Traditional Japanese blade metallurgy centred in Sakai (Osaka), Echizen (Fukui), and Seki (Gifu); Hitachi Metals (now Proterial) in Yasugi, Shimane is the primary producer of shirogami and aogami steels; modern stainless alloys from Daido Steel (VG-10) and Kikusumi (ZDP-189)
Japanese kitchen knife metallurgy centres on a fundamental distinction between hagane (鋼, carbon steel) and stainless alloys, each carrying performance trade-offs that professional Japanese cooks navigate with deliberate intent. Hagane encompasses numerous carbon steel types: shirogami (white steel, Hitachi No. 1 and No. 2 — extremely pure, high carbon, capable of the sharpest edges but highly reactive to moisture and acids); aogami (blue steel, Hitachi No. 1 and No. 2 — carbon steel with added tungsten and chromium for edge retention, slightly less reactive than white steel); and yasugi steel variants used in traditional production. Pure carbon steel blades achieve the finest cutting edge achievable, producing the smoothest cell rupture at microscopic level — particularly prized in fish butchery where clean cells prevent oxidative damage to raw flesh. The trade-off is reactivity: carbon steel discolours, develops patina (kuro-uchi, the dark forge finish some users deliberately preserve), and can impart metallic flavour to cut acidic ingredients. Stainless steels — from basic SUS440C through premium Swedish Sandvik 13C26 (used by Global) to powdered metallurgy steels like ZDP-189 (extremely hard, capable of very fine edges with appropriate technique) — provide corrosion resistance and easier maintenance at the cost of some edge acuity and the particular 'bite' of carbon steel on a whetstone. VG-10 (Daido Steel) represents the most widely used Japanese premium stainless steel: 1% carbon, 15% chromium, plus cobalt — used in Shun and many mid-range Japanese knife brands. Clad (hagane-awase) construction, laminating a hard core steel between softer stainless outer layers, attempts to achieve both properties; the hard core takes the edge while the cladding resists corrosion on the exposed body.
Not a flavour ingredient but a precision tool — knife metallurgy affects cut quality at cellular level: carbon steel's sharper edge reduces cell rupture in fish and vegetables, minimising oxidation and preserving flavour integrity
{"Shirogami (white steel) is the purest carbon steel — finest possible edge, highest reactivity; aogami (blue steel) adds tungsten/chromium for retention","Carbon steel's reactive surface requires acid neutralisation, immediate drying, and periodic oiling to prevent rust and patina","Stainless steel provides corrosion resistance but is harder to sharpen to the same acuity as carbon steel on whetstones","VG-10 is the benchmark mid-high Japanese stainless — RC 60–62 hardness, widely accessible, responsive to whetstone work","Clad/laminated construction (hagane-awase) uses a carbon steel core between stainless layers — practical for professional environments requiring low-maintenance performance"}
{"For first-time professional purchase: aogami No. 2 offers the best edge retention among traditional steels with slightly lower reactivity than shirogami","Tsubaki oil (camellia oil) applied to carbon steel blade surface after use and drying is the traditional protective coating — food-safe and effective","ZDP-189 at RC 67–68 is extremely hard and takes an exceptional edge, but micro-chipping risk increases — requires experienced whetstone technique and is not for daily rough use","The kuro-uchi (forge scale) dark finish on some hagane knives should be preserved if possible — it provides minimal corrosion resistance and is aesthetically distinctive","When testing sharpness: slice a single sheet of paper cleanly with the blade's full length in one draw — carbon steel should do this without drag; stainless requires higher grit finish to achieve the same"}
{"Putting carbon steel knives through a dishwasher — the heat, detergent, and prolonged moisture cause immediate rust","Using high-carbon knives on acidic ingredients (lemon, tomato) without immediate rinsing and drying — acid etch develops into pitting over time","Sharpening stainless with the same angle and pressure as carbon steel — stainless requires more pressure and finer grit progression","Believing clad construction eliminates all carbon steel maintenance requirements — the exposed cutting edge is still the carbon steel core"}
The Japanese Kitchen — Hiroko Shimbo; An Edge in the Kitchen — Chad Ward