Preindustrial Mining and Metallurgy in Africa
- Foreman BandamaForeman BandamaSol Plaatje University
Africa hosts some of the oldest mines (for exploiting ochre used in personal adornment) in the world, but the ones that relate to the transformation of rocks to metal occur much later when compared to those found in Eurasia. Throughout the world, the processes of identifying and winning ores from parent rock in order to transform them into metals and, ultimately, into usable objects is indeed considered to be a novelty. African ethno-archaeological research suggests that the realization that certain rocks contained sufficient quantities of metal for heat-mediated reduction into metals, as well as the appreciation of the different properties of targeted metals, have never been difficult issues to the local Africans but archaeometallurgists are still rationalizing how this novelty began without an apprenticeship phase, especially south of the Egyptian pyramids. Indigenous sub-Saharan Africa metallurgy is laden with symbolism, ritual, and taboos. This particular aspect made the whole craft to be derided by Western science as magical and therefore unworthy of proper scientific study. This prejudiced thinking has since been discredited by sound research, but the ripple effects still linger and archaeometallurgical research is still generally underfunded when compared to other elements of anthropological inquiry. Nonetheless, the limited research conducted to date firmly highlight the direction of preindustrial mining and metallurgical research in this region. In a pattern unknown in Eurasia, where copper and bronze preceded iron production in a very gradual process, sub-Saharan Africa metallurgy was ushered in by the simultaneous advent of iron and copper in parts of East, Central, and West Africa before this metallurgy was introduced to the southern subcontinent. Gold, tin, and cuprous alloys (mostly bronze and brass) were then introduced after centuries of ongoing iron and copper metallurgy. As the last block to take up metallurgy, Southern Africa is often uncritically assumed not to have had an innovative aptitude, but the historiography of mining and metallurgy of the whole sub-Saharan Africa constantly evokes prejudiced thinking about African incapacity or the counter discourse. A more careful reading of sub-Saharan metallurgy literature places this craft at par with the equivalent from Eurasia. Considering that the African continent is the cradle of humankind, this is not surprising. Fortunately, as products of a high-temperature process, archaeometallurgical objects and waste by-products retain in their physical and chemical properties partial histories of the transformations they went through, allowing archaeometallurgists glimpses into the technologies of past societies. Guided by concepts such as “materiality” and in agreement with Maussian thinking, Africanist archaeometallurgists consider the so-called magic to be just as important as the technical control because there is no chasm between the technological and anthropological factors of artifacts, and all technologies falls within the broader social paradigm of their construction.
Introduction to Indigenous African Metallurgy
The locus and locale of this study is Africa, the 30,301,596 square kilometers land mass that is spatially superior to the combined size of India, the United States, China, Argentina, and Europe. The unsurmountable task of unpacking the various aspects of preindustrial metallurgy makes the partitioning of Africa into blocks inevitable. While this task is achievable, the north–south division of the African continent should be adequately explained because prejudiced Westerners, such as Hegel (1748, republished 1956, 99) unscrupulously maintained that North Africa is no part of Africa because of connections with Eurasia and that beyond this subcontinent, Africa itself does not exist (no history, no movement, and no development). With an apology to Africanists, the author maintains the north–south divide for nothing more than convenience that is driven by the patterns, purposes, paces, and periods of metallurgy that appear to be distinct between parts of north Africa (Egypt in particular) and sub-Saharan Africa. This work has a strong sub-Saharan Africa bias. In this broad region, metallurgical histories are further divided into West, Central, and East Africa on one block and Southern Africa on the other (Figure 1).
It is also unfortunate that any discourse about precolonial Africa cannot totally escape the modern boundaries drawn at the 1884–1885 Berlin Conference (Figure 1), but the contextual understanding of these places does not necessarily follow these national borders.
The first African participant of metallurgy is Egypt (5000–3000 bce). This took place in the Eurasian Copper Age, and for Egyptians and Eurasians, their initial motivation lay in the appreciation of the colors (luster) of native copper and its ores as grave goods for adorning the dead. They later discovered that heat could transform the colors of these ores, and in this way, melting followed. Accordingly, simple melting preceded formal smelting and, just like in Eurasia, Egyptian metallurgy was adopted very gradually, from the Copper Age to the Bronze Age (3000–1500 bce) before mastery of the technologically complex iron (Iron Age c. 800 bce onward). However, the advance of iron technology (with iron physically superior to bronze in the utilitarian sphere) in Egypt was halted by millennia-old social prestige issues and chiefly networks that preferred bronze until after the invasion by the Assyrians. Egypt is not alone in this regard, as southern Scandinavians also rejected iron metallurgy for several hundred years because of the preference toward bronze, which was held in high regard by nobility and was embedded in social prestige (Kristiansen 2005, 154). Other parts of North Africa appear to have received metallurgy from the Phoenicians around 800 bce, but there is no evidence of a southward Phoenician penetration beyond these regions, nor do the patterns southward show resemblance to the northern metallurgical picture.
