Hydraulic forges: still living vestiges of our iron and steel past

In the previous post we analyzed the first of the two traditional ways of processing iron ore into metal, that of the mountain forges or haizeolas. In this new installment we will study the other traditional method: the hydraulic forges, a much more evolved procedure than the previous one, more modern in time, and better known, but which we cannot yet consider fully industrial.

By traditional iron and steel industry we mean the iron and steel industry prior to the implementation of the blast furnace in the 19th century, which is when we can properly speak of industrial iron and steel industry. Traditional steelmaking is based on the reduction of high quality iron ore (direct method), while modern industrial steelmaking is based on the melting of ore, usually of inferior quality, to obtain an intermediate material, pig iron (indirect method).

?

The first hydraulic forges

Although in other areas, such as Catalonia, the references are much earlier, in Euskal Herria, the oldest mentions of forges moved by the action of river water date from the end of the 13th century. For a period of time, the old haizeolas and the new forges would coexist in the same space, although with time, the latter would end up imposing themselves, until they were replaced, in turn, by the modern blast furnaces of an industrial nature, in the first half of the 19th century.

?

Operation

Both in the haizeolas and in the hydraulic forges, the resulting metal was obtained from the chemical reaction that took place inside the "low" furnace, or reduction furnace, in which charcoal and high quality iron ore, raw materials, very abundant in our territory, had been previously introduced. From this furnace, purified iron was extracted, leaving the slag as residual material. The iron sponge obtained (agoa), however, still had to be subjected to a new phase of purification: forging.

Not all the metal obtained was the same. Traditionally, we distinguish between soft iron, with a lower carbon content and more malleable, and steel, with a higher carbon content and greater hardness.

The great innovation of the hydraulic forges with respect to the mountain forges is that they used the driving force of the current of the rivers to move the two essential elements in the work: the hammer or mallet that hits the iron already processed and the bellows to blow air into the furnace. In the haizeolas, all the effort was manual.

The complex engineering work necessary to take advantage of the hydraulic force gave rise to some very characteristic facilities, the forges, the remains of which still dot our geography.

?

Parts of a forge

In its basic design, a forge should have at least the following elements:

- The dam or weir: This is the first element of the whole. It was used to impound water to facilitate a controlled flow to the forge's facilities. They were originally built in wood and later in stone. Since the end of the 17th century, arched dams have been characteristic of our territory.

- The canal: The water was diverted to the forge along a canal or ditch that gained height.

- The antepara and the hydraulic tunnel: This channel flowed into the antepara, or elevated reservoir under which the hydraulic tunnel was located, built parallel to the forge workshop. In this tunnel were the wheels that transmitted the power, by means of axles, to the interior of the forge building.

- The workshop: This was the place where the work was done. The axles fixed to the wheels crossed the wall of the workshop and continuously drove the two fundamental elements inside the forge workshop: the mallet or hammer that struck the iron extracted from the furnace by the forgers, and the bellows, which injected the air necessary for the temperature inside the furnace to reach the desired degree.

- The warehouses: Spaces where the large quantities of iron ore and charcoal, necessary for the combustion process, were stored.

?

Major and minor forges

A last important distinction is the one that differentiated between major and minor forges. In the former, the first stage in the transformation of the ore was carried out, that is to say, the phases described so far. The smaller forges reduced and thinned the billets produced in the larger mills, reddening them to make them more malleable and turn them into bars or semi-finished iron products. These facilities, also called tiraderas or martinetes, were smaller in size.

The decline of a centuries-old activity

Since their appearance in the Basque lands, towards the end of the Middle Ages and throughout the Modern Age, the hydraulic forges dominated the iron and steel production in our land. There were hundreds of them, especially in the territories of Bizkaia and Gipuzkoa. Their remains in the form of dams, canals or ruins of workshops and warehouses, are still scattered throughout the geography. Some have reached our days in relatively good condition or have been recovered to the point of being visitable, even being able to see them in operation. The forges of El Pobal, in Muskiz (Bizkaia) or Mirandaola, in Legazpi (Gipuzkoa) are good examples of this enhancement of our cultural past.

With the appearance of the first blast furnaces in the first half of the 19th century, the modest forges began an unstoppable decline, unable to compete with the new large-scale iron and steel technology resulting from the industrial revolution.