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Rust on your knives is not only unsightly, but if left untreated, it can cause damage to the blade. Rust damage can weaken the structural integrity of the steel and permanently damage your expensive Japanese knife. We will demonstrate how to remove rust spots from your Japanese knife and how you can prevent it from happening again.
Follow these 5 basic steps to remove rust from your Japanese knife.
- Clean the knife.
- Use the potato method, the onion method, the vinegar method, or the baking soda method to remove the rust.
- Rinse in warm soapy water.
- Dry the knife thoroughly.
- Oil the knife blade and store it appropriately.
Every knife in your kitchen is susceptible to rust, but some are more prone to this than others. With some knives in your kitchen, a little rust spot here and there may not concern you, but for your more expensive knives, you should address the rust issue promptly. Prevention of rust on your Japanese knives is always preferable to the cure!
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Can Japanese Knives Rust?
Many people are under the misconception that stainless steel knives are immune to rust. The reality, however, is that all steels can rust, but the process with some steels is slower than with others.
Japanese knives can rust and will rust if they are not cared for correctly. Most Japanese kitchen knives are not made from stainless steel but from high-carbon Japanese steel, which is not rust-resistant. Japanese knives must be well cared for to prevent rusting of the blade.
Stainless steel contains iron and carbon like most other knife steels and contains anywhere from 12 to 30% Chromium. Stainless steel also contains Manganese and Nickel, but the Chromium component in stainless steel enhances its rust resistance.
Some Japanese knives are made from stainless steel, and some are made with a Japanese steel core but clad in stainless steel to help increase the rust resistance of the knife. Traditional Japanese knives do not use stainless steel but only high-carbon Japanese steel.
If you proudly own a Japanese knife, made in the traditional way from pure Japanese high carbon steel, you have a knife that will out-perform most other knives in your kitchen, but it will rust!
Why Does Japanese Steel Rust?
Steel is formed when iron is combined with carbon in specific ratios. Iron by itself is a relatively soft material. The addition of carbon to the composition of iron significantly strengthens the iron and makes it exponentially harder than iron.
Japanese steel rusts when the iron in the steel reacts with water, or moisture-laden air, to produce iron oxide, known as rust. This chemical reaction is corrosive, destroying the iron in the production of iron oxide. Rust will consume all the iron if left unchecked, destroying the steel.
All steels contain small traces of compounds other than carbon and iron, which gives the steel its defining characteristics. The other components can include Magnesium, Nickel, Molybdenum, and low levels of Chromium.
Any steel with Chromium levels under 11% will not benefit from the rust resistance offered by this material. Japanese steel is high-quality, high-carbon steel that does not contain Chromium above a level of 11%.
The ratios of the other components in Japanese steels give it its unique characteristics to provide steels that can be hardened to high levels, increasing edge retention and strength. However, this low Chromium level in Japanese steel makes it susceptible to rust.
Is It Normal For Japanese Knives To Rust?
The superior quality of Japanese knives and the higher cost of these knives leads some people to believe that these knives should be rust-resistant as part of their higher quality.
Unfortunately, the characteristics of the steel that makes it superior for the function of the knives also make the knives less rust-resistant.
It is normal for Japanese knives to rust because of the composition of the steel. The steel composition in Japanese knives gives them superior qualities as a kitchen knife and what makes them susceptible to rust. Thus, a higher level of maintenance is required for these knives.
During your ownership of a Japanese knife, you will find some rust spots on the knife. What is your best course of action when you discover this blight on your treasured Japanese blade?
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How To Remove Rust From A Japanese Knife
If you notice rust beginning to develop on your Japanese knife, it is important to address the problem early before it damages the steel.
There are several methods you can use to remove the rust from your Japanese knife. The rust removal method you use will depend on how bad the rust problem is on the blade.
Small spots of rust can be removed with less aggressive treatments, while more established rust will require some more extreme measures.
We will begin with the methods to remove light rust, using materials you can generally find in your kitchen before covering the methods needed to remove heavier rust problems on the blade.
Using A Potato To Remove Rust From A Japanese Knife
If the rust on your knife is a few small spots and can be considered light rust, you can use the potato method to remove the rust.
You will need the following items to perform rust removal with a potato.
- 1 x potato
- Dishwashing soap or baking soda
- A clean cloth
- Mineral oil
Cut the potato in half and rub some dishwashing soap on the cut surface of the potato. Rub the cut edge of the potato over the rust spots on the knife.
Potatoes contain a weak acid called oxalic acid, which helps dissolve the rust on the surface of the metal.
If the rust spots are a little more stubborn, then sprinkle a little baking soda on the cut end of the potato after you have subbed some dishwashing liquid on the surface.
The baking soda performs as a light abrasive material to remove the rust. You can also use some fine table salt instead of baking soda.
After rubbing the blade with the potato, wash it in warm soapy water and dry it off thoroughly with a clean, dry cloth.
Apply a light film of food-grade mineral oil to the blade as a protective layer to prevent the blade from rusting.
Use An Onion To Remove Rust From A Japanese Knife
Onions are more acidic than potatoes and can be used on light rust spots that the potato method could not clean.
Cut the onion in half horizontally and rub the cut side of the onion over the rust spots on the knife. You can apply some pressure to the motion to work the onions acid deep into the rust.
It is best to position the knife blade flat on a cutting board while rubbing the onion across its surface. This is safer than trying to rub an onion on a blade you are holding freehand.
If the rust spots are not coming off easily, sprinkle a little fine table salt on the cut edge of the onion to act as a light abrasive. Use less pressure when using the salt on the onion to avoid scratching the metal.
