In this paper, we present the results of isotopic analyses of more than 600 bronze objects from the Bronze Age and Early Iron Age in Korea. The results of our analyses show that bronze objects belonging to the Lute-shaped Bronze Dagger Culture are all ternary alloys of copper, tin, and lead, mixed with other minor elements. The non-uniformity of their composition indicates the existence of several separate bronze industries at that time. While most of them consist of around 80% copper, 10% tin, and 10% lead, there are no clear differences in composition ratios amongst different types.
Bronze objects that belong to the succeeding Slender Bronze Dagger Culture are either copper-tin-lead ternary alloys or copper-tin binary alloys. Their metal compositions and ratios match the descriptions of the “six levels in metallurgy (jin you liu qi, 金有六齊)” discussed in “The Artificers Record (Kaogongji, 考工記)” chapter in the “Rites of Zhou (Zhouli, 周禮)”. This not only demonstrates that the bronze casting technology in Korea at that time was comparable to that of China, where the most advanced bronze technologies were pioneered in the region, but also indicates that bronze wares were made and used as daily objects for practical use.
By the following Proto-Three Kingdoms period, where bronze manufacturing and usage declined, bronze objects belonging to Slender Bronze Dagger Culture saw their tin content decreased while that of lead increased. Some minor elements such as arsenic and antimony were also present in these bronze objects. These changes are also evident amongst contemporary bronze objects in China, such as Wu Zhu coins (五銖).
In summary, bronze casting technique was fully developed with the appearance of Lute-shaped Bronze Dagger Culture in Korea. The emergence of the subsequent Slender Bronze Dagger Culture showed a further advancement of bronze technology in Korea, not only indicated by increased tin content and decreased lead content, but also differential composition ratios according to the types of wares. In the following Proto-Three Kingdoms period, decreased tin content with increased lead content amongst bronze objects is evident.