Why do knives dull without use?

By | November 11, 2023

In the world of cooking, having a sharp knife is super important. But here’s a puzzle: many cooking enthusiasts and professionals find their knives getting dull over time, even when they’re not being used much. This article is like a detective mission – we’re going to uncover why this happens. We’ll dig into things like oxidation, moisture, chemical reactions, microscopic wear, atomic migration, and the kind of materials knives are made of. Plus, we’re not just solving the mystery; we’re also giving you practical advice on picking knives that stay sharp and the right ways to keep them that way.


Oxidation: The Quiet Culprit

Rusty (oxidation) knife

Oxidation, a natural happening, takes place when the metal in knife blades reacts with the air’s oxygen, forming rust on the blade’s surface.

Rust is a powdery substance that can gather on the edge of a knife, making it hard to cut things.

Even stainless steel, known for resisting rust, can’t avoid this problem.

It’s important to understand oxidation details to stop or lessen its impact. Things like the metal type and the environment affect how fast and strong this process is. To fight oxidation and keep a sharp knife, make sure to clean, dry, and put a little bit of oil on the blade regularly.

If your knife gets rusty, you can fix it by soaking the blade in a mild acid like vinegar or lemon juice for a few minutes. Then, gently scrub the blade with a soft brush, rinse it with water, and dry it right away. This will bring your knife back to its sharp self.


Moisture: The Covert Adversary


Moisture, whether in the form of ambient humidity or direct contact with liquids, hastens the corrosion of knife blades. Water sets off a corrosive process that gradually erodes the blade’s sharp edge.

Moisture can encourage the growth of bacteria and mold, leading to blade corrosion for several reasons:

Acid Production: Bacteria and mold generate acids that corrode the blade’s metal, weakening it and making it more prone to dulling.

Biofilm Formation: Bacteria and mold can form a biofilm on the blade’s surface, trapping moisture and creating an environment conducive to corrosion.

Chemical Release: Bacteria and mold release chemicals that react with the metal, causing corrosion.

Moreover, moisture can directly react with the metal of the blade, especially in the case of high-carbon steels, which are particularly susceptible to corrosion.

Ensuring proper drying after each use and before storage is crucial to counteract the effects of moisture. Additionally, storing knives in a cool and dry environment, away from the kitchen sink or dishwasher, helps alleviate the impact of humidity. Opting for knives with corrosion-resistant materials, such as high-quality stainless steel or ceramic, adds an extra layer of defense against moisture-induced dullness.


Chemical Reactions: Culinary Alchemy at Work

Chemical corrosion on knife surface

In the kitchen, knives frequently encounter various foods containing acidic or alkaline substances, triggering chemical reactions that gradually alter the blade’s composition, resulting in dullness over time.

Acid corrosion: This is a chemical reaction between metal and acid, with acids present in a variety of foods like lemons, limes, tomatoes, and vinegar. When a knife blade interacts with an acid, the acid reacts with the metal, causing corrosion.

Alkali corrosion: Alkali corrosion is another chemical reaction, this time between metal and an alkali. Alkalis, found in household products like bleach, oven cleaner, and drain cleaner, can react with the metal of a knife blade, leading to corrosion.

Understanding the specifics of these chemical interactions is crucial for effective knife maintenance. Regular cleaning and prompt drying after cutting acidic foods, such as tomatoes or citrus fruits, can minimize the impact of these reactions. Additionally, opting for knives with materials less susceptible to chemical reactivity, such as high-quality stainless steel or ceramic, offers a proactive solution to counteract this dullness factor.


Microscopic Wear: The Unseen Erosion

Magnified Blade Edge

Microscopic wear refers to subtle abrasions occurring on a blade’s surface over time, even in the absence of visible use. Factors such as vibrations, temperature changes, and incidental contact with surfaces contribute to this wear.

Vibrations can cause atoms in the steel to move and collide, eventually leading to the formation of microcracks. These microcracks can grow, causing the blade’s edge to become rounded and dull.

Temperature changes can also cause the steel in the blade to expand and contract, creating stress and contributing to microscopic wear. For instance, storing knives in a hot, humid environment can lead to steel expansion and contraction, putting stress on the material and causing microscopic wear.

Incidental contact with surfaces can also induce microscopic wear on a knife blade. For example, if you accidentally bump your knife against a hard surface like a countertop or sink, the impact can cause microscopic wear on the blade’s edge.