Once the rust has been removed, wash the knife in warm soapy water and dry the blade carefully and thoroughly with a soft, dry cloth. Once again, apply oil to the blade to protect it from moisture and store the knife.
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Use Vinegar To Remove Rust From A Japanese Knife
White vinegar can act as a rust remover to address larger and deeper rust spots on your Japanese knife. White vinegar is the choice for rust removal because of its higher acetic acid content.
To use vinegar to clean the rust from your knife, you will need the following items.
- White vinegar
- A tall glass
- A light kitchen scouring pad
- Soapy water
- A clean, dry cloth
- Oil for the knife
The glass must be tall enough for the blade to stand safely in the glass. Stand the knife in the glass and pour white vinegar into the glass until all the rust spots are covered. Let the knife stand in the vinegar for no longer than 5-minutes.
If you leave the knife in the vinegar too long, the acidity in the vinegar can stain the steel and damage the steel by causing pitting where the acid eats the steel away.
After the 5-minute soak, remove the knife from the vinegar and lightly scrub rust areas that still remain with the kitchen scouring pad.
Rinse the knife in warm soapy water to neutralize the acidity and wash the vinegar from the blade. Dry the knife completely with a clean, dry cloth.
After drying the knife, apply a light coat of oil to protect the knife from beginning to rust again. You should use a food-safe oil such as food-grade mineral oil on any knives used to prepare food.
Using Baking Soda to Remove Rust From A Japanese Knife
Another method of removing rust from your Japanese knife is to use baking soda as a light abrasive to scrub the rust away. To use the baking soda in this way, you will need to gather the following items together.
- Baking soda
- A toothbrush
- A clean, damp cloth
- Warm soapy water
- Dry cloth
Place a tablespoon of baking soda onto a small plate and pour a little water into the baking soda. Use the toothbrush to mix the water and baking soda into a thick paste.
Scoop up some of the paste with the toothbrush and gently scrub the rust spots on the knife’s blade using a circular motion. The light abrasive characteristics of the baking soda will remove the rust from the metal’s surface.
As the rust comes off the knife, you will see the color of the paste change to a rusty red color. Wipe the paste off the knife with the damp cloth and inspect the knife for rust. If the rust still persists, use some more paste and continue to scrub the area.
On more stubborn spots, you can place a drop of lemon juice on the rust spot, scrub it with the toothbrush to loosen the rust, and then apply more paste and scrub again.
Once the rust is gone, rinse the knife in warm soapy water and thoroughly dry the knife with a clean, dry cloth. Oil the knife to prevent rust from developing again and store the knife safely.
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Remove Rust From Your Japanese Knife With A Rust Eraser
A rust eraser is a stretchable plastic or rubber combined with fine, abrasive compounds that remove rust from the surface or the knife.
Rust erasers (Amazon link) are more abrasive than the other methods discussed and will leave scratches on the blade. Consequently, when using a rust eraser on your Japanese knife, always make sure you use the rust eraser in the same direction as the existing scratch pattern on the knife.
Rust erasers will remove rust and remove stains and patina and restore the look of the knife. The erasers usually come in two grits, medium grit and fine grit. The grit level you use will depend on the amount of rust on the knife.
To use the rust eraser, place the knife’s blade on a firm surface, such as on top of a kitchen towel on the counter-top edge. Wet the eraser with water and gently rub it on the blade, following the same direction as the existing scratch pattern on the knife.
After cleaning the rust from the blade with the eraser, wash the knife in warm soapy water, dry the blade and apply a thin layer of food-safe oil to prevent rust from starting again.
How To Prevent A Japanese Knife From Rusting?
If you own any knives that are not stainless steel, you will know that rust can develop on these blades very quickly. All it takes is one occasion where the knife was not cleaned or washed properly, and the rust will start to appear.
The best way to keep your Japanese knives rust-free is to take good care of them when you use them and store them.
Follow these simple knife-care steps to keep your Japanese knives rust-free.
- Never let your knife air-dry.
You should never wash your high-carbon steel knives and then place them in the drying rack to air-dry. You should always wipe them dry with a soft, dry cloth.
- Do not wash your Japanese knife in a dishwasher.
Washing your knife in a dishwasher will promote the development of rust and damage the knife’s cutting edge and damage the wooden handle.
- Wash the knife immediately after use.
Do not allow the knife to sit on the counter after using it, especially after cutting acidic ingredients or with high moisture content. This will allow the rust to start on the knife within minutes.
- Oil the knife after washing and when storing the knife.
Use a food-safe oil such as food-grade mineral oil and cover the blade with a thin layer after washing and drying the knife. The mineral oil will act as a barrier between the steel and moisture in the air, preventing rust from starting.
- When you notice rust, remove it as soon as possible.
Even when taking steps to prevent rust, it can still find a way to contaminate your blade. As soon as you notice the rust beginning, address the problem and remove the rust.
BTW: If you want to know more about Japanese and other knives and their sharpening, check out the books listed above. These books are recommended by professional sharpeners and knife makers (Amazon links):
- Japanese Kitchen Knives: Essential Techniques and Recipes
- The Knifenerd Guide to Japanese Knives
- Knife: The Culture, Craft, and Cult of the Cook’s Knife
- Sharp: The Definitive Introduction to Knives, Sharpening, and Cutting Techniques, with Recipes from Great Chefs
Rust is one of the downsides to high-carbon steel blades, but the advantages this steel gives to Japanese knives are worth the additional effort to take care of them.
If you get into a good, disciplined cleaning and maintenance routine with your Japanese knives, you will have little cause for concern for a major rust problem.
Keep your knives clean and dry and address rust spots immediately when you notice them, and your Japanese knife will give you many years of faithful service!
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