In sharp contrast to Egypt, North Africa, and Eurasia, metallurgy in West, Central, and East Africa kick-started with the still contested simultaneous working of iron and copper before 800 bce. With Eurasia having taken millennia to master iron metallurgy, the almost inexplicable simultaneous introduction of iron and copper, presumably without external help, was bound to be challenged. The debate about these dates is discussed in the following section (see “On the Origins Debate”), but it suffices to say that metallurgy in West, Central, and East Africa took a different pattern from, served a different purpose, and spread much faster at a later date than that of Eurasia. Southern Africa is the last African block to receive metallurgy, but its picture mimics that of its immediate neighbors (West, Central, and East Africa) from whence came the technology and the people (ancestral Bantu) early in the 1st millennium ce. This picture extends to the inception of gold, tin, and alloyed copper, which lagged behind iron and copper metallurgy in the whole of sub-Saharan Africa until the intensification of long-distance trade via the Indian Ocean rim (East and Southern Africa) and trans-Saharan route (West Africa). The pattern contrasts with the initial working of gold, copper, and later bronze before the inception of iron technology in Egypt and Nubia (Figure 2).
On the Origins Debate
The search for the origins of innovations (not just metallurgical innovations) is never straightforward. Figure 2 shows the limited range of metals worked in preindustrial Africa involving at least four metals (gold, tin, iron, and copper and its alloys). For sub-Saharan Africa, the histories of these metals contrast with the earlier established chronology for Eurasia in which copper was worked first, followed by bronze, and then iron in a very gradual process lasting several millennia. In sub-Saharan Africa (West, Central, and East Africa in particular), the simultaneous appearance of iron and copper appears to have ignited a long-lasting debate on whether this technology is autochthonous, even though the initial exchange never involved any sound archaeological data (Lhote 1952; Mauny 1952; Alpern 2005; Zangato and Holl 2010; Killick 2016). One of the two opposing camps has remained theory heavy (scenario and hypothesis driven), while the other has called for the supremacy of actual archaeological data.
The single origin and external origin hypothesis holds that metallurgy was discovered once in Eurasia before it was subsequently introduced to Africa. For the proponents of this hypothesis, the complexity of iron (related to temperature regimes that are higher than those for copper and its alloys) makes it unimaginable that the Africans would have figured out how to work it without prior apprenticeship phases, as was the case in Eurasia where copper and bronze were worked for millennia before the mastery of ferrous metallurgy (Phillipson 1985, 149). To account for the appearance of metal in sub-Saharan Africa, conduits (Carthage and Meroe) were suggested. Unfortunately, these conduits could not be valid because their iron chronology is synchronous or later than the dates for some sites in the West, Central, and East African interior. As a reaction to the external origin hypothesis, a counter view proposing a local and multiple origin hypothesis was inevitable.
The local and multiple origins hypothesis initially rose as a reaction to the external origins hypothesis and articulated its argument on the basis of the diversity and ubiquity of iron technology in Africa, which was thought to suggest a deep-seated culture of experimentation that made possible the discovery of iron metallurgy without external assistance. In this regard, sub-Saharan Africa would not have been alone because experimentations are thought to have triggered metallurgical discoveries in various other places such as Serbia, Anatolia, India, and the Americas (Radivojevic et al. 2010, 2013; Chirikure 2014). A handful of radiocarbon dates within the range of 2000 and 800 bce have since been accumulated in places such as Mauritania, Nigeria, Niger, Central Africa Republic, Senegal, Togo, Burkina Faso, and the Great Lakes Region (Clist 1989; Grebenart 1988; MacEachern 1996; Deme and McIntosh 2006; de Barros 2006; Pringle 2009; Eze-Uzomaka 2009; Zangato and Holl 2010). A few of these dates have been found to be problematic, and to some researchers, this weakens the status of the rest of the dates, and calls for their corroboration by other methods such as thermoluminescence dating have been echoed (Killick et al. 1988; Killick 2004, 2009). The realization that the majority of these dates fall within the radiocarbon black hole further strengthens the challenge on the status of these radiocarbon dates, but local origin hypothesis proponents still maintain that the several radiocarbon dates outside this black hole are enough to fortify the argument that sub-Saharan Africa discovered metallurgy independently.
