I am going to start off this post with a pretty long quote from John Thornton in Africa and Africans in the making of the Atlantic World, 1400-1680 (pp 45-48). Please bear with me.

We can begin to see the complexities of the trade if we look at the trade in metals, and particularly iron, for iron was surely the best example of a commodity that was imported and could be used in tools and one where technique is essential to producing quality. The Portuguese exported little iron to Africa*, perhaps because they felt obliged to honor papal injunctions against selling materials with potential military value to infidels. However, Christian Kongo received little Portuguese iron either, so the more likely reason was that they produced little themselves and could not make a good profit exporting it. The Dutch, with access to good German and Scandinavian sources, and the English, with iron of their own, pioneered the sale of iron into Africa, iron bars already being prominent in the gifts that van den Broecke gave out in 1605.^4 Iron appears in Dutch trade lists of the seventeenth century as useful in every part of Africa, and they were sure to bring considerable quantities each year. Based on French and English trading company statistics, Curtin has estimated that Senegambia imported something on the order of 150 tons of European iron every year by the last half of the seventeenth century, although this figure is probably higher than earlier quantities.^5

But Africa was an iron-producing part of the world, and Senegambia was already being served by producers in Futa Jallon (and perhaps also by some poor-quality local iron)** at the time the Portuguese arrived.^6 Indeed, the Portuguese bought iron in Sierra Leone to sell in Senegambia and other points, as the books of the ship Santiago, sailing this route in 1526, clearly show.^7 But European trade with Senegambia in iron later on was not simply an attempt to compete with other West African producers in fulfilling the needs of an iron-poor region. Instead, the iron trade was more complicated.

The peculiarities of African iron production that made European iron attractive come, perhaps, from its earliest years. According to recent work on ancient African ironworking, the technology was developed by 600 b.c. or even earlier on the Sudanese fringe of the emerging Sahara desert, perhaps as a result of discoveries made in the copper-producing areas of the desert north of modern Nigeria. Because this was a fuel-poor environment, African iron workers developed methods to conserve fuel, of which the most important was devising a system to preheat the air blast that entered the furnace, which prefigured techniques used in Europe only in the nineteenth century. This not only saved fuel, but it allowed Africans to produce an amazingly good-quality steel - perhaps the best steel in the world of the time, and certainly equal to or even better than the steel produced in early modern Europe.^8 ***

Certainly research into the quality of metal produced by African foundries in West Africa in modern times and recent archaeology suggest that African steel was equal to that made anywhere in the fifteenth century.^9 But African steel still required considerable quantities of wood, and this was not always available, which meant that increasingly the best ironwork was done on the northern edge of the rain forest where there was a conjunction of wood supplies and iron ore (as well as abundant waterborne transportation). This sometimes made iron expensive in regions like Senegambia that were located some distance from the centers of reduction. As a result, European iron, even though of poorer quality,might be competitive in price and could be employed for those uses that did not require the qualities of steel.^10

But even if its price were competitive, one should not 1magme that imported iron came particularly close to fulfilling even the Senegambian needs for iron before 1680. According to Curtin's estimates, annual Senegambian imports of iron in 1680 amounted to 150 tons and was probably less in the half-century earlier. Thus iron would go to serve the needs of what might be a rather restricted iron-using population, along the coast north of the Gambia and inland along the Senegal to approximately Futa Tooro, where a local industry reduced the need for imported stocks. Curtin notes, in fact, that traders found little market for imported iron on the upper reaches of both rivers before the middle of the eighteenth century.^11

If we assume that each household had a minimum tool kit composed of a hoe, axe, large knife (machete or cutlass for clearing fields), smaller knives for cutting, and some arrowheads and spears for hunting (excluding for the moment military uses), then we can estimate that each household owned approximately two kilograms of iron at a time, which required replacement every two years (for the locally produced iron; lower-quality, imported iron needed biannual or even triannual replacement), and thus each household had an annual consumption of one kilogram of iron per annum.^12 If we accept that this restricted coastal region had a total population in 1650 of about 1.5 million, organized into perhaps 300,000 households, then these households require ~300 tons of local iron per year. But if they used imported iron (at the higher replacement rate) they would need at least 1,200 tons to meet their needs. Thus, imports could probably only have met about 10-15 percent of their needs.

These estimates of consumption are low, assuming minimum household consumption, and completely exclude military uses, one of the most important additional uses of iron. For example, the average Senegambian horseman, according to descriptions of the late sixteenth century, carried a sword, a broad-bladed spear, and seven or eight smaller throwing spears, and his horse and saddle also required a small amount of iron - in all perhaps two kilograms. Thus a unit of 500 horse by itself used as much as a ton of iron, with a higher annual replacement because some supplies were expended before wearing out (such as throwing spears, which might, for this reason, be made of inferior iron from the imports), and even according to conservative estimates of cavalry forces, the perhaps 15,000 horsemen of the coastal and lower rivers region required thirty tons of iron - not to mention the numerous infantry, some of whose weapons must be considered in the earlier estimates of household consumption, but who probably demanded ten or twenty more tons total.

But if European iron was not simply to fill the needs of an iron-poor region, and surely not to replace poor-quality iron with better-quality metal (if anything, as we have seen, the relationship was the reverse)****, then European iron clearly played a more complex role. Thus, Africans in Senegambia and elsewhere bought cheap European iron in bars (perhaps the most common form of purchase) but they also bought high quality steel swords, which were certainly used in their finished form. Africans could, of course, have made their own swords, for they possessed both the skills and the quality metal, but no doubt the imported sword was also an item of prestige whose value was not simply counted by its utility as a weapon. This might well explain why archaeologists found a European sword in a burial site at Rao that must have been purchased (through the trans-Saharan trade) in the twelfth or thirteenth century. The distance this sword must have traveled was far from simply being a measure of its utility.

Now, this is a broadly accurate overview, but there are a few aspects that I would quibble with (which I have noted with asterisks).

But, I'm running out of characters, so I'll cover them in a following post.

(edit- added asterisks to denote one more point for correction)