On the craft
Understanding Sanmai - Stainless Clad
Sanmai is a common construction for double bevel knives where two pieces of softer cladding steel are forgewelded to each side of a harder core steel. The harder but more brittle core steel will form the hard cutting edge after heat treating, and the softer cladding will support the core to increase the overall strength of the blade.
Besides the strength, some carbon knife can benefit greatly from the sanmai construction. With a layer of stainless material cladded on both side, the carbon knife made with Hitachi Blue or White steel that was prone to rust and discoloring will have most of its surface covered by the cladding. This can greatly reduce the amount of maintenance required, as the carbon core is only exposed near the very edge of the bevel.
Due to this weldforging cladding, Sanmai as well as Nimai, will have a distinctive cladding line near the cutting edge, where two types of material meet. This add another layer of aesthetic to the blade compare to the monosteel construction, and for the stainless Sanmai, this also marks where the carbon or semi-stainless core steel is exposed, and care and maintenance is needs.
The cladding is produced separately from the core before they are foregewelded on, this allows makers to clad their blade with different materials like damascus to introduce different esthetic features to the knife without affecting the cutting performance.
Due to the hardness difference between the core and cladding, they will react differently when certain finish is applied. After the bevel of a sanmai knife undergone a kasumi finish(霞研ぎ), the harder core will present a higher polish whereas the softer cladding will present a dreamy, cloud-like satin finish. The curvy boundary between two finishes lead to a beautiful bevel that looks like the surface of a lake with fog floating above. Even without the kasumi finish, the usually noticeable cladding line can add visual interests to the knife with sanmai construction.
