Making Things from Metals
"Mu kre kee nga chiin? O tolԑԑlԑ pre naa pe jawala teeri na yirԑ pini. Pra ja na tͻͻrͻ woni gbleŋgaa nu."
"Did you know? Our grandfathers were scientists. They made metals from ores."
Every day we rely on useful things made from metals. People use metal tools at farm, in the kitchen and for many daily activities. Today metals are produced industrially and imported to West Africa. But in the recent past, the grandfathers made metals from local ores. They knew how to make tools and other things from iron (tɔɔnrɔ in Nafaanra), copper alloys like brass and bronze (swanyiɛfre), and gold (swanyiɛ).
Making metals from ores (rocks that contain metal elements) requires knowledge and skills that were handed down over many centuries. It requires knowledge about the sources and properties of minerals. It requires knowledge about how to separate the metal in an ore from its other elements. It requires knowing how to control fire in hot-burning furnaces. Making useful things from metals requires knowing how to shape metals through heating and hammering or casting them in molds. Archaeological evidence from the Banda area shows us that the grandfathers knew how to do all of these things. They were practicing scientists who experimented to find the right combinations of materials and conditions to make things from metals.
Metallurgy Was Practiced for Centuries in West Africa
The practice of making useful things from metals (metallurgy) goes back many centuries in West Africa. Archaeologists have found evidence of very early iron metallurgy associated with Nigeria’s Nok Culture, which dates back at least 2,500 years ago (550 BCE or before). In Ghana, some of the earliest evidence (so far) of people making their own iron comes from the Gambaga Escarpment (North East Region), where archaeologists have found evidence at Birimi that people made iron from ore by about 1,600 years ago (about 400 CE).
Archaeological sites in and around the Banda area show us that people living in the western Volta River basin over the last 1,000 years were smelting their own iron and using it to make tools, ornaments and other things. They were also making things from copper alloys (a combination of metals) through a process called lost wax casting. Although metals are not made in the area today, we have learned much about how Banda area people did so in the past through archaeology.
How Did They Make Iron?
The grandfathers made iron from locally abundant iron-rich rocks like laterite in a process known as smelting. They followed what scientists call a bloomery process. To do this, they exposed iron ore to high heat in a furnace using charcoal as a fuel. This caused iron to separate from other minerals in the ore and form a spongy mass (called the bloom). The bloom was refined and shaped into useful things through forging. The many steps (called an operational sequence) that people went through to make iron tools from ore required planning and cooperation among people.
In order to make metal, people first had to gather and process the needed materials. Mineral-rich rocks (ores) had to be mined and brought to the place where they would be processed into metal. Before smelting, large ore nodules had to be broken into smaller pieces using equipment like stone hammers and anvils. Smelters also needed large amounts of charcoal to fuel the smelting furnace. Therefore, wood had to be collected and made into charcoal. Because it takes roughly 100 kilograms of wood to make 10 kilograms of charcoal (10 to 1 ratio), people in the past had to take care not to over-harvest surrounding woodlands. Once wood was processed into charcoal, it also had to be carried to the place where the metal would be made.
The grandfathers made smelting furnaces from clay, which had to be mined and required them to know about clay-source quality. Smelters across West Africa built furnaces of different sizes, depending in part on how much ore they were smelting. The shape of their furnaces also varied, and this was a choice associated with networks of skilled people (called communities of practice) through which smelters learned their craft and ways of doing things (called a technological style; see also Making Things from Clay). To build a bloomery smelting furnace, men dug a shallow pit and built a thick conical shaft around it using clay. Tubes or pipes made of fired-clay (known as tuyeres), were inserted into holes at the base of the furnace. These pipes supplied oxygen to the fire inside the furnace. Sometimes tuyeres were attached to bellows, which were pumped to force air into the furnace in order to create a hotter fire.