A cursory look would suggest relative calm with regard to the origins of metallurgy in Southern Africa because the first metals here were introduced from West and East Africa around 200 ce. Contention exists with regard to the advent of tin and bronze metallurgy in this region. In contrast to the Eurasian case, innovations in tin and bronze in Southern Africa were additions to already vibrant and deeply embedded iron and copper metallurgical traditions. Because iron was already in use, it also meant that, unlike in Europe, the demand for bronze was outside of the mechanical of the alloy hardness, which is higher than either tin or copper (Herbert 1984). Instead, the innovation of tin, and especially bronze, may consequently be sought in its value in the expressive sphere, suggesting a preexisting appreciation of bronze which could not be adequately satisfied by ongoing copper metallurgy (Bandama, Hall, and Chirikure 2015). Some researchers have suggested that the fact that bronze resembles gold could have triggered the innovation in bronze and that the presence of the culturally preferable copper (in bronze) cemented the preference of the alloy over the noble metal (Miller 2003; Killick 2009). The simultaneous discovery of both tin and bronze means that one cannot hypothesize a random discovery of bronze production through an unintentional exploitation of mixed copper–tin ores. In Southern Africa, most tin was alloyed with copper to make bronze, other than ingots and rare instances of earrings, hilts for daggers, and tongs (Thompson 1954; Herbert 1984; Miller 2002; Bandama et al. 2016). Because bronze production was already in full swing in Eurasia by the second millennium ce (Craddock 2001), southeast African coastal traders may have learned about bronze from Eurasians and diffused the idea into the region (Miller 2002; Killick 2009). Yet, unlike gold, which mainly fed into overseas markets, this alloy was never exported out of the subcontinent in significant quantities, leaving regional elite centers as the logical node for the demand for tin and bronze production in Southern Africa (Bandama, Hall, and Chirikure 2015).
The Chaine Operatoire of African Metallurgy
As a signature craft technology, it is not surprising that metal working in Africa has a complicated history and that its production line is far from sequential. Depending on the type of metal, the chain of events (chaine operatoire) for metal objects habitually starts with the search for (prospecting), acquisition of (mining and collecting), and preparation of raw materials (beneficiation of ores and charcoal processing), followed by the building of a reaction infrastructure for smelting (tuyere and furnace construction), smelting (heat-mediated reduction of ores to metal), bloom cleaning, smithing, and forging, before they enter the use, discard and recycle contexts (see Figure 3 for an example of iron production). Other metals are mostly variants of this pattern with the exception of the melting, alloying, and casting stages for nonferrous metallurgy. Discussion of nonferrous production lines is given in subsequent sections.
Prospecting: Seeing and Searching for Metal in Rocks
Throughout the world, metallurgy rarely commenced with a systematic search for ores to use in smelting. Instead, unconscious discoveries led to the realization that certain types of rocks contained sufficient metal for smelting or melting. Once learned, metal workers in Africa subsequently mastered the techniques of identifying and locating metal-containing rocks using rudimentary but effective prospecting methods. The pinpoint accuracy of such methods is underlined by the realization in countries such as Zimbabwe, South Africa, Ghana, and Zambia, to mention a few, that rich ore bodies were exploited before the onset of, and directed modern prospecting (Summers 1969). Rudimentary prospecting methods included a reading of the geology, soil, and vegetation, water tasting downstream, as well as following alluvial deposits upstream. For much of sub-Saharan Africa, prospecting (just like the rest of metallurgical activities) was never a purely technical exercise but one that required the blessing, guidance, and intervention of the spirit world. Accordingly, this practice was often preceded by rituals in order to invoke the good will of ancestors, evade negative spirits, and sanctify oneself for successful hunting and gathering of ores (Buleli 1993; Chirikure 2006, 2015; Haaland 2004). Unfortunately, for a long period of time, Western science could not comprehend how such magical activities aided technical processes; thus, the whole craft was derided as unscientific and therefore not worthy of study. Once the ores were located and identified, the next task was to collect and carry them to the processing area.
