It is difficult to know exactly when and where iron began to be worked historically, although it seems that its use spread from 1200 BC onwards, more or less simultaneously, from various areas: the Middle East, India and the Eastern Mediterranean. To find the first evidence of its use in the Iberian Peninsula and the Basque Country, however, we will have to wait until the 8th century BC.
In the absence of greater technological capacity, these ancient iron cultures needed ore with a high iron content, which they reduced in simple furnaces dug out of the ground. This rudimentary system continued to be used, without too many modifications, for more than 2000 years, more or less until the end of the Middle Ages, when hydraulic forges, which were much more efficient, began to be used throughout our geography.
What the haizeolas were like
As we have said, this primitive iron smelting system did not evolve much from Antiquity until the end of the 14th century or the beginning of the 15th century. In the Basque Country, this type of mountain forge is known as haizeolak (air forges).
A haizeola was no more than a hole of about 30 to 50 cm, dug in the ground, covered by a stone elevation that could reach a height of one or one and a half metres. Its inner diameter could be between 50 and 70 cm. Holes were drilled at different heights to facilitate ventilation, probably induced by bellows operated by the forgers. Basically, the idea was to melt high-purity iron mixed with charcoal. As is to be expected, haizeolas tended to be built in places where these two raw materials were plentiful.
Production process
The first step was, logically, to obtain the raw materials involved in the process. As we saw in the previous chapter of this series, in our territory, and more specifically in the mining valleys of western Bizkaia, iron was extracted, most of the time, in the open air, without the effort of having to build underground galleries. The ore with the highest metal content, as mentioned above, was generally used.
This ore was not introduced directly into the furnace, but first had to be subjected to preliminary treatments such as roasting and crushing, processes that sought to make the iron melt more easily once it had been subjected to the high temperatures of the furnace.
At the same time, it was necessary to prepare the sufficient quantity of charcoal needed for the smelting process inside the furnace, as it is estimated that, for each kilogram of iron obtained, around one hundred kilograms of charcoal were needed. The charcoal production process in traditional mountain charcoal bunkers (txondorrak) was also carried out in the vicinity of the haizeolas.
The next step was to charge the furnace of the haizeola with alternating layers of iron and charcoal, or with a ready-made mixture of both. Once the fuel was lit, the action of the heat first produced a spongy mass (agoa), formed by the iron and its slag, which had to be progressively separated. Once the necessary temperature was reached, a large part of this slag became sufficiently fluid to be drained out of the furnace.
Once the resulting product had been extracted from the haizeola, it was subjected in situ to a first phase of ‘preforging’, which consisted of beating the mass to separate the slag that still remained in it, which also helped the metal to acquire a better consistency. While the metal was still hot, it was time to give the resulting iron the appropriate shape (bars or ingots), to be transported to nearby towns. Here, the final forging would take place, which would further refine the metal until it reached the necessary quality to be used in the manufacture of tools, weapons, anchors, or whatever.
Historical importance
The simplicity and fragility of these structures have meant that none of them have survived to the present day. Archaeological studies do, however, reveal interesting data about this activity, which has been so important and so closely linked to our history. Deposits of slag mixed with remains of charcoal have made it possible to identify the location of a large number of furnaces of this type. It has been possible to deduce shapes, dimensions and construction materials. We know that at some sites structures were superimposed on each other over long periods of time, even centuries. In some cases, several sets of complementary furnaces have been found, which supports the hypothesis that several stages of the process were carried out on the same site: roasting, reduction in the haizeola furnace and even the first forging.
This brings us to the end of this chapter dedicated to the earliest Basque iron and steel activity. The process of transforming iron ore into haizeolas has lasted much longer than any other, despite its simplicity and rudimentary nature. Compared to the approximately four centuries of the heyday of the hydraulic forges or the scarce 150 years in which modern blast furnaces have dominated our industrial landscape, the humble mountain furnaces effectively fulfilled their function for more than two thousand years. Knowledge of this remote past is essential to understand our subsequent evolution as a people linked to industry and iron. The haizeolas are elements of our heritage, still largely unknown to the general public, but which must be highlighted.