Sukur Furnaces

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Introduction

Sukur is famous for its former iron industry, which is unique in its characteristics and therefore an essential topic for cultural heritage studies. On this page we describe the material culture related to smelting iron and the distribution of furnaces. We conclude with suggestions regarding the inventorization of furnaces.

The Sukur industry comprised both the production of iron and its distribution through a market that attracted buyers not only from their plains-dwelling neighbors but also from northerners, known to the Sukur as the Vuwa, a term referring to various northern peoples including no doubt the Kanuri of Borno. Although some of its neighbors were involved in various ways and degrees, Sukur’s committment to iron production and distribution was intensive, uniquely so among the peoples of the Mandara mountains, to the point that it can be described as village industry, one in which almost everyone, men and women, farmers and specialists were actively involved.

While other sources (David and Sterner 1995, 1996) describe the iron industry from an economic perspective, this page focuses on the technical means by which ore was transformed into metallic iron. Iron ore in the Mandara mountains takes the form of iron oxides in which iron atoms are combined with oxygen atoms and smaller quantities of other elements. The principal ore is magnetite (Fe3O4) which erodes out of the local granites, looking like a black sand. The ore is washed to separate it from the sandy matrix within which it is found.

The process by which iron oxide is reduced into its constituent parts is known as smelting (and not melting!). This takes place in the furnace where heat is applied to the ore in such a way as to separate its components into metallic iron (Fe), carbon monoxide (CO) and dioxide (CO2), the carbon coming from the charcoal with which it is mixed, and byproducts, principally silicates (Si) that contribute to the slag – glassy waste – which is formed during the smelt, and commonly discarded near furnaces.

Mandara mountains furnaces
There are three types of furnace in the Mandara mountains, all designed to exploit the region’s iron-rich magnetite ore (David 2010). Built up of daub (adobe) and usually built into or backed against a terrace, they are of bloomery type, which is to say that they do not achieve the temperatures over 1300℃ needed to melt the ore as happens in blast furnaces that produce high carbon pig iron. Bloomery furnaces instead produce various forms of iron blooms in which metallic iron is associated with charcoal fragments and slag. The Sukurian (and most common) type of furnace has a shaft about 1m tall and typically produced from 7 to 11 small blooms in a day. These  consisted mainly of low carbon (or mild) steel and wrought iron, with very little carbon. mixed with slag and charcoal. The much rarer free-standing Teleki-Banan furnace, never studied in action by archaeometallurgists, is in may ways a larger version of the Sukurian with a shaft around 160-170 cm tall. However, it is designed so that slag drains away from larger and more homogeneous, horseshoe-shaped iron blooms, of which perhaps three to five were produced in a day. The tall Mafan furnaces, with shafts in the 170-200 cm range, were worked by specialists. They can reach temperatures of over 1300 ℃ for brief periods and after many hours produce a bloom mass that contains a mixture of cast iron pellets, steel and wrought iron together with charcoal and slag. We infer that the Sukurian furnace is the oldest type with Mafan and Teleki-Banan furnaces separate innovations developed from the common stock.

All these furnaces are characterized by vertical shafts into which ore and charcoal are introduced through an upper opening, the charge hole, while blooms are removed through the lower opening, the shaft opening. Unlike other African bloomery furnaces into which air, providing the oxygen necessary for combustion and the achievement of high temperatures, is introduced from near the base, Mandara furnace hearths receive air from bellows located above the shaft. These propel air through a near vertical clay tube called a tuyere down to the base of the shaft where charcoal and ore meet fire and reduction of the ore takes place. The genius of Mandara furnaces is that they combined magnetite ore, which being relatively pure produces little slag, with tuyeres that, as the smelt progressed, melted at their tips, retreating upwards and in the process producing sufficient glassy slag to protect temporally the iron produced from being re-oxidized by the air forced down the tuyeres.

The Sukur furnace and its accessories

Smelting ceased in Sukur during the earlier 1960s as the market was flooded by industrial iron and scrap. By the time of our arrival In the 1990s only ruins and traces remained.

Ɗay Kərɓa’s furnace

This, the best preserved traditional furnace, attributed to a previous Ɗai Kərɓa, is located in Goeri subward of Gwassa near the house of Ndiho, the Tləduv title-holder who acted as our informant. Figure 1 shows this furnace after we had cleared away surface debris and collapsed and redeposited materials. Like other Sukur furnaces this is built into an agricultural terrace rather than, for example among the Cameroonian Plata, separately with subsequent incorporation into a terrace. Above the top of the shaft a bellows platform extends into the slope and from this level a daub shield was built up behind which the bellows were pumped. Ndiho is sitting in the bellows pumper's position. The tuyere port, at the top of the shaft, is not visible in this image.

