Iron is, for lack of a better word, good. If you haven’t spotted any iron around you today, it’s only because we’re so used to it that it has become essentially invisible. But before iron became ubiquitous in architecture, transportation, and elsewhere, the people of Earth had to make do without and hold their buildings and bridges up with rocks or trees or whatever. And so, tired of an ironless lifestyle, ancient man created the bloomery, with which they could smelt iron to their hearts content.
A Bloom of One’s Own
Consisting of a pit or chiminey (generally made of earth, clay, stone, or other heat-resistant material) with one or more pipes entering through the side walls near the base, a bloomery was the earliest manmade method of smelting iron. Preheated charcoal is used to “fire” iron ore inside the bloomery, and the pipes allow air to enter the furnace via natural draft or with assistance from bellows. The product of a bloomery is porous iron and slag, known as “bloom.” The so-called “sponge iron” that results from the process can be further forged to create wrought iron.
Not coincidentally, the development and widespread use of the bloomery ushered in the Iron Age. Earlier samples of processed iron do exist, but these artefacts have been identified as meteoric iron, which required no smelting, or happy accidents produced in bronze smelting processes.
A History of Bloomery
The earliest archaeological evidence of the use of bloomeries comes from East Africa, where bloomery-smelted iron tools have been dated to 1000 to 500 BCE. In sub-Saharan Africa, Forged iron tools dating back to 500 BCE have been found amongst relics from the highly advanced and mysterious Nok culture.
In Europe, the first bloomeries were small by necessity, capable of smelting only about 1 kg of iron at a time because they simply could not be built any bigger at the time. By the 14th century BCE, large bloomeries with capacities up to 300 kg had been developed. Some even used waterwheels to power their bellows.
At a larger scale, bloomeries expose iron ore to burning charcoal for longer. Combined with the more powerful air blast required to adequate heat the charcoal in these larger chambers, this often led to the accidental production of pig iron. This pig iron was naught but a waste product for roughly a century, until the arrival of the blast furnace, which enabled smelters to oxidize pig iron and turn it into cast iron, iron, or steel.
Eventually, the bloomery would be replaced for nearly all smelting processes by the blast furnace. Developed in China in the 5th century BCE, the blast furnace did not make its way to the West until the 15th century CE. It was long thought that the ancient Chinese did not use bloomeries, and instead went straight to blast furnacin’. However, recent evidence suggests that bloomeries were in use in China as early as 800 BCE, having migrated eastward from Europe.