Teruyasu Fujiwara Denka Sujihiki 240mm Aogami Super Kurouchi

Between 210 and 270 mm, depending on where it will work. One Japanese maker lists 210 to 240 mm, double-bevel, for home use and 240 to 270 mm, single- or double-bevel, for professional kitchens.

Another, in Sakai, recommends 240 mm at home, with the size of your board in mind, and 270 mm for professional use.

A sujihiki is a long, double-bevel knife for dividing larger pieces of meat into their parts, and its length lets it slice sashimi too; a yanagiba is the sashimi knife.

The Sakai cutlery association describes the yanagiba (柳刃包丁) edge as so acute that it cannot be used on bone or other hard things, so choose the sujihiki for meat and the yanagiba if sashimi is the main job.

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.

Aogami Blue steel, specifically Aogami Super (Blue Super), is a high-carbon Japanese knife steel made by Proterial that chefs value for its ability to take an extremely sharp edge and hold it longer than most other carbon steels, thanks to a composition with 1.40 to 1.50% carbon, 2.00 to 2.50% tungsten and 0.30 to 0.50% vanadium.

The "Blue" in Aogami refers to the color of the paper the steel is wrapped in at the mill, not the steel itself. Proterial describes Aogami Super as an alloy steel with tungsten, chromium and vanadium to improve heat-treatment properties and wear resistance. Proterial gives it a hardening hardness of over 60 HRC, giving you a blade that can be ground very thin for aggressive cutting performance while still resisting chipping in normal use. The trade-off is that, like all high-carbon steels, it is not stainless: it will rust if left wet or acidic, so you need to wipe it down and keep it dry.

Aogami (Blue) steel has less than half a percent of chromium, nowhere near what a stainless steel needs, so water left sitting on the blade will spot it. Dry it as soon as you finish, keep it somewhere dry, and let a patina build. Do that and aogami will hardly ever rust. On a stainless-clad knife only the thin line of aogami along the edge can rust; the cladding stays clean.

Will a carbon steel knife rust? covers patina, rust removal and which cladding rusts.

The difference is in Proterial's own figures: Aogami Super has 1.40 to 1.50% carbon, 2.00 to 2.50% tungsten, 0.30 to 0.50% chromium and 0.30 to 0.50% vanadium, against Aogami 2 (Blue 2) at 1.05 to 1.15% carbon, 1.00 to 1.50% tungsten and 0.20 to 0.50% chromium.

Proterial describes both as alloy steels with tungsten and chromium to improve heat-treatment properties and wear resistance, and also names vanadium for Aogami Super. Both pages list hardening hardness over 60 HRC, and Proterial lists Aogami Super for high-quality planes, other tipped tools, kitchen knives and sickles.

Fujiwara's own product page says these knives are made by sandwiching the top grade steel Aogami Super in stainless.

Fujiwara describes Aogami Super as an alloy made by adding tungsten and chromium to low-impurity White steel, developed for blades.

Yes, the carbon steel core can rust even though the outside is stainless.

The outside is stainless, according to Fujiwara's product page. The FAQ says to wipe the steel at the edge dry after use before storing it.