Decarbonizing Technique for Casting Iron to Make Wrought Iron Products in Northern Kyushu during the Yayoi Period

Abstract

Iron furnaces first appeared in western Japan at the end of the Middle Yayoi period, around the 1st century BC. At the same time, iron tools and weapons started to be produced in western Japan using iron raw materials imported from the continent. We discovered the first ever iron furnace that had been constructed on the surface with a clay wall and bellows at Karakami Site, Iki Island, Nagasaki Prefecture. At this site, flat iron and fragments of casting iron were found along with a large quantity of stone tools related to the site. Given the different structure of the furnace on the surface with the bellows along with the lack of iron slag and cut iron fragments, it is probable that this type of furnace was used for the production of wrought iron by decarbonizing from cast iron. This decarbonizing technique of making wrought iron from cast iron has been successfully demonstrated through experimental archeology. When comparing the forms of flat iron found in northern Kyushu during the Yayoi period, the same forms of flat iron are only found in the Itoshima area or lower Onga River area, but not in the Fukuoka Plains. In addition, pottery from the Itoshima area and lower Onga River area of the Middle Yayoi period is found at Karakami Site, although pottery from the Fukuoka Plains has not been found at this site through petrologic analysis. Therefore, it is believed that flat iron from wrought iron ingots produced by decarbonizing from cast iron in furnaces on the surface was exported from Karakami Site to the Itoshima area or the lower Ongagawa area. On the other hand, there was no trading of wrought iron ingots between Karakami Site of Iki Island and the Na area of the Fukuoka Plains.