The Catalan Forge: Historical Iron Production Method

The Catalan Forge

The Catalan forge was the facility where iron was produced directly from ore using a reduction process known as the 'Catalan method'. This type of forge consisted of several key parts.

First, it had a furnace, the most important element of the process. This furnace typically had a truncated pyramid shape with three flat walls and one convex wall, designed to make the extraction of the final product easier. It was constructed from stone, often lined with refractory material. Inside, charcoal was layered with iron ore before the air nozzle (tuyere). Once lit, the furnace was left running for about 3 or 4 hours, reducing the ore at temperatures reaching approximately 1000 degrees Celsius. At the base of the furnace, a block of incandescent iron mixed with slag, known as a bloom (masser), was formed.

Secondly, it utilized a water trompe for the air supply. A channel fed water into a vertical tube which narrowed just after small holes allowed air entry. As the water fell down the tube, it drew in air via the Venturi effect. This air-water mixture entered a wind box below, where the air separated from the water. The water exited through a small hole at the bottom of the box, while the compressed air was forced through the tuyere directly into the heart of the furnace. This maintained the strong combustion of charcoal needed to keep the furnace at the desired 1000°C.

The Catalan forge was able to supply the amount of iron demanded by society until the Industrial Revolution. At that time, demand exceeded the supply capacity of these forges, leading to the development of larger production blast furnaces.

In Catalonia, however, large-scale steel production based on this method ultimately failed, primarily due to the lack of abundant local resources, particularly suitable coal (coke) and high-grade iron ore.

The Hammer

The water-powered hammer (martinet) was another essential component of the forge. Moved by the force of water, it was used for two main operations:

• To crush the iron ore before inserting it into the furnace, where it was layered with charcoal.
• To forge the hot bloom (masser) after extraction from the furnace. This hammering process expelled slag impurities and consolidated the metal, improving the mechanical qualities of the resulting wrought iron.

Resources and Products

The process required significant amounts of raw materials. The production of one ton of iron consumed roughly eight tons of ore and required a staggering thirty to fifty tons of charcoal. This highlights the critical importance of charcoal; forges were often located near large forests rather than necessarily close to iron deposits, as significant amounts of charcoal were consumed per ton of ore processed.

The wrought iron produced, depending on its final profile dimensions, received different names, such as vergalina (virgin iron, often used for nails), barrot (a large square bar, about three fingers wide and thick), and cairal (a square bar, about one finger thick). Profiles with a bright finish achieved by grinding were sometimes called 'silver iron'.

The operation of a forge was typically run by a master smith, known as a fargaire. Often, these were enterprises formed with partners, sometimes from other trades or professions, who provided the necessary capital investment.