text: All indigenous African iron smelting processes are variants of the bloomery process. A much wider range of bloomery smelting processes has been recorded on the African continent than elsewhere in the Old World, probably because bloomeries remained in use into the 20th century in many parts of sub-Saharan Africa, whereas in Europe and most parts of Asia they were replaced by the blast furnace before most varieties of bloomeries could be recorded. W.W. Cline's compilation of eye-witness records of bloomery iron smelting over the past 250 years in Africa is invaluable, and has been supplemented by more recent ethnoarchaeological and archaeological studies. Furnaces used in the 19th and 20th centuries ranges from small bowl furnaces, dug down from the ground surface and powered by bellows, through bellows-powered shaft furnaces up to 1.5 m tall, to 6.5m natural-draft furnaces (i.e. furnaces designed to operate without bellows at all).
  Over much of tropical Africa the ore used was laterite, which is widely available on the old continental cratons in West, Central and Southern Africa. Magnetite sand, concentrated in streams by flowing water, was often used in more mountainous areas, after beneficiation to raise the concentration of iron. Precolonial iron workers in present South Africa even smelted iron-titanium ores that modern blast furnaces are not designed to use. Bloomery furnaces were less productive than blast furnaces, but were far more versatile.
  The fuel used was invariably charcoal, and the products were the bloom (a solid mass of iron) and slag (a liquid waste product). African ironworkers regularly produced inhomogeneous steel blooms, especially in the large natural-draft furnaces. The blooms invariably contained some entrapped slag, and after removal from the furnace had to be reheated and hammered to expel as much of the slag as possible. Semi-finished bars of iron or steel were widely traded in some parts of West Africa, as for example at Sukur on the Nigeria-Cameroon border, which in the nineteenth century exported thousands of bars per year north to the Lake Chad Basin. Although many African ironworkers produced steel blooms, there is little evidence in sub-Saharan as yet for hardening of steel by quenching and tempering or for the manufacture of composite tools combining a hard steel cutting edge with a soft but tough iron body. Relatively little metallography of ancient African iron tools has yet been done, so this conclusion may perhaps be modified by future work.
  Unlike bloomery iron-workers in Europe, India or China, African metalworkers did not make use of water power to blow bellows in furnaces too large to be blown by hand-powered bellows. This is partly because sub-Saharan Africa has much less potential for water power than these other regions, but also because there were no engineering techniques developed for converting rotary motion to linear motion. African ironworkers did however invent a way to increase the size of their furnaces, and thus the amount of metal produced per charge, without using bellows. This was the natural-draft furnace, which is designed to reach the temperatures necessary to form and drain slag by using a chimney effect – hot air leaving the topic of the furnace draws in more air through openings at the base. (Natural-draft furnaces should not be confused with wind-powered furnaces, which were invariably small). The natural-draft furnace was the one African innovation in ferrous metallurgy that spread widely. Natural draft furnaces were particularly characteristic of African savanna woodlands, and were used in two belts – across the Sahelian woodlands from Senegal in the west to Sudan in the east, and in the Brachystegia-Julbenardia (miombo) woodlands from southern Tanzania south to northern Zimbabwe. The oldest natural-draft furnaces yet found are in Burkina Faso and date to the seventh/eight centuries  The large masses of slag (10,000 to 60,000 tons) noted in some locations in Togo, Burkina Faso and Mali reflect the great expansion of iron production in West Africa after 1000 CE that is associated with the spread of natural-draft furnace technology. But not all large scale iron production in Africa was associated with natural draft furnaces – those of Meroe (Sudan, first to fifth centuries CE) were produced by slag-tapping bellows-driven furnaces, and the large 18th-19th century iron industry of the Cameroon grasslands by non-tapping bellows-driven furnaces. All of the large-scale iron smelting recorded so far are in the Sahelian and Sudanic zones that stretch from Senegal in the west to Sudan in the east; there were no iron-smelting concentrations like these in central or southern Africa.
  There is also evidence that carbon steel was made in Western Tanzania by the ancestors of the Haya people as early as 2,300-2,000 years ago by a complex process of "pre-heating" allowing temperatures inside a furnace to reach up to 1800°C.
  These techniques are now extinct in all regions of sub-Saharan Africa, except, in the case of some of techniques, for some very remote regions of Ethiopia. In most regions of Africa they fell out of use before 1950. The main reason for this was the increasing availability of iron imported from Europe. Blacksmiths still work in rural areas of Africa to make and repair agricultural tools, but the iron that they use is imported, or recycled from old motor vehicles.