DKfurnace

Figure 1. The Ɗai Kərɓa furnace seen after clearing in an image overexposed to reveal the medicine hole in thte floor of the shaft. The tuyere port at top of the shaft is not visible (7 Jan. 1993)...

There is a substantial thickness of daub around the back and sides of the furnace. As seen in Figure 2, the surviving parts stand 95 cm high, with the top of the lower shaft opening ca 40 cm and the charge hole 61-76 cm above the base. These are the dimensions of a furnace whose master smelter was of female ritual gender (gwat dəm), a topic discussed by David and Sterner (2009).

DKFurnPlan

Figure 2. A sketched reconstruction of the Ɗai Kərɓa furnace: frontal view and cross section. . .

The cross section of the furnace shows a number of features. The tuyere, of which only the top portion survived, hangs down into the shaft at an angle of ca 14º. Tuyere fragments are often found around furnaces, some showing vitrification and thinning by melting at the tip. They are constructed in two stages. First a pottery tube about 35 cm long and with a flaring rim is made. This serves as an armature (njak) over which the rest of the tuyere is built up of coarse daub containing rock fragments up to 7 mm in max dimension; a little finely chopped grass was probably added as tempering material. The tuyere bore is 4-5 cm in diameter. Its reconstructed original length, reaching down almost to the base of the shaft, is 97 cm. The tuyere was inserted through the lower shaft opening and up into the tuyere port (‘wai dlya, literally neck of furnace) where it was wedged into position with flakes of granite and plastered into place.

According to Ndiho the tuyere pointed directly at a hole at the base of the shaft, which had once held medicine. This was not plastered over, unlike three sets of three smaller holes, once also containing medicine, in the back and sides of the shaft. These were covered over with 1 - 2.5 cm of daub that extended upwards, lining the lower 50 cm of the shaft, including the underside and back of the arch of the lower shaft opening. It also extended forwards from this shaft opening onto smoother plaster on the front of the furnace. The plaster lining the shaft was extremely coarse, containing quartz and granite fragments up to 5 mm in size. It is called həranzan and is made of a brown-yellow dəghul clay (developed from rotting granitic regolith). The plaster on the furnace facade is smooth and contains cattle dung.

At the end of a day’s smelting the remains of the tuyere would be removed and a new one moulded over the reusable pottery armature and a stick before being left in front of the furnace to dry, perhaps benefitting from any residual heat though air temperature at the smelting time of year is likely to be in the 30℃ range even at night.

In Figure 2, the lower shaft opening is shown blocked with tuyere fragments, but other materials including rocks and potsherds were also used for this purpose. These could be easily removed and replaced as successive blooms were extracted in the course of a day’s smelt. Unlike Mafan furnaces where the lower shaft opening is closed with a thin wall of daub pierced to allow the venting of gases, gaps between the constituents of the blocking materials used for Sukurian furnaces allowed gases to escape.

No bellows survive from the smelting era; however they were functionally identical to those still used in forges (Fig. 3). Sitting on a rock, they consist of two small bowls with slightly everted rims encased in daub. Each bowl is pierced near the base, through which a ceramic nozzle passes delivering air into a short Y-shaped-shaped intermediary tube that feeds air down into the tuyere. Animal skins are tied around the rim of the bellows pots and the centre of each skin is usually attached by a short cord to a cross piece used to pump the skins up and down. There is no valve in the bellows-tuyere air delivery system. Instead the Venturi effect of rapid pumping (we timed one Mafa furnace master at over 900 beats a minute) sends small packets of air down the tuyere to the hearth.

Forge bellows

Figure 3. The bellows complex and forge hearth in a little-used Sukur forge. Here the bellows bowls, lacking their skins, are of enamelled metal rather than pottery. A forge tuyere lies flat and out of position on the surface of the hearth. The forge bellows and hearth complex is remarkably similar to that of larger and taller furnaces.

Sukur like other Mandara mountains furnaces are metaphorically female and the smelt is conceptually linked with the intake of foods via the charge hole (mouth), their digestion and nourishment of a fetus in the shaft (belly), a process of gestation that culminates in the delivery via the lower shaft opening (private parts) of a baby in the form of a bloom. This furnace has a daub projection described to us as a “nose” between the upper and lower shaft openings, in a position where one might rather expect an umbilicus.

