 By the 1st century AD they had developed puddling for the production of mild steel, crucible steel for the manufacture of things like swords and weapons, and a chemical process of rapidly decarburizing liquid pig-iron to make wrought iron, using the oxidation properties of saltpeter (called the Heaton process, it was independently discovered by John Heaton in the 1860s).China remained the world's largest producer of iron until the 11th century, manufacturing large quantities of relatively affordable steel and iron.Donald B Wagner, an expert in ancient Chinese metallurgy, notes that attempts to trace the history of ironsand in China end with inconclusive results.