Mining: Winning Ores from Rocks
Southern Africa hosts one of the oldest mines in the world, with about 40,000 years of exploitation on the Bomvu Ridge in Swaziland (Dart and Beaumont 1971), but these mines were only for iron-rich specularite use for decorative purposes without actual reduction into metal. The actual collection and use of such minerals go even deeper into antiquity, dating to around 120,000 years ago, when Middle Stone Age people in parts of South Africa processed specularite for making pigments. Specularite (for decoration) and haematite (for smelting) ores have the same chemical composition (Fe2O3) and crystalline structures under the microscope, the only significant difference being the aggregation of minute crystals, which form a single crystal in specularite compared to aggregates in haematite. In hand specimens, haematite ores had a red-brown color and a red streak on the fresh breaks, but unlike specularite, they do not have bright shining sparkles. Together with magnetite and banded ironstone, haematites are the chief ore types in sub-Saharan Africa. Special mention goes to the Chewa people of Malawi who worked low-grade laterites that are not considered economical in blast furnace technology (Killick 1990). Erudite selection of ores was so important because in some instances, the success of a smelt depended on this process. For instance, minimal viscosities in iron slags occur only in a narrow range of temperatures and compositions, which in precolonial times may have been controlled by choosing particular ores over and above varying the proportion of ore to fuel and varying the force of the blast (Rostoker and Bronson 1990).
Throughout sub-Saharan Africa, mining for iron ores was rarely a subsurface process when compared to copper, gold, or even tin mining. Exceptions do occur as noted by the occurrence of subsurface precolonial iron mines near Thabazimbi in South Africa (Woodhouse 1974) and the Mouhoun Bend in Mali (Holl 2014). Simple quarrying or surface collection would have sufficed for most ferrous ores, but when needed, hard rock mining commenced by sinking vertical or inclined shafts using iron gads (chisels) and hammers. A similar approach was employed for hard rock mining of copper, tin, or gold ores, but often these nonferrous mines were deeper (as far as the water table) and developed into underground shafts, according to ore mineralization. Narrow audits and stopes for ventilation and lighting were other innovations erroneously associated with child miners by some researchers (van der Merwe and Scully 1971; Herbert 1984, 45). Other innovations in nonferrous mines included fire-setting to break hard rock and reach desired ores. The complexity and know-how in sub-Saharan hard rock mining for copper, tin, and gold ores was significant enough to cause prejudiced Europeans to deny black African authorship of some of these mines. Black Africans were relegated to mere laborers under coercion from their superior foreigner masters (Semitic or Arab races) (Summers 1969; Hammel et al. 2000). In Southern Africa, gold and copper mining (and occasionally iron mining) is associated with dolly holes (grooves typically made on granitic surfaces for processing metal and ores) (Huffman 1974).
Most precolonial copper mines have been obliterated by modern mining activities, but the pattern for their distribution can still be inferred today. Copper mines are rare in East Africa and they are not widespread in West Africa except in a few places such as Akjoujt (Mauritania) and Agadez (Niger) (Lambert 1983). The richest copper ore deposits in Sub-Saharan Africa that were exploited in preindustrial times include the Lufilian Arc covering the Central African Copper Belt in modern-day Democratic Republic of the Congo (DRC) and Zambia (Bowen and Gunatilaka 1977, 129; Bisson 1976). The Zimbabwe Plateau, parts of eastern Botswana, and northern South Africa also host significant precolonial mines (Summers 1969; Swan 1994; Thondhlana 2012).
To date, unequivocal evidence for preindustrial mining for tin in sub-Saharan Africa appears to be limited to two areas: Rooiberg in northern South Africa and the Jos Plateau in Nigeria. Besides hard rock mining, it is possible to pan for tin ore because cassiterite (the richest tin ore) is a dense ore that can be easily separated from other lighter materials (Tylecote 1962, 63). In Rooiberg, the occurrence of alluvial cassiterite as part of the tin feed at some of the smelting sites has been reported and physiochemical analyses of tin slags from some sites confirm the presence of heavy elements such as zirconium, which were most likely retained together with cassiterite during alluvial panning (Wagner and Gordon 1929, 568; Miller and Hall 2008; Chirikure, Heimann, and Killick 2010; Bandama, Hall and Chirikure 2015). Alluvial panning for tin ore has also been mooted in the Jos Plateau (Hodder 1959). Unfortunately, cassiterite panning leaves very little archaeological traces, and there are other unconfirmed candidates throughout the region such as in Zimbabwe and South Africa.