The furnace had originally been located in an enclosure within which the smelters worked. A modern reconstruction is described below. A furnace takes about seven days to build with time allowed for drying. To prepare a whole furnace with enclosure takes about three weeks work mainly by the team that is to use it. It involves some excavation, terrace building, and the erection of a shelter roof. Experienced furnace masters, including at least one Hidi, might supervise two furnaces set side by side simultaneously.

Wutsi's furnace

In Devdagwa, Midala ward, another furnace is located close to the house of Bəlama Wutsi Midala. The present furnace is the second reconstruction. The first was used ca 1982 in Basil Davidson’s (1984) BBC documentary series Africa: the mastering  of a continent but subsequently deteriorated. About 1988 the Gongola (later Adamawa) State Arts Council arranged for it to be rebuilt for another smelt re-enactment, and this was again refurbished before 2008. Built three decades after smelting ceased, precise dimensions and details cannot be regarded as necessarily authentic.

Wutsi's furnacce

Figure 4. Wutsi's much rebuilt furnace and enclosure. (29 Feb. 2008)

The Wutsi furnace was also built into a supporting terrace and in general shape, shaft and openings, closely resembles the Ɗai Kərɓa furnace. Its shaft is that of a furnace master of male ritual gender (gwat malda), that is to say slightly wider and taller, four rather than three hand spans from the base of the shaft to the top of the charge hole (84 cm) --- although this is in fact only 8 cm more than Ɗay Kərɓa’s furnace. It has a nose and the shield behind which the bellows are pumped. However, the detailed form of the shield is not necessarily that of former Sukur furnaces. It was described by Wutsi as having shoulders and arms, emphasizing once again association with the human body.

Wutsi also stated, as did at least one other former ironmaster, that furnace shields were traditionally decorated with a finger-drawn X-design. This echoes the cowry and bead belts/necklaces that form part of the ceremonial costume worn by women and girls round their waists or necks. These are borrowed by male initiates on the last day of the Bər initiation festival and worn across the torso, forming an X-cross if the initiate can borrow two or more such items. Thus decoration on the furnace shield links it both to women and to male initiates. Because girls' initiations into womanhod are undertaken individually within the family (and because we failed to ask!), we do not know whether female initiates at any time wear such jewelry in bandolier fashion. However this may be, the association of such furnace decoration with females is entirely appropriate as is the status of the furnace as an initiate, ready to marry and then give birth to blooms/children.) Small clay models, often of cattle and mounted horsemen, that were often perched on furnace shields appear male-related and are accessories associated with the predominantly male smelters rather than the furnace itself.

During smelting the team worked in an enclosure some five meters in diameter delimited by rocks and protected from the sun by matting supported on wooden uprights that extended over the furnace and the bellows station (Fig. 4). Such enclosures were fairly standardized and incorporated the following features:

  • a daub basin (dugwuk) resting on a rock (see Fig. 4) located in front of the shaft opening. Ore was kept here before being charged.
  • a large bowl (gegyak) set into the lower platform and filled with water for dousing red hot blooms prised out of the shaft.
  • a wooden platter (garah) and a broom, both dipped in water, used to replace the red hot charcoal that fell out of the furnace when the bloom was removed.

Wutsi told us that the first bloom of the day was ready when the first charcoal had heated up properly, ore and charcoal had been added twice, and there had been a final addition of ore. The sound of the furnace -- suuaaah ! -- and a very white flame from the vent announced the readiness of the bloom to be removed. Old tuyeres blocking the shaft opening and supported by rocks and sherds were pulled away and the bloom prised out by two men, the furnace master directing. The bloom was immediately doused and red hot charcoal that fell out of the furnace put back in using the wooden platter and broom. Tuyeres and rocks were replaced across the shaft opening and the process began again.

At the end of a day’s smelting the remaining unconsumed charcoal was doused and used again after winnowing to remove dust and ash, and after picking through it to remove any fragments of iron. This mixture of ash, charcoal, slag and unreduced ore was also used for making plaster, such as is seen on the megalithic throne room, Bəgə, on the Patla ceremonial area outside the Hidi’s residence.

