Nakagawa Blue 1 KU Damascus Sujihiki 240mm Etched Black Ebony by Hatsukokoro

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.

Proterial, which makes both, describes each the same way: an alloy steel with tungsten and chromium added to improve heat-treatment properties and wear resistance, hardening to over 60 HRC.

Its figures give Blue 1 (青紙1号) more carbon and tungsten, 1.25 to 1.35% carbon and 1.50 to 2.00% tungsten against Blue 2's 1.05 to 1.15% and 1.00 to 1.50%, with chromium of 0.30 to 0.50% against 0.20 to 0.50%.

Yes, Satoshi Nakagawa forges those lines for the Hatsukokoro brand, and our product titles name them Hatsukokoro by Nakagawa and Hatsukokoro x Nakagawa. He works from his own company in Sakai, Nakagawa Uchihamono.

He trained for sixteen years under Kenichi Shiraki as his only disciple and successor. He forges White 3 to White 1, Blue 2 to Blue 1, stainless Ginsan, VG10 and honyaki, so the steel in each line title is part of your choice.

Pick by how much care you want to give. Ginsan is stainless, while Blue 1 and Blue 2 are carbon steels that need to be dried and oiled after use.

If you will dry and oil the blade after each use, a Blue 1 or Blue 2 line can suit you, and if you want the least fuss in a busy kitchen, Ginsan is the easier choice.