When the furnace was completed and all materials collected, chunks of iron ore were placed inside the furnace, together with charcoal and other fuel. Temperature in the iron-smelting furnace had to be carefully controlled. It needed to be hot enough (about 1100-1200 degrees C) that unwanted elements (impurities) in the ore reached their melting point. At this point, the impurities turned to liquid and drained away, forming a by-product that scientists call slag. So long as the temperature in the furnace did not exceed about 1500 degrees C, iron from the ore would stay in a solid form called a bloom. But if temperatures in the furnace rose to more than 1538 degrees C (the melting point of iron), the iron would also turn to liquid and become brittle when it cooled. A successful outcome therefore depended on the smelter’s ability to control temperature inside the furnace, in part by adjusting the air flow using bellows. Depending on the size of the furnace and the quantity and quality of ore, the smelting process could take anywhere from a day to several days, a period throughout which the bellows might need to be pumped.
Scientists who have studied ancient metallurgy often describe the technological knowledge involved in smelting. But just as important were other kinds of knowledge and practices that ensured a successful smelt. Metalworkers took care throughout the process of gathering materials, building and firing the furnace to ensure good outcomes by making offerings (prɛ in Nafaanra) to ancestors and spirits, taking actions to protect metalworkers’ well being.
After smelting, skilled metal smiths turned the iron bloom into tools and other items through a process called forging. Forging refers to a process of repeated heating, hammering and then shaping iron to produce the desired object. Forges were very hot fires fueled by charcoal. Their intense heat was increased by pumping air into the fire through a pipe (tuyere) using bellows. Smiths sometimes roasted iron in the glowing charcoal to increase its carbon content. This made the iron stronger and more durable. When glowing hot, the iron was moved to a stone anvil where it was hammered with a heavy stone to help remove any remaining slag. With the slag removed and the iron solidified, the smith used hammers of stone and metal to shape the iron into a desired form, periodically reheating it in the fire to keep the metal soft enough to work. After they cooled, tools might be ground against a grinding or sharpening stone to form a sharp edge on a tool. Through these processes, smiths made a wide range of tools including knives and cutlasses (brɔfiɛn in Nafaanra), spears (chombo; pl. chomboolo), arrows (snini), sabres or swords (brɔfiɛŋunu; pl. brɔnfiɛnlɛ), and hoes (kagbaan; pl. kagbɛɛn) among other tools useful in farming, hunting, warfare and other activities. They also made ornaments like bracelets (kɛgbrɛ; pl. kɛgbrɛe) and rings.
While the direct work of smelting and forging was historically men’s work, women and children were probably involved as well, for example by collecting and processing needed raw materials (ore and charcoal).
Ancient Metalworking in the Banda Area
Archaeologists can learn about ancient metalworking in several ways: by studying the things that metalworkers made (for example tools, weapons or ornaments); by finding the tools and features they used to make those things (like anvil stones and furnaces); and by finding the by-products of making metal (slag).
The earliest iron smelting furnaces so far known in the wider Bono Region have been found around the ancient site of Begho, south of the Banda area. These date to the early centuries CE. In the Banda area, archaeologists have shown that metalworkers produced large amounts of iron and iron tools in the time between about 1200-1650 CE. Banda area sites of this time contain large quantities of iron slag, a by-product of smelting and forging iron, as well as occasional remains of furnaces and tuyeres. The amount of iron that metalworkers produced during this time was more than was needed locally. It seems likely that local people traded some of it, perhaps to northern areas where there were fewer trees (and therefore less wood to make charcoal) and it was therefore harder for people to produce their own iron.
Many sites in the Banda area have yielded traces of metalworking. However, the best evidence comes from the site of Ngre Kataa where in 2008 and 2009 archaeologists partially excavated a metallurgical workshop. Based on eight associated radiocarbon dates, we can say that the workshop was used by metalworkers between about 1350 and 1520 CE. A mound over one meter deep built up as metalworkers worked in the same place for many decades. Archaeologists call this workshop location “mound 6.” As archaeologists excavated the mound, they found equipment like anvil and grinding stones placed close to burned features created by the fires used to process iron and copper alloys. Fist-sized stones used as hammers were found lying close to the anvil and grinding stones, and the workshop had many sturdy-rimmed pottery jars placed close to burned features. Though we cannot say for certain, some of these pots may have been used as part of a bellows apparatus. Others may have held liquids used by metalworkers. Archaeologists also found broken tuyeres in several locations across the mound, as well as small crucibles used to melt copper alloys.
