What is san mai?

San mai is a traditional Japanese technique used in sword making, primarily for crafting katana blades. The process involves sandwiching a core of high carbon steel (hagane) between two outer layers of lower carbon steel (jigane). This creates a blade with a hard, sharp edge while maintaining flexibility and durability.

The layers are forge-welded together, resulting in a visually distinctive pattern known as the "hada" or grain pattern. The outer layers are often made of softer, more ductile steel to provide support and absorb shock, while the hard core steel holds a sharp edge.

San mai blades are known for their superior cutting performance, edge retention, and overall strength. They are highly prized by collectors and martial artists for their craftsmanship and quality.

Overall, san mai is a time-honored technique that continues to be used in Japanese sword making to create high-quality, functional blades that are both beautiful and durable.