San Mai is a Japanese term that literally translates to ‘three parts’. It is a technique used to layer three pieces of steel. Typically in san mai, there will be a high carbon cutting core with a layer of mild steel to either side of the core. There are many different combinations possible with ni and go mai (2 and 5 layers) also being common. They are all considered ‘laminated steel’.
We typically use a high carbon core clad with stainless steel. This gives the best of both worlds. The high carbon core is the only part of the knife that is involved in cutting, so all of the benefits of high carbon steel are present where it counts. The jacket of the knife is stainless steel so will not rust in normal use.
Some of the drawbacks of san mai are that the knife is heat-treated for the core steel, meaning that for stainless-clad san mai, the stainless steel remains soft. This results in a knife that can bend if not used properly and will be less resistant to scratches than a hardened stainless steel. The counter to this is that as it is soft, it is easy to polish and easy to straighten. Whilst rare, a dropped knife that lands on its tip can snap off. The danger of snapping a soft-clad steel is reduced.
On the left is a diagram depicting a san mai knife, where the grey section indicates the outer cladding steel, whilst the black section indicates the core steel.
The example on the right shows a monosteel knife, where the entire blade is made from one, contiguous section of steel.
Due to the core of the knife being high carbon, it will patina or darken over time, leading to dramatic contrast between the steels as seen in the images below. These knives have been etched to darken the core layer.
