greillade

Greillade was granulated or coarsely crushed iron ore, typically hematite or limonite, that had been calcined or roasted in air before being charged into a Catalan forge. The roasting process, carried out in open heaps or simple kilns, removed moisture and volatile compounds, making the ore more reactive and easier to reduce in the intense but localized heat of the forge's hearth. The term is now obsolete, surviving mainly in technical histories of medieval and early modern ironmaking in the Pyrenees and adjacent regions.

The Catalan process itself was a direct reduction method developed in Catalonia by the 13th century. Rather than producing molten iron that pooled in the furnace bottom, it yielded a spongy mass of metallic iron mixed with slag that could be drawn out, hammered, and reheated to expel remaining slag. Greillade's coarse, porous texture, created by thermal shock during roasting, accelerated slag formation and allowed the smith to work the bloom more easily than if raw ore had been used directly.

Preparation of greillade was labor-intensive. Ore was broken into fragments roughly the size of walnuts or smaller, then spread in shallow layers and heated. The roasting took several days; excessive heat could sinter the ore into hard masses, while insufficient heat left it weak and friable. Mills or hand-crushing removed only the largest lumps; no fine powder was produced, because fines would blow away in the forge draft and be lost. Batch sizes in a single roasting operation might reach several tons.

The greillade charge was mixed with charcoal in the Catalan hearth, a bowl-shaped depression typically 40 to 60 centimeters in diameter. Bellows provided forced draft; the reducing atmosphere converted iron oxides to metallic iron within a few hours. A skilled smith would know by sight and sound when the bloom was ready to extract. The process consumed roughly 2 to 3 parts charcoal for every part of iron produced, a ratio that shaped the economics of blast furnace development centuries later.

Greillade disappeared as blast furnaces became reliable and economical in the 16th and 17th centuries. Those furnaces could process raw ore efficiently at much larger scale, making hand roasting obsolete. The term itself is now confined to metallurgical scholarship and historical inventories of Catalan ironworks.