Corrosion vs. Oxidation

We dislike the knife when we see rust and metal falling off of it. Also, the blue and white spots are not pleasing. What causes these? Well, Japanese knives are typically made of high-carbon or stainless steel, both of which are prone to corrosion and oxidation. The difference between corrosion and oxidation on Japanese knives can affect their appearance, performance, and lifespan. 

Corrosion on Japanese knives refers to the breakdown or falling apart of the rusted metal due to chemical reactions with moisture, acids, salts, or other environmental factors. It can cause pitting, rust, discoloration, and even structural damage to the knife.

Oxidation on Japanese knives refers to the reaction of the metal with oxygen in the air, which can cause a patina or a layer of rust to form on the surface of the knife. While some chefs may appreciate the unique color and texture of an oxidized Japanese knife, oxidation can affect the sharpness, durability, and hygiene of the knife. Oxidation can be prevented or minimized by wiping the knife dry after each use and applying a light coating of food-grade mineral oil or wax to the blade.

Corrosion on a Japanese knife

Corrosion on a Japanese knife can take various forms, depending on the severity and type of corrosion. In general, corrosion on a Japanese knife appears as discoloration or pitting on the surface of the blade. The following are some common types of corrosion that may be seen on a Japanese knife:

1. Red or brown rust

   This common form of corrosion appears as a red or brown discoloration on the blade. Rust can be caused by exposure to moisture, salt, or acidic substances.

2. White spots or powdery residue

   This type of corrosion appears as white spots or powdery residue on the blade, often caused by exposure to salt or alkaline substances.

3. Black or gray discoloration

   This type of corrosion appears as black or gray discoloration on the blade, often caused by exposure to acids or high temperatures.

4. Pitting

   This type of corrosion appears as small pits or holes on the surface of the blade and is often caused by exposure to salt or acidic substances.

It's important to note that corrosion on a Japanese knife can affect its appearance, performance, and hygiene. Therefore, taking good care of your Japanese knife is recommended by keeping it clean, dry, and protected from moisture and acidic substances.

Oxidation on Japanese Knife

Oxidation on a Japanese knife can give the blade a unique color and texture, but it can also affect the performance, durability, and hygiene of the knife. Oxidation on a Japanese knife typically appears as a patina or a layer of rust-like discoloration on the surface of the blade. The following are some common types of oxidation that may be seen on a Japanese knife:

1. Blue or gray patina

   This type of oxidation appears as a blue or grayish patina on the blade, often caused by exposure to oxygen and humidity. Some chefs may appreciate the aesthetic appeal of a blue patina, but it can also affect the sharpness and hygiene of the knife.

2. Brown or black spots

   This type of oxidation is often caused by exposure to acidic substances or prolonged use without cleaning.

3. Rust-like discoloration

   This type of oxidation appears as rust-like discoloration on the blade, often caused by exposure to moisture, salt, or acidic substances. Rust can affect the structural integrity and hygiene of the knife if left unchecked.

It's important to note that some chefs may intentionally encourage oxidation on their Japanese knives for aesthetic or functional reasons, such as improving the knife's ability to slice or reducing the risk of food sticking to the blade. However, excessive or uncontrolled oxidation can negatively affect the knife's performance and lifespan. Therefore, it's recommended to maintain a balance between the desired level of oxidation and the proper care and maintenance of the knife.

In summary, corrosion and oxidation on Japanese knives can affect the knife's quality and longevity. Still, they are caused by different chemical reactions and can be prevented or mitigated by various care and maintenance methods.