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Blacksmith's Workshop

When we refer to iron processing here, we are speaking of a processing of metal working iron that is handed down to later generations. A fair number (dozens) of Yayoi Period-blacksmith workshops have been found that indicate the manufacturing of ironware. In one instance (Obarushimo Ruins, Nagasaki Prefecture), iron slag has been discovered in what seem to be the remains of a furnace that includes late Jomon Period remains.
The mid-Yayoi Period Akaide Ruins in the city of Kasuga, Fukuoka Prefecture, include a blacksmith's workshop with unfinished pieces of ironware. It has been confirmed that there is evidence that some of these iron fragments were melted in parts through the use of heat. From this we know that they were able to obtain rather high temperatures.

Iron-based fragments found in the Akaide Ruins

(source: “Yayoi Iron Culture and Its World” exhibit, Kitakyushu Municipal Museum of Archaeology)

If we look at the excavated examples, it's probably no mistake to say that iron processing began in the mid-Yayoi Period (around C.E. 1). However, there are no ruins that show metal working to have been done in an exacting way. For example, aside from furnaces there are no relics that correspond to bellows, iron scrap, iron slag, or metal working tools. Also, the results of studies done on iron slag show that most of it is metal worked slag whose principle element is iron ore. Metal working tools for working iron make their appearance from the mid-Kofun Period (5th century C.E.).

The Spread of Ironware

The century or so starting from the midpoint of the Yayoi Period (up to C.E. 100 or so) is a period of time in which ironware becomes widespread in northern Kyushu and stoneware declines. That said, there is wide regional variation in the spread of ironware; if we consider this from a national perspective, we see that the transition to ironware is mostly complete by the final quarter of the Yayoi Period (around C.E. 300).

A large quantity of iron materials are needed to make a large quantity of ironware. And if iron manufacturing is not yet taking place, then it has to be imported from the continent. According to the chapter of the Chinese chronicles (Wei Chih) dealing with the eastern barbarians, “These countries produce iron. They produce it in Wai [Korea], and Wo [Japan]. They use iron to buy things in the cities, as coins are used in China.” Based on this, it seems certain that iron was imported from the Korean Peninsula.

So, in what form was it imported? Though it is still not well understood, it is thought that the iron came in as iron ore, in masses of reduced iron like kera, in masses of pig iron, as forged iron scrap, and as iron tei (an iron plate of rectangular shape, it was used as a processed material or as coinage). Given that metal working was taking place from the mid- through late Yayoi Period, it may be that the materials used for that process were imported in the form of kera (a mass of pure iron) or iron tei. The technology for decarburezing pig iron (zuku-oroshi) is thought to date to a later period.