Iron (Fe 26). Mined iron ore must be melted at 500℃ or higher to extract the metal, which in alloy form creates steel. The Japanese only started smelting iron to form weapons, armor, and tools sometime in the third to fifth century CE, though before then some iron items were imported from the Korean peninsula. The swords, spears, armor plates, and penknives in the Shōsō-in are made from forged iron, a process that involves repeated heating, folding, hammering, shaping and cooling. The folding leaves marks along the blade, while the cooling creates temper lines.