Sukenari Blue 2 K-tip Yanagiba 270mm, Ebony Brass Handle

Yes, carbon steels such as Aogami (Blue) and Shirogami (White) react with food, moisture, and acids, so left wet they can spot or rust. With normal use they develop a grey, blue and brown patina, and that patina is expected on a carbon knife rather than damage.

Aogami has only a little chromium, far below what a stainless steel needs, so water left sitting on the blade will spot it. A patina is a stable oxide layer that slows rust down; orange or red specks are rust.

Care is simple once it becomes habit:

• Wipe the blade as you go, especially after onion, citrus or tomato.
• When you finish, wash it in warm water with a little soap and dry it straight away with a towel. Don't let it air dry or leave it in the sink or the dish rack, and never put it in the dishwasher.
• Store it dry: on a magnetic strip, in a saya or in a block in a dry spot.
• If it's going to sit unused for a while, wipe on a thin film of food-safe mineral oil before storing it.

If you do find rust, lift light orange spots with a rust eraser and a little water, then dry and oil the blade. We stock the CKK and Naniwa rust erasers, and the Koyo Sunlite Polishing Paste (Blue for Steel) lifts light surface rust or refreshes a finish. Rust on the edge itself comes off the next time you sharpen. Deep pitting needs a professional sharpener. Avoid steel wool and harsh scouring on a polished or kurouchi finish, because they scratch it.

On a stainless-clad knife only the thin line of carbon steel along the edge can rust; the cladding stays clean. A carbon-clad or honyaki blade can rust over its whole face and needs the same care all over.

Carbon steel rewards this small amount of attention with a keener edge and easier sharpening than most stainless.

Proterial lists 1.05 to 1.15% carbon for both steels; its Blue 2 table lists 0.20 to 0.50% chromium and 1.00 to 1.50% tungsten, while its White 2 table lists neither.

Proterial describes White 2 as a carbon steel with minimum impurities and high hardness, and Blue 2 as an alloy steel with tungsten and chromium to improve heat-treatment properties and wear resistance, with a hardening hardness of over 60 HRC for both. Neither steel is close to the JSSA's 10.5% minimum for stainless.

Sukenari's own site carries both names together, titled the official site of 株式会社スケナリ with 佑成 named as a registered trademark. 佑成 is the house mark that appears on the blades.

So one house answers to both names: Sukenari is the company, 株式会社スケナリ, working from Fuchu machi in Toyama City, and 佑成 is its mark on the steel.

Yes. Sukenari says its knives are made by craftsmen by hand, one at a time, at its workshop in Fuchu machi, Toyama City.

The Sukenari lines we stock carry the workshop name in their titles.

The workshop says the 佑 of its registered mark 佑成 (read Sukenari) is written with the person radical and 右, right, and that the character carries the wish for its tools to become the cook's indispensable right arm.

The company's own site title reads 登録商標 佑成 (registered trademark), and 佑成 is the house mark on its blades.