Bloomery

A bloomery is a type of furnace used for smelting iron from ore by direct reduction with charcoal. In a bloomery, iron ore is reduced to metallic iron in a solid state, producing a spongy mass called a bloom that contains iron and slag. Unlike modern blast furnaces, bloomery furnaces do not melt ore; the product is then worked by hammering to consolidate.

Construction and operation: A bloomery is typically a small shaft furnace built of clay, brick, stone, or earth, with a hearth at the bottom and a means of delivering air—such as a tuyere or hand-operated bellows. Air flow is limited to maintain reducing conditions. Ore and charcoal are loaded in layers, and as combustion proceeds, iron oxides are reduced by carbon monoxide and hydrogen to metallic iron. Slag forms as a separate layer and is removed. The bloom is periodically extracted and hammered to expel slag and weld iron grains.

Output and applications: Bloomeries generally produce tens of kilograms of iron per day, suitable for local toolmaking and weapons. They operate at lower temperatures than blast furnaces and are geared to small-scale, seasonal production. The iron produced can be worked into wrought iron; with additional smithing practices, it may be converted toward steel.

History and significance: Bloomery furnaces were widespread in Europe, Africa, the Middle East, and Asia from the Iron Age onward and remained common in some regions into the early modern period. They were eventually supplanted by coke-fired blast furnaces and more continuous ironmaking technologies. Archaeological remains—such as tuyères, hearths, and slag heaps—provide evidence of bloomery use.