Panning, one of the oldest mining techniques in Africa, is almost synonymous with precolonial gold working in sub-Saharan Africa, but hard rock mining was also practiced for the noble metal. Other fascinating exceptions include the East African Kikuyu women and the West African Mafa people who panned magnetite sands for iron smelting (Cline 1937). The same principle of density separation worked in gold panning, with the noble metal being easier to spot in the gangue due to its signature glittering shine. Minor variations exist, but generally the technique involved scooping and shaking of mineral-rich sand into a receptacle. Alluvial gold panning was practiced in the Nubian Desert, in the auriferous zones of Bambuk between Senegal and Falene Rivers, Bure around Upper Niger, the Akan region of Ghana, the Anyi and Baule regions of Ivory Coast, the greenstone belt of the Zimbabwean plateau, and parts of Zambia and northern South Africa. Of these cases, the men who dove into the river bed of the Ankobra in southern Ghana caught the attention of some early writers and there is an image from a 1668 book (Description of Africa, by Olfert Dapper) published in Amsterdam that depicts this practice (Habashi 2009).
Melting and Smelting: Winning the Metals from Ores
Meteoric metal and gold (which exist in native form) are the only examples that did not require smelting in refractory installations. In ancient Egypt, native copper would be used for adorning the dead, but later, copper was melted for other decorative uses. As for gold, throughout sub-Saharan Africa, the dust or nuggets of this noble metal were melted in crucibles to consolidate them into ingots or, rarely, into cast, hammered, or drawn objects.
Iron, tin, and copper ores were reductively smelted in various forms of forced or natural draught furnace installations. Unlike areas to the north, the highly reducing tall shaft (natural draught) furnaces were limited to sub-Saharan Africa (Chirikure and Bandama 2014). These furnaces could also produce significant quantities of iron per smelt. Strictly speaking, natural draught furnaces were a preserve for iron smelting, with copper and tin smelting being limited to forced draft furnaces. There is evidence, however, from Kansanshi in the 12th century (Chirikure 2018), for unrepeated experimentation with reducing copper in natural draught furnaces. Whichever furnace installation was employed, all smelting was preceded by charcoal preparation, beneficiation of ore, and furnace preparation. Even for highly ritualized sub-Saharan Africa iron smelting, it is not surprising that mining, charcoal preparation, and transportation of ores and fuel were sometimes relaxed to ensure maximum utilization of labor through the mobilization of women and children. The Bassar (Togo), Babungo (Cameroon), and Njanja (Zimbabwe) are some examples of this practice. Beneficiation was often carried out with hammerstones (or iron hammers) and anvils, and some of the gangue materials could be physically removed during this process.
The African bloomery smelting process is relatively better known but varied and replete with innovations and experimentations. This solid-state reduction technique involved lowering the melting point of gangue using a self-fluxing recipe, and thus melting the impurities at temperatures in excess of 1200 degrees Celsius, leaving a metal-rich slagged bloom. The flux often came from the fuel ash, the melting furnace wall, or tuyere, but in northern South Africa, there have been reports of occasional additions of sand (Prendergast 1974; Bandama, Chirikure, and Hall 2013). After smelting, the occluded slag and entrapped charcoal fragments still required cleaning and consolidation under a forge.
Reductive copper smelting happened either in clay furnaces or in crucibles under reducing conditions. Reduction was necessary because most African copper ores occurred as oxides or carbonates. Just as with iron smelting, the incomplete combustion of charcoal created carbon monoxide, necessary for reducing ores to usable metal at temperatures above 1000 degrees Celsius. However, unlike iron smelting, some copper smelts would have required mechanical crushing of the resultant metal-laden slags from the first reduction while the bellow-powered copper smelts were about to create free-flowing slag that floated above the heavier metal (Chirikure 2018). Some North African innovations in copper smelting included roasting of sulfide-rich copper ores (to drive off the sulfur) before smelting the resultant copper matte, as well as the Egyptian use of their mouths to blow into reeds that were tipped with clay nozzles (Ogden 2000). In sub-Saharan Africa, roasting of copper ores and slag-tapping were practiced in the Democratic Republic of the Congo during the late 19th century, tempering clay crucibles with iron slag having been done in northern South Africa.
