A blast furnace is used to convert raw iron ore into pig iron, which can be further strengthened into cast iron be being remelted in cupola furnaces. The oldest discovered blast furnaces date to the 3rd century BCE and the majority date to after Emperor Han Wudi's reign from 141 - 87 BCE. At that time, a government monopoly was established over the iron industry in 117 BCE. Iron ore smelted in blast furnaces during the Han was rarely placed into permanent molds, and was instead remelted in cupola furnaces to create cast iron. By using a cold blast that traveled through tuyere pipe from the bottom and over the top to where the charcoal and pig iron was placed, the blast became extremely hot once it reached the bottom of the furnace. Although lacking the bloomery, the Han Chinese were able to make wrought iron when they injected excess oxygen into the cupola furnace, causing decarburization. Later the Han Chinese were capable of converting cast iron and pig iron into wrought iron and steel by using the finery forge and the puddling process, the earliest specimens dating back to the 2nd century BCE in Henan province.