Ōshimizu B and Sawairi B Sites, Shinchi Town, Fukushima Prefecture

Discovery of iron smelting furnaces of the Heian period

Ōshimizu B and Sawairi B are sites related to iron manufacture of the Heian period (mid-ninth century). Excavations were carried out there in 2012 in conjunction with construction of the Jōban Expressway, considered a vital road for the reconstruction.

The sites are located atop hills extending eastward from Mt. Karō in the Hamadōri region in eastern Fukushima prefecture, where furnaces for making iron using iron sand as ore were found.

Two types of smelting furnaces and a charcoal kiln

In the Ancient period there were two types of furnace, a chimney-shaped furnace resembling an overturned bucket, and a box-shaped furnace similar to a bathtub, and while there is held to be a chronological difference between the types, one characteristic of the northern part of Hamadōri region of Fukushima is the presence of both types in the same area and even at the same time, as at the Ōshimizu B and Sawairi B sites.

As pig iron, which is high in carbon content, was ascertained for both types of furnace, it is thought that the same quality of iron was being produced despite the difference in furnace type.

Also, a climbing kiln built in the form of a tunnel dug into a slope, with a firing chamber 5 m in length (9 m overall including the work area) and 1.5 m wide was found. This is thought to have been used as a kiln for making charcoal that was used as fuel in the smelting. In addition, pits where clay was quarried were found as well. (Yoshida//Hideyuki)

Box-shaped furnace

This was found at the Ōshimizu B site. The furnace made from clay was at the dark central portion. The square pit to the rear is where the foot-operated bellows was set up.

Chimney-shaped furnace

This was found at the Sawairi B site. The dark part at center was the furnace, with the bellows in the rectangular pit to the rear, while to the front was a work area.

Artist's reconstructions of iron-smelting furnaces (top, box-shaped furnace; bottom, chimney-shaped furnace; illustrations by Suda Hiroyuki)

Both have foot-operated bellows as the mechanism for pumping air. At the far end from the bellows, for the box-shaped furnace there were more than 10 tuyeres (bellows nozzles) with interior diameters of 3 cm, and for the chimney-shaped furnace a single wind pipe of 7 cm interior diameter, which supplied air for the operations.

Recovered artifacts

At upper right is a Haji ware dish recovered from the slag heap at the Ōshimizu B site. At bottom to the left is the wind pipe for supplying air to the chimney-shaped furnace at the Sawairi B site, while at right is a fragment of the wall of the box-shaped furnace at the Ōshimizu B site. The pipe-shaped protuberances are the tuyeres (nozzles). The size of the tuyeres and the wind pipe are completely different.