Iron ore
In cast iron sulfur promotes the formation of white iron. As little as 0.5% can counteract the effects of slow cooling and a high silicon content . White cast iron is more brittle, but also harder. It is generally avoided, because it is difficult to work, except in China where high sulfur cast iron, some as high as 0.57%, made with coal and coke, was used to make bells and chimes . According to , good foundry iron should have less than 0.15% sulfur. In the rest of the world a high sulfur cast iron can be used for making castings, but will make poor wrought iron.
Science and technology of the Han dynasty
A blast furnace converts raw iron ore into pig iron, which can be remelted in a cupola furnace to produce cast iron. The earliest specimens of cast iron found in China date to the 5th century BCE during the late Spring and Autumn period, yet the oldest discovered blast furnaces date to the 3rd century BCE and the majority date to the period after Emperor Wu of Han (r. 141–87 BCE) established a government monopoly over the iron industry in 117 BCE (most of the discovered iron works sites built before this date were merely foundries which recast iron that had been smelted elsewhere). Iron ore smelted in blast furnaces during the Han was rarely if ever cast directly into permanent molds; instead, the pig iron scraps were remelted in the cupola furnace to make cast iron. Cupola furnaces utilized a cold blast traveling through tuyere pipes from the bottom and over the top where the charge of charcoal and pig iron was introduced. The air traveling through the tuyere pipes thus became a hot blast once it reached the bottom of the furnace.