The stage in human cultural and technological development called the Iron Age is characterized by the smelting of iron and its widespread use in tools. Smelting is a process through which metalworkers extract a metal from an ore (metal-containing rock). The Iron Age followed the very long Stone Age, in which tools were made mainly from stone, and the shorter Bronze Age, in which they were made of bronze. Iron is a better metal than bronze for making tools and weapons because it is harder and tougher. Even more important, iron ore is much more widely distributed and readily available in surface deposits around the world than the ores of copper and tin, which are both needed to make bronze. While metal implements were fairly rare and expensive during the Bronze Age, they ultimately became relatively commonplace during the Iron Age. Eventually, even the masses of peasants had access to iron tools and weapons.
Different cultures began smelting iron at different times. The Iron Age is usually considered to have begun in the Middle East and southeastern Europe in about 1200 to 1000 bc, when iron tools came into wide use. Iron had been known and used in limited ways, however, in earlier times. Iron Age industries were later established in Egypt and other parts of Africa, in northern and western Europe, and in India, China, and other parts of Asia. European explorers and colonizers later introduced Iron Age products into areas with Stone Age cultures, including in the Americas and Oceania.
The smelting of iron requires heating the metal to higher temperatures than does the smelting of copper. Metalworkers in the Iron Age built improved furnaces to accomplish this. Ancient iron smelting involved heating the iron ore along with charcoal, which served as both a fuel and a reducing agent. This produced a spongy lump of iron and slag (waste) that was hammered to remove nearly all the slag. The surface of the iron was then heated again within a bed of glowing charcoal. This enabled the iron to absorb carbon from the charcoal and develop a coat of steel. The steel surface was further hardened by heating it and then cooling it rapidly. The iron was shaped into tools by heating and hammering. The technology did not yet exist to heat the iron enough to fully melt it and cast it in molds like bronze. For this reason, early iron tools had a less refined appearance than cast bronze ones.
