Japanese knives: why they stain and how to maintain them

Couteaux japonais pourquoi ils changent de couleur et comment les entretenir

All owners of Japanese knives know that good maintenance is necessary to keep their knife beautiful and efficient over time. A very important factor to consider is the risk of oxidation.
Despite a large number of users rejecting oxidizable blades. It is important to know how to analyze the behavior of steel to distinguish beneficial and necessary oxidation for the blade from poor oxidation that can lead to the formation of rust.

The types of steels used in Japanese cutlery

In Japanese cutlery, the steels used can be divided into two main categories, steels resistant to oxidation, or stainless steels, and oxidizable steels. Some people sometimes refer to oxidizable steels as “high carbon steel”, but this definition is incorrect because Japanese stainless steels are also high carbon steels. The main factor that makes a steel stainless is due to the presence of Chromium (Cr) in its alloy. Any steel having in its alloy a chromium rate equal to or greater than 12%, will be considered as steel resistant to oxidation or stainless.

Steels that do not have a sufficiently high rate, such as Aogami or Shirogami steel, are steels that react to the acidity and salinity of food, or sometimes even to the humidity present in the air.

How to Distinguish Oxidation on the blade

As we use a forged non-stainless steel knife, we will notice that the blade will start to change colour. It will colour first with shades of golden yellow, then with shades of blue and magenta, and in some cases black. This color change is the Patina. It is developed naturally by the steel itself to protect itself from oxidation. It is therefore a positive aspect when your blade oxidizes and it is strongly advised to keep this patina. This particularity of oxidizable steels is very interesting because your blade will tell its history. Also, depending on the foods that are cut, the nuances of the patina will change; for example, proteins promote the development of a magnificent blue patina.

However, if you see orange spots with a tendency to dark brown, this is not a good omen. This certainly announces the beginning of rust and it will have to be removed as soon as possible. To do this, if the stain has just appeared, you can apply a few drops of lemon to the blade, wait ten seconds and then rub with the same skin of the lemon, then wash and wipe the knife. If that doesn’t work then you can rub gently with the more abrasive side of the sponge to remove it.

Tips for maintaining your blades

Prevention has always been better than cure. To promote the development of the patina and avoid rust, it is very important to wipe your knife after each use. Leaving it wet will promote the development of rust. Before storing your knife, once again, it is very important to wash it and above all to make sure that it is completely dry before storing it. As far as storage is concerned, it is best to store the knife in its box or in its case, to avoid contact with external factors, such as humidity.

Now you know how to analyze the behavior of your blade, however if you have any doubts or questions, do not hesitate to contact us.