While microscopic, the cumulative effect of these abrasions can significantly impact the blade’s sharpness. Choosing knives with high-quality and durable materials, along with proper cutting surfaces, can minimize microscopic wear. Regular honing, aligning the blade’s edge, also helps mitigate wear effects, preserving the knife’s sharpness over an extended period.


Atomic Migration: The Inevitable Edge Deterioration

atomic migration

The concept of atomic migration challenges the assumption that a knife’s edge can remain perpetually sharp. Over time, the movement of atoms within the blade contributes to the natural degradation of the sharp edge.

Atomic migration is the process by which atoms at the edge of a knife blade gradually move away over time.

Several factors, including stress, heat, and vibration, can cause this phenomenon.

Initially, it leads to the rounding of the blade’s edge because the atoms at the edge are under significant stress. As time passes, these atoms migrate away from the edge, resulting in a rounded and dull appearance.

Additionally, atomic migration can cause the blade’s edge to become uneven. The non-uniform movement of atoms at the edge can create areas that are duller than others.

The rate of atomic migration is influenced by factors such as the type of steel used in the knife, the heat treatment process undergone by the knife, and the knife’s usage. For instance, knives made with high-carbon steels are more prone to atomic migration than those made with stainless steels.

While this inherent process is unavoidable, highlighting the finite lifespan of an ultra-sharp edge, understanding its inevitability allows users to set realistic expectations for a knife’s performance and longevity. Regular maintenance practices, such as honing and occasional sharpening, can help counteract the effects of atomic migration, extending the usable life of the knife.


Choosing Knives that Resist Dullness


The material of a knife plays a crucial role in determining its susceptibility to dullness, even during periods of inactivity. Various factors associated with the material contribute to the phenomenon of knives losing their edge over time, even without frequent use.


a) Oxidation and Corrosion:

Stainless vs. Carbon Steel: Stainless steel exhibits greater resistance to oxidation and corrosion compared to carbon steel. While carbon steel knives are renowned for their sharpness, they are more susceptible to rust and corrosion, especially in high humidity or acidic environments, leading to the development of a dull outer layer due to oxidation.


b) Carbide Formation and Composition:

High vs. Low Carbide Content: Carbides, rigid compounds forming within the metal matrix of a knife, significantly influence its characteristics. A high carbide content enhances hardness and edge retention but may increase vulnerability to corrosion. Conversely, materials with lower carbide content may not maintain their edge as long but generally boast greater corrosion resistance.


c) Heat Treatment:

Hardness and Resilience: The heat treatment process during manufacturing impacts the knife’s hardness and resilience. Harder knives, often measured on the Rockwell Hardness Scale (HRC), tend to retain sharpness for longer durations. However, excessive hardness can render knives more brittle and susceptible to chipping.


d) Microstructure and Crystal Arrangement:

Fine vs. Coarse Grains: The microstructure of the metal, influenced by grain size and arrangement, plays a pivotal role in edge retention. Finer grain structures are generally linked to superior edge retention, while coarse grains may contribute to quicker dulling.


e) Presence of Alloying Elements:

Impact of Elements like Vanadium: Alloying elements such as vanadium can contribute to carbide formation and heightened hardness. However, an excess of certain elements may increase susceptibility to corrosion. The overall alloy composition crucially determines the delicate balance between sharpness and corrosion resistance.


f) Sensitivity to Environmental Factors:

Stainless Steel Varieties: Different varieties of stainless steel exhibit varying levels of resistance to environmental factors. Some varieties are more resistant to moisture and acidic substances, reducing the likelihood of dullness during periods of inactivity.


g) Surface Finish and Treatment:

Polished vs. Rough Surfaces: The surface finish of the blade significantly affects its susceptibility to corrosion. A polished surface generally offers more resistance to corrosion than a rough or pitted surface, thereby reducing the likelihood of dullness over time.


Table of knives selection guide



So, in a nutshell, knives getting dull without even using them a lot is a bit like solving a puzzle. We found out it’s because of things like rust, water, chemicals, tiny scratches, atoms moving around, and the kind of stuff knives are made of. Now, the cool part is that if you understand these things, you can be like a superhero for your knives. Picking the right material, storing them properly, and giving them a little honing and sharpening regularly – these are like the secret moves to keep your knives super sharp. By figuring out why knives get dull, both kitchen enthusiasts and pros can make sure their knives stay sharp and ready for action!

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