Kouki Blue2 Kurouchi Petty 135mm

A petty knife is a small Japanese utility knife, typically with a blade between 120mm and 180mm, designed for precision tasks like peeling, trimming, and slicing fruits and vegetables. You need one when your main chef’s knife feels too large for detail work, think deveining shrimp, cutting garnishes, or any in-hand peeling where a bigger blade gets in the way. Its slightly longer and slimmer profile than a Western paring knife gives you more control for intricate cuts without sacrificing the nimble feel you want for small jobs. If you regularly find yourself reaching for a smaller blade for finishing work, a petty fills that gap cleanly.

A petty is not a replacement for a gyuto or santoku. It lacks the blade length and belly for efficient chopping, rocking, or breaking down larger proteins. If your work is mostly bulk prep, like dicing onions or slicing roasts, a petty will feel slow and underpowered. It also won’t handle heavy tasks like splitting bones or prying, so treat it as a precision tool, not an all-rounder.

The petty’s role in a Japanese kitchen is as the smaller counterpart to the gyuto, built for tasks where a full-size blade is clumsy. At Knives and Stones, the petty category covers a range of steels including VG10, White#2, Swedish Steel, VG5, SG2, and MV, from makers like Sakai Takayuki, Masamoto Sohonten, Ryusen, Nigara, Hatsukokoro, and Sentan. Most are double-beveled, and the blade length runs from 120mm to 180mm, which is what gives it that balance of reach and precision. For more on how this fits into your knife kit, see the Knives and Stones Education Centre.

Petty knife lengths vary by maker: KAI's guide defines a petty (ペティナイフ) as a small knife with a narrow blade measuring 150 mm or under. Its table gives 90 to 150 mm, and it describes the shape as a smaller gyuto with a pointed tip.

We list petty knives from 70 mm to 165 mm, including lengths above the limit used in KAI's guide.

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.