The Forges of an Ancient Capital in what was once Sabi, the final capital of the Baekje Kingdom (538–660 CE), archaeologists have uncovered evidence of a sophisticated iron and steel industry. Centered around sites like Gwanbuk-ri, the location of the royal palace, these facilities were not simple forges but organized production centers.%%CITE_1%%%%CITE_2%% The furnaces themselves were compact, semi-subterranean structures built from clay, sand, and organic binders like straw.%%CITE_3%% This design allowed for efficient heat containment, an important factor in their advanced metallurgical processes.
The technology employed was a direct reduction method, also known as a bloomery process. Inside the clay furnace, iron ore was layered with charcoal, which served as both the fuel and the source of carbon monoxide needed for chemical reduction. The entire process occurs below the melting point of pure iron (1538°C), meaning the metal never became fully liquid. Instead, it formed a spongy, porous mass called a bloom, which was a mixture of solid iron particles and molten waste products, or slag. This bloom was then hammered by smiths to compact the iron and expel the remaining slag, a physically demanding process that produced refined wrought iron and steel.
The Science of Baekje Steel
The secret to Baekje's advanced iron-making was temperature control. To reach the operational temperatures of 1100–1300°C needed for the process, and peak temperatures exceeding 1,400°C in the reaction zone, a constant and powerful flow of air was essential. This was supplied by a powerful bellows system, which pumped air through a clay pipe called a tuyère into the base of the furnace. The forced oxygen supply dramatically increased the charcoal's combustion temperature, creating an intensely hot zone where the reduction of iron ore to metallic iron occurred.
Scientific analysis of the slag, the glassy waste product of smelting, shows this ancient technology. Composed primarily of fayalite (Fe2SiO4) and wüstite (FeO), the specific mineral makeup of the slag confirms the high operating temperatures. Some slag samples show a CaO/SiO2 ratio greater than 0.4, indicating that Baekje smiths were intentionally adding limestone as a flux. This flux lowered the melting point of the ore's impurities, allowing the slag to become more fluid and separate more effectively from the iron bloom. Baekje artisans also mastered steel production, creating higher-carbon metal through carburization and employing heat-treatment techniques like quenching to produce hard, durable tools and weapons.