Smithing Processes Based on Hammer Scale Excavated from the Third- to Fourth-Century Ancient Iron-Making Sites of the Korean Peninsula.

The by-products of iron smelting and smithing include slag, flake hammer scale, and spheroidal hammer scale. The analysis of such iron-making by-products reveals critical information regarding the development of iron culture and the process characteristics. Using a metallographic microscope, SEM-EDS, and Raman micro-spectroscopy, we investigated the manufacturing process by examining the microstructure and determining the composition of the flake hammer scale and spheroidal hammer scale excavated from Korean Peninsula sites of iron manufacture during the Proto-Three Kingdoms Period, in the third and fourth centuries CE. Microstructure analysis confirmed that as the process progressed, the flake hammer scale's thickness decreased owing to forging, which flattened the structure. Additionally, three layers were observed, with the surface layer identified as hematite (FeO), the middle layer identified as magnetite (FeO), and the inner layer identified as wüstite (FeO). The analysis of hammer scales revealed that the forging process to create iron bars required repeated working, following a refining process to remove impurities, confirming the division of labor in the smithing process. Correspondingly, the smithing process stages can be deduced from the structural shape and thickness of the hammer scale produced during the iron manufacturing process. Thus, the findings of this study are expected to be invaluable in furthering our understanding of the smithing process in detail, through future research on hammer scale.