With regard to tin smelting, the precolonial process did not conform to the modern industrial two-stage process, where an initial stage involves mild reduction followed by further smelting under highly reducing conditions in the second stage. Instead, a nuanced one-stage process was employed in which conditions were manipulated to avoid the detrimental co-reduction of iron and tin (Miller and Hall 2008; Chirikure, Heimann, and Killick 2010). This was a compromise because more tin was lost to the slag, thereby reducing the metal output.
The constituent alloy produced in precolonial sub-Saharan Africa was bronze, and to a lesser extent, brass and steel. Precolonial gold–silver alloy production was mainly practiced in Egypt, Nubia, Ethiopia, and North Africa (Chirikure 2018). Sub-Saharan Africa blacksmiths were capable of producing hypereutectoid steel with variable carbon content; ferrite (up to 0.02 percent), cementite (6.67 percent) and ferrite (0.8 percent) (van der Merwe 1980; Miller 1992; Denbow and Miller 2007). In East Africa, there are reports of working cast iron which was decarburized to low-carbon steels in crucibles so that it could be forgeable (Kusimba, Killick, and Cresswell 1994; Kusimba and Killick 2003). While high-carbon steels must have been produced by the Swahili smiths in the first millennium ce, the possibility remains of importation of such crucible steel (Killick 2009; Chirikure 2015).
In Eurasia, bronze was probably discovered at an earlier date than the reduction of tin ores to metal through co-smelting copper ores with noticeable amounts of tin, leading to the production of unintentional low tin bronzes (Craddock 1995). The same pattern does not apply in sub-Saharan Africa. Instead, deliberate alloying to produce several low-tin and standard bronzes using tin mined principally in northern South Africa and Jos Plateau in Nigeria was carried out in several countries. The alloying was predominantly done by mixing already smelted tin and copper in ceramic crucibles that were further insulated in a cluster of large rocks to allow for the pumping of bellows, necessary for melting of these metals (Wagner and Gordon 1929; Bandama, Moffett, and Chirikure 2017). The melting temperatures for alloys of brass (930 degrees Celsius) and tin bronze (950 degrees Celsius) was very high and therefore required receptacles with sufficient mechanical stability at high temperatures. Accordingly, at KwaZulu Natal (South Africa), brass workers used sandstone crucibles (as opposed to the widely used ceramic crucibles) (Maggs and Miller 1995). Because zinc is very volatile, Eurasians typically worked brass in constricted (sometimes lidded) vessels in order to force the zinc fumes into the copper (Rehren 2003, 209; Martinon-Torres and Rehren 2014, 115). Poor brass research coverage in Africa makes it difficult to be categorical about African brass installations, but generally, the production of this alloy must have been limited to recycling and reworking of imported brass articles because no zinc deposits were exploited in sub-Saharan Africa prior to the 19th century.
Fashioning Metal into Objects: Smithing, Fabrication, and Casting
Nuances to the post smelting and melting metallurgical process were based on the type of metal, alloy, or end product anticipated. Regional variations of specific tasks also occurred in Africa. For iron, smithing and fabrication techniques appear to be less varied when compared to nonferrous ones. Shallow furnaces were typically employed to drive excess slag from smelted iron blooms, often accompanied by hammering with large hammerstones. Once the bloom was sufficiently cleaned, simple hammering techniques (hot and cold working, sometimes accompanied by annealing but without quenching) were major fabrication techniques for ferrous metallurgy. Fabrication for nonferrous metals also employed the same hammering techniques but casting and wire drawing were also added. While South and East Africa emphasized wire drawing, soldering and lost wax casting were practiced in West and North Africa as well as in Eurasia (Herbert 1984).
In Southern Africa, casting involved simple pouring of molten metal or alloys into shaped clay molds or prepared sand to produce ingots (such as rods, buns, and bars). The miniature hat-like (mu-Tsuku) ingot of the Lemba and Venda people, as well as the golf club-like (lerale) ingot of the Sotho–Pedi people appear to crown ingot casting in Southern Africa (Thompson 1949; Miller 1992, 2010). By contrast, the West African lost wax method used molds made of beeswax, which burned out after casting to reveal more complex artifacts (Herbert 1984). Generally, alloys of copper and tin (bronze) or copper and zinc (brass) are much easier to cast than copper alone because they melt at much lower temperatures than copper and generate fewer gases to cause blowholes and porosity in the finished products (Bandama 2013). The Akan gold workers in Ghana also produced impressive golden objects using the lost wax casting method (Garrand 1989).
