The San Mai technique, also known as 'three-layers' or 'metal sandwich', is a blade creation technique of Japanese origin, to create a blade of three different types of steel.
In the San Mai technique, three layers of metal are used and forge-welded together. The two outer layers are one type of metal (usually softer), with a different type (harder) of metal on the inside. The outer layers are made using more shock-absorbing metal to increase resistance to impact, whereas the inner layer of metal is made from a harder metal to give the blade strength.
This gives the blade a very strong toughness while also maintaining flexibility and avoiding brittleness.
Having three types of steel in the blade also makes it possible to add unique styling and flair to the blade, compared to more traditional mono steel (where only one type of steel is used).
When is San Mai Used?
San Mai, being a 'technique' rather than a 'type' of blade, is widely used. San Mai has been used to create knives, kitchen knives, hunting knives, swords and more.
Why and where was the technique invented?
The san mai or three-layered technique originates in Japan. While the technique is still widely used today due to the benefit of a hard yet still flexible blade, it was originally created for a practical purpose. Back around the time it was invented, there were less resources available than there are today. As such, hardenable steel - like the type used on the inside of the 'sandwich', to give the blade strength - was not widely available. By spreading the 'harder steel' using the san mai technique, smiths were able to make their scant quantities of harder steel go further, while still maintaining great quality blades.
San Mai Today
The technique is still commonly seen today and has even been explored in TV shows such as "Forged In Fire":
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