Grand Seiko Heritage Shingane Watch, 40mm Green Dial, SBGA491

To craft a katana, iron sand is first drawn from the Earth and heated in a clay furnace. The sand is transformed into tamahagne, a pure form of Japanese steel. Derived from tamahagane are two variations of steel, one of which is shingane, used for the strong inner core of the blade. The resilience and strength of shingane are represented in the dark green dial of the US Exclusive SBGA491.