Other furnace remains

We found no other traditional furnace remains permitting comparable reconstructions. Many were weathered down to the base of the shaft and indeed in some cases, as when the remains occur in the bed of a sunken path, we are looking at a narrowing of the shaft below the original ground level (Fig. 5).

Furnace base

Figure 5. Basal remains of a furnace found in a millet field in Daza ward. The furnace was built into a slope rising towards the triangle (its hypoteneuse measures 30 cm). The lower shaft opening was to the bottom left of the image. We can see part of the medicine hole at the base of the fiurnace and layers of daub that connected the furnace to the terrace (no longer extant) into which it was built. (20 June 1996)

Furnace sacrifice and medicines

A season of smelting was always inaugurated by the sacrifice of a chicken by beating its head against the furnace which was instructed to “Take your food and make iron”. The carcass was then tossed out of the enclosure before being retrieved by children who brought it back to cook for all to share. A prayer was also said to god (zhigəla) , asking for a good outcome and protection from accidents, including fire, and any evil influences.

Three and only three medicines (ŋiwun dlya) were required for smelting. They are all wild plants but can be cultivated close to the house. These are rightfully called medicines because the furnace masters believe that they exercise specific effects on the smelt and its products, in the same manner that people take aspirin. The working of these medicines is however metaphorical rather than chemical.

After the plants had been chopped up and pounded into a paste, this was inserted into the ten holes and sealed in with clay.
  • Ŋiwun dlya is made of the exotic bəɗum plant (Figure 6), the cocoyam-like roots of which are used.  When the smelt is in progress the heat is said to cause liquid drops to form and to enter the furnace from the medicine holes. These help the iron to form into lumps like the roots of the plant.
  • Ŋiwun gwalay is an onion-like root that in a similar manner helps iron to form in smooth, bullet-like lumps (called gwalay). These are likely to be mild steel with a medium carbon content.
  • Ŋiwun gabə is another onion-like root from the hanzay gabə plant which has a protective function, militating against the dangers of gabə, loosely translatable as adultery but referring in particular to the danger caused by the presence of two men who have had sexual relations with the same woman.
  • Furnace medicine

Figure 6. The exotic flower of the bəɗum plant, the swollen roots of which are used as smelting medicine (14 June 1996).

Furnace distribution

Smelting at Sukur is far less bound up with ritual and metaphor than smelts undertaken elsewhere by specialists (David 2001). All or almost all able-bodied male Sukur and many women of the farmer caste (non-specialists) produced iron every year. Specialists could smelt but were generally too busy in their forges processing blooms into artifacts, especially currency bars (Fig. 7). According to informants, Sakun wards often had 30 to 50 furnaces. Smelting’s quasi-industrial scale meant that technical knowledge was public rather than the arcane province of specialists. Whereas women of childbearing age were often in the Mandara region and elsewhere in Africa not allowed near a furnace in order to avoid the clash of female and furnace fertilities, at Sukur only women actually menstruating could not come near. Otherwise women sometimes pumped the bellows, and furnaces could be built close to the furnace masters’ houses, perhaps even inside in the case of the Hidi.

Blooms and Bars

Figure 7. Sukur blooms and currency bars.

SukFurnMap

Figure 8. The distribution of furnaces in Sukur Sama as casually observed by us in 1992-2008. Furnaces are represented by a red fire symbol.

During our stays in Sukur we never attempted a census of furnace remains. Nonetheless we recorded them as and when we came across them (Figure 8 and Table 1). The map confirms the proximity of furnaces to houses but tells us little more. However, at Sukur we were constantly walking all over the plateau, to, around and through near and distant Sukur wards and on several occasions on to Damay, to Kurang, across the Təcini valley to Wula, north to Muduvu and Mefir Suku, west across the Nawu valley to the Mədləŋ massif and south to Tekassuw. Although we traveled usually on main paths, we also explored away from them. We can be certain that there are no furnaces hidden away in the bush. The presence of houses is the best predictor of furnaces nearby. To what extent this is true of Sukur furnaces on the plains we do not know. Certainly from in the late 1920s to the 1950s when it was safe to move down to the plains and land was available for the cost of clearing, Sukur were, we were told by plains ward heads, building furnaces on the plains in some numbers.

Table 1. The known distribution of Sukur Sama furnaces by ward, sub-ward and approximate GPS coordinates and of other furnaces noted in the vicinity.

