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.
William Kelly (inventor)
Before the technique of injecting air into molten iron was re-discovered by Kelly and by Bessemer, iron was available as cast iron, a strong but brittle metal made in a blast furnace by treating iron ore with coke derived from coal, and wrought iron, a more malleable and flexible metal made by heating iron ore in a low oxygen environment in a bloomery heated by charcoal and producing "blooms", which were 100 to 200 pound lumps of very low carbon iron mixed with slag. The blooms then had to be worked repeatedly by hammering with a helve hammer or later a steam hammer and folding it to work out the slag. This could in turn be converted to steel by heating it for prolonged periods sealed in stone boxes with charcoal, to add back carbon. The resulting steel could then be formed into larger shapes by heating it to welding temperature and hammering it together into a mass. Other laborious and expensive methods made small amounts of steel from special ores.