Shen Kuo's written work of 1088 contains, among other early descriptions of inventions, a method of repeated forging of cast iron under a cold blast similar to the modern Bessemer process.
Chinese metallurgy was widely practiced during the Middle Ages; during the 11th century, the growth of the iron industry caused vast deforestation due to the use of charcoal in the smelting process. To remedy the problem of deforestation, the Song Chinese discovered how to produce coke from bituminous coal as a substitute for charcoal. Although hydraulic-powered bellows for heating the blast furnace had been written about since Du Shi's (d. 38) invention of them in the 1st century CE, the first known illustration of a bellows in operation is found in a book written in 1313 by Wang Zhen (fl. 1290–1333).