By the time of the Kamakura period (1185–1333 AD), Japan was under the rule of a military class and repelling Mongol invasions.
This technology included folding, inserting alloys, and differential hardening of the edge, which historically has been the most common technique around the world.
While the Japanese would be more influenced by the Chinese dāo (single-edged swords of various forms), the early Japanese swords known as ken are often based on the jian.
This is still in debate as metallurgist John Verhoeven at Iowa State University believes the nanowires to occur in most steels.
The other is a composite structure made by welding together iron and steel to give a visible pattern on the surface, called pattern welded steel.
During the Hallstatt period, they made swords both in bronze as well as iron with rounded tips.
Toward the end of the Hallstatt period, around 600-500BC, these swords were replaced with short daggers.
The term Damascus steel can refer to two different types of artefacts.
One is the true Damascus steel, or Wootz steel, which is a high carbon alloy with tremendous edge retention possibly due to its composition of carbon nanotubes and carbide nanowires, with a wavy surface texture originating from the crystalline structure of alloy metals such as tungsten and vanadium - elements that occur naturally in iron ore from southern India - to the surface during the manufacturing process.
The central plate protrudes slightly from its surrounding pieces, allowing for a sharp edge, while the softer spine protects the brittle core.