Iron metallurgy in Africa
African iron metallurgy encompasses a study of iron production across the continent and an understanding of how it influenced aspects of African archaeology. Extraordinary diversity has originated from iron production creating advanced farming techniques through tools, deadly warfare and valuable items for trade. These developments subsequently influenced social, cultural and political aspects of African life.
Archaeological evidence for iron production has often been based on iron artifacts found in the field. Artefacts are often in poor condition from corrosion and can be unidentifiable. Basing a context of origins to the specimens is unreliable as it is possible that the artifact may have been made somewhere completely different from where it was discovered (possibly even imported!). Solid evidence for iron production includes; the used bowl (foundation) of furnaces, tuyères and slag (from the furnace or forging process). The bloom itself and bellows are rarely found. Evidence of mining and beneficiation of iron ore can also be used as evidence; however it is possible that after beneficiation the ore travelled far to the next stage of production. Evidence for mining is often lost due to more recent mining of iron ore outcrops. Dating can be done through slag analysis and radiocarbon dating of the charcoal used to fuel the furnace. Both of these pieces of evidence are useful as they will always be produced in all smelting even if the technique varies. Metallography and petrographic analysis are also performed on specimens of slag and charcoal to help understand the conditions created within the furnace. Archaeologists have made reconstructions of the technology used for iron smelting as an important process in understanding how the ancient technology worked and to inspire confidence that their perception of the techniques used are correct.
Iron ore is readily available over Africa. Often a diagnostic red colour, it would have made it easy to make surface finds. Common ores used were likely to be hematite, magnetite and limonite (Childs et al. 2005 pg 282). The production process included mining, beneficiation, travel, smithing and forging. The mining and preparation of ores was carried out by men, women and children. It is likely that beneficiation occurred relatively near the site so the iron ore was then ready for transportation to the smelting site or alternatively ready to be traded. The original iron production technique in Africa is thought to have been the 'bloomery process'. Bowl, shaft and natural draft furnaces have been recovered. Iron ore would be put into a furnace along with charcoal at temperatures ranging 1,100–1,200 °C. For this process it would have been necessary for the smelters to use tuyères to blow oxygen into the furnace creating the high temperatures necessary. As the iron separated from the waste slag the raw iron product is called the bloom. The bloom is then removed, reheated and forged by a smith into shapes for use. Evidence from the shape of slag found at smelting sites suggested the furnaces were tapped.
Iron was not the only metal to be used in Africa; copper and brass were widely utilised too. However the steady spread of iron meant it must have had more favourable properties for many different uses. Its durability over copper meant that it was used to make many tools from farming pieces to weaponry. Iron was used for personal adornment in jewelry, impressive pieces of artwork and even instruments. It was used for coins and currencies of varying forms. For example kisi pennies; a traditional form of iron currency used for trading in West Africa. They are twisted iron rods ranging from <30 cm to >2m in length. Suggestions for their uses vary from marital transactions, or simply that they were a convenient shape for transportation, melting down and reshaping into a desired object. There are many different forms of iron currency, often regionally differing in shape and value. Iron did not replace other materials, such as stone and wooden tools, but the quantity of production and variety of uses met were significantly high by comparison.
Social and cultural significance
It is important to recognize that while iron production had great influence over Africa both culturally in trade and expansion (Martinelli, 1993, 1996, 2004), as well as socially in beliefs and rituals, there is great regional variation. Much of the evidence for cultural significance comes from the practises still carried out today by different African cultures. Ethnographical information has been very useful in reconstructing the events surrounding iron production in the past, however the reconstructions could have become distorted through time and influence by anthropologist's studies.
The Iron Age of Africa was based around the agricultural revolution, driven by the use of iron tools. Tools for cultivation and farming made production far more efficient and possible on much larger scales. Fishing hooks, arrow heads and spears aided hunting. Iron weapons also influenced warfare. These items, in addition to the production of other iron goods helped stimulate economic activity, the rise of chiefdoms and even states. The control of iron production was often by ironworkers themselves, or a "central power" in larger societies such as kingdoms or states (Barros 2000, p. 154). The demand for trade is believed to have resulted in some societies working only as smelters or smiths, specialising in just one of the many skills necessary to the production process. It is possible that this also led to tradesmen specialising in transporting and trading iron (Barros 2000, pg152). However not every region benefited from industrialising iron production, some suffered environmentally from problems that arose due to the massive deforestation required to provide the charcoal for fuelling furnaces (for example the ecological crisis of the Mema Region (Holl 2000, pg48)).
Iron smelters and smiths received different social status depending on their culture. Some were lower in society due to the aspect of manual labour and associations with witchcraft, for example in the Maasai and Tuareg (Childs et al. 2005 pg 288). In other cultures the skills are often passed down through family and would receive great social status (sometimes even considered as witchdoctors) within their community. Their powerful knowledge allowed them to produce materials on which the whole community relied. In some communities they were believed to have such strong supernatural powers that they were regarded as highly as the king or chief. For example an excavation at the royal tomb of King Rugira (Great Lakes, Eastern Africa) found two iron anvils placed at his head (Childs et al. 2005, p. 288 in Herbert 1993:ch.6), suggesting their importance and powerful significance. In some cultures mythical stories have been built around the premise of the iron smelter emphasising their god like significance.
The smelting process was often carried out away from the rest of the community. Ironworkers became experts in rituals to encourage good production and to ward off bad spirits, including song and prayers, plus the giving of medicines and even sacrifices. The latter are usually put in the furnace itself or buried under the base of the furnace. Examples of these date back as far as the early Iron Age in Tanzania and Rwanda (Schmidt 1997 in Childs et al., 2005 p. 293).
Some cultures associated sexual symbolism with iron production. Smelting is integrated with the fertility of their society, as with natural reproduction the production of the bloom is compared to the conception and birth. There are many strict taboos surrounding the process. The smelting process is carried out entirely by men and often away from the village. For women to touch any of the materials or be present could jeopardise the success of the production. With the men away from the fertile women it reduces temptation which otherwise could depreciate the productivity of the smelt. The furnaces are also often extravagantly adorned to resemble a woman, the mother of the bloom.
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