English: A katana of the kobuse type, made in the traditional Japanese style. The hardened edge is separated from the softer back by a bright, wavy line, called the nioi. The edge of this bright line, called the hamon, marks the boundary between the martensitic portion (the yakiba) from pearlitic center area (the hira). The wavy shape of the hamon is from the manner in which the insulating clay was appllied before quenching. The inset shows a close-up of the nioi, which is made up of niye. The niye are single, bright grains of martensite surrounded by pearlite, which are seen as the speckled zone between the bright yakiba and the darker hira. The wood-grain appearance comes from alternating layers of steel that have different hardenability.