Masamoto Sohonten Honyaki (Blue 2, 玉青鋼) Yanagiba 270 mm

A yanagiba (柳刃包丁) is a sashimi knife for slicing raw fish. A knife maker's guide says a sashimi knife cuts without breaking the fibres of the flesh, and that it is longer and narrower than other knives because slicing sashimi with crisp edges needs the length.

The whole length goes through one pulling cut. The Sakai cutlery association calls the yanagiba the sashimi knife used mainly in the Kansai region.

Size a yanagiba to the fish you prepare: a knife maker's guide gives 270 to 360 mm for professional use and 240 to 270 mm for home use, with 270 mm at home if you slice larger fish.

The guide says the whole length goes through one pulling cut, so do not choose too short a knife, and at home it points to the size of your board and your work space. We list the yanagiba (柳刃) from 210 to 360 mm, some made for left-handed use.

No. The Sakai cutlery association describes the yanagiba (柳刃包丁) edge as so acute that it cannot be used on hard things such as bones.

For bones the association describes the deba (出刃包丁), whose heel is used to hit them.

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.

No. Masamoto Sohonten's own history page says Tsukiji Masamoto set up business independently in 1951. Its products and company organisation differ completely from the Sohonten house, and the MASAMOTO trademark is a registered trademark of Masamoto Sohonten, based in Azumabashi.

Both names carry Masamoto, so check which house made the knife: Masamoto Sohonten is the Azumabashi house in Tokyo, and Tsukiji Masamoto is a separate company.

The Masamoto Sohonten history page dates the start of the house to 1866, when the founder returned home and began making cooking knives in Osawa. It says the house was first in the Kanto region to manufacture and sell genuine tempered blade cooking knives in 1874, and it opened in present-day Azumabashi, Sumida-ku, Tokyo in 1890.

The MASAMOTO trademark, No. 20269, was registered in 1903. The history page lists six generations, from the founder Minosuke Matsuzawa to Masahiro Hirano.