Cline (1937) posits that wire drawing was mainly practiced in Southern, East, and North Africa. Beginning perhaps in the 10th century ce and throughout much of the second millennium, wire drawing appears to have been the principal fabrication method for nonferrous metallurgy in Southern Africa (Herbert 1984). Sites dating to this period in Zimbabwe, Zambia, South Africa, and Mozambique continue to exhibit quantities of these wires. This relatively simple but delicate technique was executed using pincers to pull the hammered end of wire through a draw plate (fastened to a tree) with different sizes of holes (Steel 1975). In some cases, it was the draw plate that was pulled as the pincers were fastened to a tree (Herbert 1984). Annealing after each pull and lubricating the plate hole with fat reduced shearing and produced less striation marks.
Consumption and Distribution of Metals
The African appetites for different metals have been far from straightforward, and the identification of local and regional patterns was key to successful itinerant trading. In Egypt, iron technology did not find root until late in the first millennium bc because bronze was preferable (Killick 2009). By contrast, the same metal was quickly adopted at the first opportunity in much of sub-Saharan Africa, with bronze and gold lagging behind. In sub-Saharan Africa, iron appears to have cut across both the utilitarian and the expressive spheres, and together with copper, they never lost favor even after the introduction of cuprous alloys and the noble metal (Bandama et al. 2018). Copper, “the red gold of Africa,” and its alloys found local meaning in much of sub-Saharan African communities and were therefore more preferable than gold, much to the delightful bewilderment of Eurasian traders and travelers (Herbert 1984).
As expected, iron and copper ingots and objects served as convenient stores of value and were often used as currency in some contexts. In West Africa, iron blooms were traded and kept as heirlooms, while iron hoes were a form of medium of exchange in parts of Southern Africa. In the parts of the latter region, copper ingots, such as the X- and H-shaped ones, served as currency for a long period (Swan 2007). Tin and bronze as well as other non-metallurgical objects also served as some form of currency, raising a question about how different modern comprehension of the concept of currency is from the precolonial one. For instance, by CE 1600, the Portuguese traveler Joao dos Santos reports that the “currency” at Sena and Tete consisted of small copper bars, small ingots of tin, colored beads on strings, and various kinds of cloth and gold (Axelson 1960). More significantly, the assigning of value in Africa has always been context- and time-specific. For instance, silver used to be more valuable than gold in Egypt at one point, but this situation later reversed (Chirikure 2018).
The Sociology and Spatiality of African Metallurgical Practice
One key feature of African metallurgy is that it resists homogenization, yet anthropologists who study the subject are more inclined to homogenize than to seek variations. The highly ritualized sub-Saharan iron smelting process carries the largest burden of homogenization by researchers. To some extent, ethnographic, ethnohistorical, and archaeological data have shown that in much of this region, iron smelting was considered ritually akin to the act of procreation and therefore was carried out away from or in seclusion from women and domestic contexts. Yet there were numerous exceptions, such as the Ndondondwane and Magogo of South Africa, Njanja and HlambaMlonga of Zimbabwe, Busanga of Ghana, and Barongo of Tanzania (Schimmin 1893; Maggs and Ward 1984; Herbert 1993; Schmidt 1996; Chirikure 2007, 2015; Swan 2007). Perhaps the need to capitalize on labor (from both women and children) was one of the major factors for relocating smelting precincts within domestic space. For instance, in some societies women were allowed in the smelting area and even participated in ore procurement and furnace construction, even though the actual smiths and smelters were male (Killick 1990; Herbert 1993; Kiriama 1993; Schmidt 1997). With alluvial deposits such as gold and tin ores, more women may have taken part because, as once suggested by Park (1799, 217–218) in the case of gold mining in Mandingo, women participated in the washing of alluvial ores because the act resembled cereal winnowing, which they were used to.