Archaeologists found iron and copper objects scattered throughout the mound 6 workshop deposits. Some were finished and others were in progress or broken. Many iron arrow points were found around the workshop, some seemingly finished, but perhaps never used since they were found in the place where they were being made. As the examples below show, smiths made arrows in different shapes, perhaps for different purposes. Other iron things found in the workshop area were blades of different shapes and sizes, spear points, bangles and finger rings. Smiths also made things in this workshop from copper alloys. Archaeologists found rings, wire and other small objects that were forged or cast from copper alloy, most of which was probably brass.
Archaeologists also found several clusters of carefully placed things that they interpret as shrine features. Their placement in the workshop reminds us that metalworking was a dangerous livelihood and that care was needed to protect the well-being of those involved. One small shrine cluster included an iron bangle, a smooth quartz pebble, two iron blades (one partial, one complete) and a small lost-wax-cast copper alloy twin figurine. Several similar figurines—some twinned, some single--were found at Kuulo Kataa. Based on similarities to figurines found elsewhere in regions northwest of Banda, archaeologists think that these were probably used in divination. A second mound 6 feature interpreted by archaeologists as a shrine cluster was a perforated pottery jar with a distinctively shaped mouth. It sat near several burned features that probably resulted from the heating of metals. A lid made from the pedestal base of another pot covered the perforated jar. Inside the jar were a number of cowrie shells.
These clusters were found in the middle levels of the workshop mound. A third much larger shrine cluster was found in upper mound levels. It overlaid equipment and features that had been used to process metals in earlier decades. This cluster extended across an area of several meters and included carefully placed iron bangles, pottery jars and lids, various sorts of metal tools, a miniature pair of iron manacles or shackles, an elephant tusk, the skull and jaw bones of a dog among other items. It is not clear whether mound 6 continued to be used as a workshop after this shrine in place, but it may be that when it was put in place, the location of metalworking activity moved away from this spot.
Archaeologists think that the work that happened at mound 6 was focused on forging and finishing metals. Based on the modest amount of slag found in the workshop, it seems likely that metalworkers during this time set up their smelting furnaces away from settlements, perhaps to lessen the distance that ore and charcoal had to be carried. The burned features found in the mound 6 workshop are therefore likely the traces of open fires rather than enclosed furnaces.
How Did They Make Things from Copper?
The skilled smiths who lived and worked at Ngre Kataa also made things from copper alloys. Copper is a relatively soft metal. It is combined with other metals (in an alloy) to make it stronger and more durable. Brass is made by combining copper with zinc and bronze is made by combining copper with tin.
Copper deposits are rare in West Africa and there are no sources anywhere close to Banda, so the smiths who worked at Ngre Kataa probably got their copper in the form of brass rods (ingots) through trade with people living along the Niger River. Some of the copper traded there came from mines in the Sahara and some of it came from across the Sahara. Camel caravans brought ingots of brass across the Sahara desert as illustrated by an archaeological site in eastern Mauritania called Ma’adin Ijafen. Here, in the 1960s, goods carried by an abandoned 11th-12th-century CE caravan were found among sand dunes and documented by an archaeologist. The caravan’s cargo included hundreds of 75 cm-long brass ingots, the chemistry of which suggests that they may have originated as far away as northwestern Europe. The workshop at Ngre Kataa dates to a century or two later, but small pieces of brass rod found in the mound 6 workshop, square in cross-section, resemble those found at Ma’adin Ijafen.
The smiths who worked at Ngre Kataa used imported brass to make a variety of ornaments including finger rings and ear rings. Some were made by twisting copper alloy wire. Others were made by heating and hammering the metal. But the presence of crucibles and finished cast objects suggest that these smiths also made copper-alloy objects by lost wax casting. In this process, an object is first made out of wax. The wax model is encased in a clay mold and allowed to dry. When the mold is dry, it is baked in a fire, causing the wax to melt and drain out through holes or tubes that the smith built into the mold. Meanwhile, the smith heats pieces of brass in containers called crucibles until the brass turns to liquid (becomes molten). Once the wax in the mold has melted and drained away--but while the clay mold is still hot--molten copper alloy is poured into the mold. The metal becomes solid as it cools. When fully cooled, the mold is broken open and the object finished by filing and polishing. It was through this lost wax casting technique that objects like the twinned figurine found as part of a small shrine feature in the mound 6 workshop were made.