Metallurgy-the science of working with metals such as iron in order to give them certain desired properties-has a long history. The first known objects made from metals date to the ninth millennium B.C.E. Usable iron is usually obtained from iron ore(raw iron)by smelting, a process by which iron is separated(reduced)from its ore by heating. Iron-ore smelting requires very high temperatures and good control of the temperature and reduction conditions. Achieving these was beyond the capabilities of the early metallurgists. Thus, the development of the earliest metallurgy concerned only other metals-gold, silver, copper, lead, and tin-around which a range of sophisticated technologies developed, practiced by experts and often managed by elites. The rarity of tin required for making bronze, played a key part in determining the pattern of trade routes, and the consequent expense restricted bronze use to important members of society.

In about 1200 BCE, however, iron smelting began in western Asia. Iron ore needed to be reduced in a furnace at a high enough temperature to ensure that the slag(the material from which the iron has been separated) melted and ran off, leaving the iron “ bloom”. A blown-air supply, provided by a device called a bellows, enabled the fuel to burn. The resulting bloom was a mass of metallic iron still containing impurities from the fuel, which had to be driven out by forging(heating and hammering), leaving wrought iron, a soft inferior metal that could not be hardened by heating. Carburization, however, transformed wrought iron into useful low-carbon steel by incorporating 0.5 to 1.5 percent carbon, generally by using charcoal as the smelting fuel Low-carbon steel was harder and stronger than bronze, and could take and keep an edge better; and its hardness could be varied by heating and cooling it. Skilled and nuanced ironworking developed thereafter-expert smiths in western Europe, for example, produced swords with razor-sharp edges, hard, but easily broken, on softer, more elastic blades.

The technology of smelting and working blooms was relatively simple, requiring little specialist equipment: an easily constructed bowl furnace into which the iron and charcoal fuel are placed, and bellows to enable the temperature to be raised, as well as tongs, hammer, and anvil to turn the bloom into usable wrought iron and work it into objects. Iron has the convenient property that pieces can be joined strongly by hammering them together while heated(welding). The technology was therefore accessible to ordinary people with the necessary skills rather than being confined to specialists, stimulating the emergence of small-scale entrepreneurs, such as the itinerant smiths of Iron Age Europe. In addition, iron ores are abundant and found everywhere. While some regions with substantial or high-quality ore sources became wealthy by trading in iron, most regions were able to obtain iron relatively locally and cheaply, altering the patterns of trade. Bronze supplies were now devoted to the production of luxury goods, such as fine jewelry, elite tableware, and ceremonial armor Iron objects became common with metal tools, weapons, and armor now within the reach of everyone. This had a considerable impact on the efficiency of many aspects of everyday life, such as agriculture, industry, and construction, as well as warfare. Iron had advantages over bronze because it was harder, more durable, easy to repair, and easy to shape. It is thought that the advent of ironworking also had a democratizing effect, affecting social organization.

In China the path of development was different. While wrought iron was made there, the Chinese developed furnaces capable of achieving the temperature required to produce cast iron, which was higher in carbon content and harder, using a blast furnace to produce a powerful forced draft, something not achieved elsewhere until many centuries later. This meant that they were able to mass produce iron objects by casting (pouring and allowing to solidify in a mold). Iron was produced on a large scale by elites in large iron foundries. The development of ironworking, therefore, did not have the same social impact as elsewhere, although it enabled ordinary individuals to acquire metal tools.