Large-scale metal production also made a case for looser application of taboos and proscriptions against women. All the same, a blanket application for all large-scale production situations is not possible, as shown by the case studies of the Bassar (Togo) and Babungo (Cameroon) iron industries where there was both maximum utilization of labor through the mobilization of women, children, and slaves in work (such as mining, charcoal preparation, as well as haulage of these materials to the furnace) and the upholding of rituals by just a few individuals supervising the smelting operations (Herbert 1993; de Barros 2000; Chirikure 2015). The Kwanyama of southern Angola are known to have included the whole family in the iron smelting process in which females also took turns with the pumping of bellows because of the need to meet increased demand (Angebauer 1927, 111). Beyond iron smelting, the Mafa (Cameroon) invited the whole family to witness rituals associated with the establishment of a new forge (Labouret 1931, 68) and in Kenya, some forges were located in private places for spiritual reasons, among other functional considerations (Kusimba 1996, 390). Cases of smithing while naked have also been reported (Jeffreys 1952, 152). Even with the normally less ritualized copper smelting, some communities in Burundi forbade the presence of women or strangers during either forging or wire drawing and the smiths were also supposed to refrain from sexual relations the night before work was undertaken (Herbert 1984, 41). This confirms that African social boundaries of metal working are difficult to define because of so much diversity. Technically, all iron workers could work copper, gold, tin, bronze, or brass, but there are contexts in which sociocultural factors prevented some groups from performing some tasks. For instance, the casting of cult brass images by Ogboni smiths among the Yoruba was a preserve for men past child-bearing age because the process was surrounded by libations, sacrifices, and other rites (Herbert 1984, 40).
Without ethnohistorical intervention, some nuances may have been lost because the most dominant means of incorporating gender into African smelting was through explicit sexual songs and dances (Blakely 2006, 104), and in some cases, ritual “medicines” were administered orally to the smelters or though placing of organic materials such as pieces of human afterbirth into the furnace, which do not leave recognizable traces in the archaeological record (McCosh 1979, 163). Nonetheless, examples of “small medicine holes” usually sunk into the floor of iron smelting furnaces can be encountered (Schmidt and Childs 1985; Rowlands and Warnier 1993).
African Metallurgical Innovations
The diversity of African metallurgical practices makes a case for a systematic search for innovations because, as argued by Kristiansen (2005), innovations are generally part of an ongoing process of refining routines and efficiency by adding new elements. In its minimal sense, innovation refers to attempts to put into practice an idea or process thought to be new to a community, and the term contrasts with invention, which is the first conception of that new idea or process (Kristiansen 2005, 151). Taken in this simplest sense, the list of African innovations becomes almost endless. From the still contested independent and simultaneous discovery of iron and copper metallurgy in West, Central, and East Africa to the creative use of sandstone crucibles for brass making in Southern Africa, African metallurgists appear to have been looking for new ways of winning metals from ores and transforming them into usable objects. The Egyptians roasted sulfide-contaminated copper ores to remove the sulfur and added a human element by literally blowing into the copper smelts with their mouths prior to the advent of various bellow types (Chirikure 2015). Further to the south, the people of Congo also roasted copper ores to drive off water and to partially crack the ores before the smelt. In Southern Africa in the second millennium CE, inception of tin and bronze production is also considered an innovation. Though the influence for the alloying of copper with tin may have come from Indian Ocean trade connections, the techniques and demand for this alloy largely remained local and regional (Bandama, Hall and Chirikure 2015).
Other innovations include slag-tapping for both iron and copper smelting processes in Southern Africa. The use of tall furnaces in which air was fed convectionally without forced draught power in sub-Saharan Africa is another innovation without direct evidence of transfer from outside the continent. The pairing of furnaces in order to maximize labor use by allowing one person to pump two bellows at the same time during periods of intensive metal production is another example of metallurgical innovation that has been reported in Southern Africa (Maggs 1982). Related to copper smelting is the innovative tempering of crucibles with crushed iron slag (Thondhlana 2012, 146–147). In East and West Africa, there are reports of tuyeres that were inserted deep into the furnace, as an intentional sacrifice to aid slagging (David et al. 1989). Previously, such deep tuyere protrusions were linked with the now challenged “preheating hypothesis” in which air passing through the tuyere would have been preheated before it entered the furnace, thereby ensuring very high temperatures and the production of high-carbon blooms (Avery and Schmidt 1979; Schmidt 1997). In mining contexts, the use of fire-setting to break rocks and narrow audits to provide lighting and ventilation in underground copper, tin, and gold mines is also another innovation (Summers 1969; van der Merwe and Scully 1971, 181–182). With metallurgical research having just scratched the African surface, it can be anticipated that new research will unearth even more novelties.
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