Ward Sub-ward Furnace map label GPS N GPS E Date found Photos Notes; see furn.96.docx
Dungom Diɗa D1-7 ~10.741 ~13.567 93-02-13 none 7 furns spaced along outcrop facing ± W. S-most rep by enclosure only
Dungom Dungom Z1 ~10.738 ~13.569 96-06-21 960701-2 on/close to  path above Zavacera's house
Dungom Dungom Z2 ~10.739 ~13.569 96-06-21 none above Zavacera's nr top of Dunggom hill
Midala  Devdagwa Wutsi ~10.744 ~13.575 93-01-23 923620-1; 923817-9 Wutsi's furnace, western Devdagwa
Dalak ? Dalak 1 ~10.73 ~13.57 96-06-14 960507 Encl. between large rocks, facing Muva
Midala  Kuləsəgəi K1 ~10.742 ~13.573 96-06-16 930326-28 Base, on path leading N to Dzuvok
Dzuvok Dzuvok Məd ~10.743 ~13.575 93-02-17 none Mədlirəh hil NE, nr 3 aband. houses
Gwassa Goeri ƊayK ~10.744 ~13.571 93-01-23 923134-6; 923501-13;923601-06 Ɗay Kərɓa's: nr Ndiho Tləduv's , W side of path facing ~W
Gwasa Goeri Mz1 ~10.744 ~13.571 93-02-25 924524-5, 27-30 N slope of Muzi hill, Tlemuzi's F's furnace; 
Gwasa Goeri Mz2 ~10.744 ~13.571 93-02-25 none N slope of Muzi hill. Enclosure with stone for daub ore bowl 
Daza Dz 1 ~10.75 ~13.58 96-06-20 none By houses just above Catholic church
Daza  Dz 2 ~10.75 ~13.58 96-06-20 960433-34 Important furnace, located close to and a litle higher than Daza 1
Beyond Sukur
Mt Mədləŋ  Ndalmi N1 ~10.68 ~13.54 96-06-17 960426 on path down to stream flowing thru Ndalmi basin
Mt Mədləŋ  Ndalmi N2 ~10.68 ~13.54 96-06-17 none Mbaknyema's F's paired furnace enclosure near edge Nawu valley
Mt Mədləŋ  Ndalmi N3 ~10.68 ~13.54 96-06-17 960428-29 Usumana Aljim's paired furnace enclosure near edge Nawu valley
Muduvu Mud ~13.78 ~13.62 96-08-09 961217 Furnace w charge hole and tuyere port
Wula Wul ~10.74 ~13.63 96-07-19 960827-28 Furnace remains near Mazə Depda's house

While the Ndalmi furnaces are of Sukur type, made and used by Sukur who had migrated across the Nawu valley to the Mədləŋ Massif, it is worth noting that so far as we noted no obvious differences between Sukur furnaces and those we came across in Muduve Sama or at Wula.

The furnaces observed appear always to have been constructed near the base of a slope into which the furnace could be built, thus minimizing the labor required for construction of the bellows platform. A flat area, either natural or partially built up, extending away from the base of the shaft was needed for the enclosure of the lower platform, used for observation of the course of the smelt, charging ore and charcoal, and removal of blooms. Orientation of the furnace depended upon the slope, and not on cardinal points, prevailing wind direction, or any other factor that we are able to discern.

Cultural Landscape

Figure 9. The Sukur Cultural Landscape, Buffer Zone and surounding area. The Buffer Zone is delimited by green markers and the Cultural Landscape by red. Giwas are indicated, Daza being the only one that extends northwards outside the designated landscape.

Building a furnace inventory

An exhaustive catalog of material culture facilities is an essential part of heritage and conservation studies, and, given Sukur’s industrial history, an inventory of furnaces is a key element. As time is limited it would probably be best to focus the search on those parts of Sukur Sama that fall within the UNESCO cultural landscape and its buffer zone (Fig. 9). Minimally, at least two wards, one in upper and the other in lower Sukur Sama, should be thoroughly searched. We suggest Dalak and Gwafak, for which we have the least information. Any searches should of course be preceded by obtaining the agreement of ward heads, who will provide introductions to former smelters (though few iron masters will now survive). We also suggest enlisting the help of children by offering a small cash prize for every furnace, in whatever state of decay, they bring to your attention. When a furnace is located, record its GPS coordinates, take photographs and make notes on its characteristics, state of preservation and position in the landscape. Minimal removal of surface debris is OK, but leave any further clearance or digging to the archaeologists who will, we hope, follow up on your researches.

      

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