How to Care for and Sharpen a Japanese Knife: Rust, Washing and Whetstones

You cook dinner, rinse the plates, and leave your new carbon steel knife on the board for the night. In the morning there is an orange bloom along the edge. Did you ruin it?

Probably not. Kiya (木屋), the Tokyo knife house, says plainly that rust on a carbon steel knife is something that cannot be completely prevented, and that it appears most often when the knife is new. What you can control is how fast you deal with it. Most of the care below follows from one question: is your blade stainless or carbon steel?

This guide draws on Japanese makers and shops, mainly Kai (貝印), Nihonbashi Kiya (日本橋木屋) and Tsukiji Aritsugu (築地有次), and we have not tested the methods ourselves. If you are still choosing a knife, start with gyuto, santoku and bunka knives compared.

Know your steel

Check the product page or box. The two behave quite differently.

	Stainless steel	Carbon steel (hagane, 鋼)
Rust	Rust-resistant, but can still rust slightly	Rusts easily; without an anti-rust treatment it will rust (Aritsugu)
Care	Does not need frequent care	Needs care after every use
Dishwasher	Only if all-stainless or labelled dishwasher-safe	Never

By Kai’s and Kiya’s figures, stainless is carbon steel with about 13-15% chromium added to resist rust, while carbon steel is iron with about 0.6-1.2% carbon. Kai describes carbon steel as very easy to rust, but also as cutting well and easy to sharpen. That is the trade-off for the extra care. Many Japanese knives also join a hard steel edge to a softer body. Kai groups these clad knives with carbon steel when it warns about fast rusting, so treat a clad knife with a carbon edge like a carbon steel one.

The daily routine

Kai warns that carbon steel and clad knives can rust in around 10 minutes if moisture or food residue stays on them. So the routine is short but should not be skipped.

1. Rinse between ingredients. Zwilling’s Japanese site suggests washing the knife and wiping off water as you move from one ingredient to the next.
2. Wash at once after salty or acidic food with dish detergent.
3. Wash by hand. Use mild detergent, press the knife against the cutting board and scrub it with a sponge, then rinse. Pouring hot water over the blade sanitises it and helps the water evaporate.
4. Dry completely. Wipe with a dry cloth, then let it air-dry until no moisture is left.
5. Store it dry. For long storage, wrap the dry knife in newspaper and keep it somewhere ventilated with little humidity.

Technique matters too. Kai explains that chips come from forces that bend the edge, such as prying or twisting the blade, so move the knife straight forwards and backwards.

When rust appears

Kiya’s method for light rust on a carbon steel knife is pleasantly low-tech: wet the knife, sprinkle powdered cleanser on the rust, rub it off with a damp wine cork, then rinse and dry thoroughly with a dry towel.

Repeat this over time, Kiya says, and the blade rusts less and becomes more stable. For heavier rust, Kai lists a coarse whetstone (#300-400) as the tool.

Do I need a whetstone?

Probably, if you want to keep a good knife sharp. A whetstone (toishi, 砥石) is graded by number, and a lower number means a coarser stone. Kai sorts them into three groups.

Stone	Japanese	Grit	Use
Coarse	ara-toishi (荒砥石)	#300-400	Repairing chips, removing rust
Medium	naka-toishi (中砥石)	#800-1000	Routine sharpening
Finishing	shiage-toishi (仕上げ砥石)	#2000-3000	Refining the edge

You may think you need all three. Kai’s answer is that a medium stone is enough for everyday resharpening, about once or twice a month. Only a chipped or badly worn edge needs the full sequence.

What about the pull-through sharpener in the kitchen drawer? Kai says repeated use wears down only the very tip, so the knife struggles to regain its sharpness. A whetstone rod or file rod does not put an edge on the knife either: it removes grease and dirt and restores sharpness only temporarily.

Two habits help. Kai says to soak a stone until it stops releasing bubbles, and Kiya suggests resting it on a damp cloth to hold it still. For a gyuto or santoku, Kiya’s guide turns the knife to about 50 degrees across the stone. That is the direction the knife points, not its tilt: the spine is raised only a little off the stone.

The back of a single-edged knife

Single-edged knives, such as the deba and yanagiba, have one trap when you sharpen them: the back. Kiya advises laying the back (ura, 裏) flat against the stone. Sakai Ichimonji Mitsuhide (堺一文字光秀) explains that the urasuki (裏スキ) hollow stays clear of the stone, so only the rims at the edge and the spine touch during this back honing (ura-oshi, 裏押し). It also warns that the back of a Japanese knife is bare steel, and that over-sharpening it wears away the hollow and the steel. Its advice is to hone the back with light pressure and not to overdo it. Our guide to the types of Japanese knives shows why the back is hollowed in the first place.

If you would rather learn in person, Sanjo Kaji Dojo (三条鍛冶道場) in Niigata lists knife sharpening among its hands-on experiences. In our view, a lesson like that can help with routine care at home, but for a knife you value, a professional sharpener is still the right call. See knife-making experiences in Japan for more.

When to hand it to a professional

In Sakai (堺), the city explains that forging, edge sharpening (hatsuke, 刃付け) and handle fitting are each done by separate specialists. Sharpening is a trade of its own, which is worth remembering when you see the price and the wait.

Where	What is offered	Notes
Nihonbashi Kiya (Tokyo)	Resharpening, only for knives Kiya sells	Japanese-style ¥2,200-5,500, Western-style ¥1,650-6,050 (tax included); about 3 weeks. Large chips may cost 50% or more extra
Sakai Denshokan (堺伝匠館), Sakai	Resharpening of knives and scissors	From ¥1,600, shipping extra. Sharpening is done at weekends and can take about a week. Its page does not say whether it takes knives bought elsewhere

Prices are as listed on each official page when checked on 28 October 2026, and may change. Check the official page before you plan around them.

The Gifu tourism site also lists resharpening by craftspeople at Gifu Seki Hamono Kaikan (岐阜関刃物会館) in Seki. We could not confirm anything beyond that line: no price, and no word on whether it takes knives from other makers or by post.

Start with the shop that sold you the knife. Kiya accepts only knives it sells, so check its official page or ask the shop whether yours is covered. Kiya’s page asks you to contact the shop before posting a knife and to pay the shipping, and Sakai Denshokan’s page asks that postal requests be discussed separately. Neither says whether it takes knives from overseas or handles English, so we do not recommend posting a knife to Japan. If you are visiting Japan, ask the shop where you bought your knife whether it can take the knife in person, bearing in mind the waits above.

Before the next dinner

The orange bloom is a nuisance, not a verdict on the knife. Next time, wash and dry it as soon as you have finished cutting, then put it away, and you have done what the makers above ask.