The Legacy of Hitachi Metals' Yasugi Steel
For most of the 20th century, the benchmark for high-carbon knife steel in Japan came from a single source: Hitachi Metals' Yasugi Steel Works in Shimane Prefecture. From this facility emerged two legendary product lines — Shirogami (White Steel) and Aogami (Blue Steel) — named after the coloured paper wrapping used to distinguish them on the factory floor. These steels remain the gold standard for traditional Japanese hocho to this day.
Shirogami: White Steel
Shirogami is an extremely pure high-carbon steel with very tight tolerances on impurities. Its purity is precisely what makes it special: a skilled blacksmith can harden it to achieve a razor-sharp edge that is virtually unmatched in its initial keenness.
Grades of White Steel
- Shirogami #1 (White #1): Higher carbon content (~1.25–1.35%). Harder, capable of reaching HRC 65+, takes an extraordinarily fine edge.
- Shirogami #2 (White #2): Slightly lower carbon (~1.05–1.15%). A touch more forgiving, slightly easier to sharpen, and very commonly used in production knives.
Characteristics
- Exceptional initial sharpness
- Relatively easy to sharpen on a whetstone — responds beautifully
- Reactive — will patina and rust without proper care
- Less edge retention than blue steel under heavy use
Aogami: Blue Steel
Aogami begins with white steel as a base but adds tungsten and chromium, which refine the grain structure and dramatically improve wear resistance. The result is a steel that holds its edge longer under heavy cutting work.
Grades of Blue Steel
- Aogami #1 (Blue #1): Higher tungsten content, very hard, excellent edge retention, preferred by professional chefs for high-volume work.
- Aogami #2 (Blue #2): The most widely used blue steel. A superb balance of sharpness, toughness, and edge retention. A favourite among serious home cooks.
- Aogami Super (Blue Super): The premium tier — adds molybdenum and vanadium for outstanding wear resistance. Can be harder to sharpen but holds an edge remarkably long.
Comparing White and Blue Steel
| Property | Shirogami (White) | Aogami (Blue) |
|---|---|---|
| Initial sharpness | Exceptional | Exceptional |
| Edge retention | Moderate | High to very high |
| Ease of sharpening | Very easy | Moderate |
| Reactivity (rust risk) | High | High (slightly less than white) |
| Best for | Precision cutting, sashimi, dedicated knife users | Heavy daily use, professional kitchens |
The Care Commitment
Both white and blue steel are reactive carbon steels — they will rust if left wet, and they will develop a patina over time from contact with acidic foods. This is not a flaw; many users consider a well-earned patina a sign of a working knife. However, it does mean you must wipe the blade dry immediately after use and apply a light coat of camellia oil if storing for any length of time.
If you're prepared to honour that commitment, the reward is a knife that feels unlike anything made from stainless steel — alive, responsive, and deeply connected to the tradition of Japanese craftsmanship.