Japanese kitchen knives can be forged using a variety of construction methods, but two of the most iconic are san mai and honyaki. While they might look similar at a glance—especially after polishing—the underlying construction significantly affects how the knife should be maintained over time.
San mai means “three layers.” A hard carbon or stainless steel core is sandwiched between two softer layers of cladding, often made of lower-carbon steel or soft stainless. This outer layer is easier to work with and offers corrosion resistance, making sharpening more forgiving and rust less of a day-to-day concern.
Most modern Japanese knives—especially those made for export—use san mai construction. It’s practical, durable, and allows manufacturers to offer carbon steel performance without fully exposing the reactive material.
Honyaki refers to knives made from a single piece of high-carbon steel that has been differentially hardened, mimicking the tradition of Japanese sword-making. There’s no cladding. No protective outer jacket. Just exposed core steel, tip to tang.
This makes honyaki knives incredibly sharp and capable of holding that edge longer than most—but at a price. Without cladding, there’s no buffer against rust, warping, or chipping. Every inch is the real deal. This makes them harder to sharpen, more reactive with food, and prone to rusting if not carefully dried and stored after each use.
In san mai knives, the edge is the only part of the knife where the core steel is exposed. That means rust, pitting, or micro-chipping is typically limited to the cutting edge—easy to address during sharpening.
In honyaki knives, the entire surface is reactive. Acidic foods, water droplets, and even humidity can leave marks or accelerate corrosion. This isn’t just cosmetic: corrosion along the face of the blade can eventually interfere with food release and lead to structural degradation.
If you want a knife that performs brilliantly and doesn’t punish you for leaving it out for 20 minutes, san mai is your friend. If you’re ready for a blade that demands as much from you as it gives, honyaki might be the summit.
Just remember: the more core steel you expose, the more it asks of you in return.
日本の包丁にはさまざまな製法がありますが、特に象徴的なのが「三枚打ち」と「本焼き」です。見た目は似ているかもしれませんが、構造の違いは日々のメンテナンスに大きな影響を与えます。
「三枚打ち」とは、硬い芯材（炭素鋼やステンレス）を、比較的柔らかい鋼材で左右から挟み込む「三層構造」です。外側のクラッド（被覆）材は錆びにくく、研ぎやすいのが特徴。切れ味を保ちつつ、メンテナンスの負担を軽減してくれます。
現代の日本包丁、特に輸出向けの製品にはこの構造が広く採用されています。
「本焼き」は、一本の高炭素鋼を使用し、刀鍛冶の技術を活かして部分的に焼き入れを行う製法です。クラッドなし、芯材むき出し。全面が高硬度で、まさに職人技の結晶です。
その分、取り扱いは非常にシビア。水気や酸に弱く、錆やすい。研ぎも難しく、ちょっとしたミスで刃こぼれすることもあります。
三枚打ちでは芯材が露出しているのは刃先のみ。そのため、サビやチップなどのダメージは刃先に限定され、研ぎで容易に修復可能です。
しかし本焼きでは、表面全体が反応性の高い鋼材。食材の酸、湿気、水滴などで簡単に変色や腐食が発生し、刃の性能だけでなく見た目にも影響を与えます。
手軽さと実用性を求めるなら、三枚打ちがおすすめ。手間を惜しまず、最高の切れ味と美しさを追求するなら、本焼きという選択肢もあります。
ただし覚えておいてください：芯材の露出が多いほど、それに応じたケアが必要になります。