Artistry of the Katana—U.S. Exclusive Models influenced by the materials and craft of the blade. The Japanese sword, known as the katana, is a world-renowned masterpiece in steel. Crafted through a distinctive and sophisticated process, the katana has created fascination and allure the world over. Derived from nature and brought together through expert craftsmanship, the katana is made from earth, fire, water, and air. Iron sand is drawn from the earth and then heated in a furnace known as a tatara. The melted sand forms the Japanese steel, known as tamagahane. From this Japanese steel, two variations can be found. The first is the high-carbon steel used for the outer sharp edge, or kawagane, and the second is the strong inner core of the blade, or shingane. Grand Seiko honors the katana and shingane with the U.S.-exclusive SBGA491.