Usage & Care: Q4-What Determines the Lifespan of a Knife?

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A Knife’s True Lifespan Lies in Its Construction

The lifespan of a knife is not measured in years, but in how long it can continue to hold an edge. Once the steel is worn away and sharpening is no longer possible, the life of the knife comes to an end. And because not all knives are built the same way, their longevity can differ greatly.

In Japanese knife-making, there are two main construction styles that shape a knife’s durability and sharpening life. Zenkou, also known as all steel or honyaki, is forged entirely from steel and can be sharpened again and again as long as steel remains. In the case of honyaki, however, only the hardened section of the blade can be sharpened indefinitely, while the softer tempered portion cannot be reduced beyond a certain point. Kasumi construction, on the other hand, combines hard steel with layers of soft iron or stainless. Within kasumi, there are important differences: in three-layer kasumi, the steel core runs through the full height of the blade, allowing the knife to be sharpened for many years. In inserted steel kasumi, the core only extends partway down the blade, and once you sharpen past that layer, the edge disappears completely and the knife’s function is lost.

It is often said that a good knife will last forever if you keep sharpening it. In truth, the construction of the blade sets its limits. Many knives sold overseas are of the inserted steel kasumi type, which means they will one day reach a sudden end. The real question to ask is not simply how sharp a knife is today, but how much steel is inside the blade. By understanding this, you can choose a knife that will not only perform beautifully now, but also continue to serve you faithfully for many years to come.