing knives in a dry place, using oil to protect the surface, and cleaning them regularly with a mild detergent. 

So don’t worry, you can still enjoy your favorite knife set!  Just remember to use a sharp knife!

Check out our new cookbook

Bitemybun's family recipes with complete meal planner and recipe guide.

Try it out for free with Kindle Unlimited:

Read for free

Joost Nusselder, the founder of Bite My Bun is a content marketer, dad and loves trying out new food with Japanese food at the heart of his passion, and together with his team he's been creating in-depth blog articles since 2016 to help loyal readers with recipes and cooking tips.