A Study on the History of Advances in Ancient Iron Making Based on Correlation of Oxides in Slag

A lot of slag was produced by ancient production processes such as smelting, melting, and refining. Iron slag has information that can be used to determine the characteristics of the site, the iron-making process and manufacturing date, but there is a limit to reading information through visual observation and nondestructive analysis. Various slag terms have been used depending on the location and characteristics, but it is necessary to use terms that have exact meaning and unity. Although many scientific analyses have been supplemented by archaeological theses, the iron-making trends of each period have not yet been systematically proven. This study reviewed the type of iron-making process used for 100 ancient slags. The slags were analyzed by XRF, revealing when it was formed and some of the detailed processes. XRD analysis was used to define and classify Tap slag, Bloom slag, and Ceramic-rich slag as relative concepts. From the Three Kingdoms Period to the Joseon Dynasty, the amount of temperature variation in the iron-making furnace decreased and the GAS reaction became uniform. It was observed that the amount of iron oxide remaining decreased and the proportion of ceramic-rich slag increased. The change in iron oxide content kept decreasing while the levels of refining, smelting, and melting were maintained, in that order. The results confirmed that advances in ancient iron-making technology can be interpreted based on a comparative review of the relative changes in iron oxide and silicon oxide content in slag.