A bloomery was an early style of furnace utilized for smelting iron. Bloomeries produced a porous substance called bloom, which was comprised of iron and slag, a byproduct of the smelting process that divided the metal elements from the nonmetal elements. They were primarily used in steelmaking and the production of wrought iron. In the modern era, bloomeries have been replaced by industrial furnaces called blast furnaces.
It is thought that the first bloomery was created around 3000 BC. At the time, however, those working in the field did not know what to do with smelted iron, and it wasn't until 1200 BC that iron was first widely utilized. When the Iron Age took hold of the Western world around that same time, it was largely possible because of the capabilities of the bloomery.
The physical structure of a bloomery contained a chimney, pipes called tuyeres, an aperture to remove the bloom, and, sometimes, an air- or gas-compressing device. The walls of the bloomery were comprised of some sort of heat-opposing substance, such as earth or stone. Some bloomeries did not contain an opening from which the bloom could be extracted, but instead required workers to overturn the bloomery itself and take the bloom from the top portion of the furnace.
When workers used a bloomery, they first preheated the unit by lighting charcoal. When the device had reached the appropriate temperature, iron ore and more charcoal were fed into the top part of the furnace. The charcoal produced carbon monoxide, which stayed trapped in the unit and facilitated the reduction of oxides in the iron ore without causing it to melt; this produced metallic iron. During the process, tiny specks of iron drifted to the bottom of the bloomery, and these bits become fused together and result in the slag. Steel was produced in bloomeries by altering the flow of air into the unit.
The bloom produced by a bloomery was traditionally used in a machine called a double hammer. The double hammer shaped metal through compressive pressure. Blooms or lumps of wrought iron to be hammered and shaped, commonly known as puddle balls, were placed inside. A set of large hammers moved in opposing directions on either side of the device, compressing the bloom or the puddle balls within the unit. This pressure rolled and shaped the bloom or puddle balls into metal.