Sueki (unglazed ware) (須恵器)

Sueki is earthenware which was produced during periods from Kofun to Heian in Japan. The color is blue-gray and it is hard. It is easily-distinguishable from the contemporary Haji ware by its color and quality, but some are intermediate between the two. Sueki was brought to Japan from the south of Korean Peninsula and was treated as more luxurious pottery than Haji pottery.

Terms and characteristics

The kanji for earthenware '陶器' was read 'Suemono' or 'Sueutsuwamono' during Heian period but it is unknown that it goes back to the Kofun period. In order to avoid confusion with 陶器 which is read "Toki" meaning earthenware nowadays, the archaeological term "Sueki" is commonly used. Sueki was sometimes called "Iwaibedoki," which meant celebration earthenware, until the former half of the 20th century.

Sueki originated in Korean Peninsula (especially in Kaya which was in the south of the peninsula), and early Sueki looks so similar to the one created in the peninsula that it is hard to distinguish between the two. However, the term "Sueki" refers to only hard earthenware created in Japan and fired in an oxygen-reduction atmosphere. The earthenware created in Korean Peninsula goes by just "earthenware" as a common name or by slightly more subdivided names such as Kaya ware, Silla ware and Baekje ware.

Whereas the ancient pottery including Haji pottery was made with clear characteristics of stacking up ring-shaped clays which was unique to Japanese archipelago, Sueki was made using the potter's wheel which was a completely different technique. Earthenware before Sueki was made having been fired on the ground uncovered. Therefore, the firing temperature was as low as 800 to 900 degrees C and the earthenware was not very hard. In addition, since it was fired in an oxygen-rich atmosphere, it was reddish in color on the surface. On the contrary, Sueki was fired in Anagama kiln (a Japanese pottery kiln that utilizes wood ash to glaze pottery) at high temperatures of more than 1,100 degrees C in an oxygen-reduction atmosphere. Although the oxygen supply runs short in a closed Anagama kiln, the firing proceeds by high temperature. If the oxygen supply is enough, the fuel turns into carbon dioxide and water, but the fuel turns into carbon monoxide and hydrogen in an oxygen-reduction atmosphere. These deprive oxide in the clay of oxygen, which is reduction, and turn into carbon dioxide and water. The characteristic color emerges when red ferric oxide in the clay changes into ferrous oxide through reduction.

Kofun period

The technique to produce earthenware with high temperature originated in Jiangnan area of China and was conveyed to Korean Peninsula. In the Nihonshoki (Chronicles of Japan), it is written that Sueki was made by toraijin (settlers) and in the meantime, it is also written that the Sueki craftsman visited Japan as a follower of the Prince of Silla Amenohiboko around the first century B.C. during the reign of Emperor Suinin. For that reason, the possibility that Silla-group Sueki (or earthenware) was spread cannot be denied. However, at present, early Sueki was not found at Kagamiyama ruins of old kilns in Ryuocho, Shiga Prefecture, which is closely-linked to this description, or either in Tajima region where Amenohiboko is said to have lived. Consequently, this technique is considered to have been conveyed from Baekje to Japan via Kaya.

In the archaeological point of view, it is believed that people started to produce Sueki in the middle of the Kofun period, which is around mid-fifth century. The oldest kiln in Japan is Obadera ruins of kiln in Sakai City, Osaka Prefecture. Suemura ruins of kilns spread in the foothills extending through southern area of Sakai City, Izumi City, Osaka-sayama City and Kishiwada City, and ruins of kilns at Koguma, Yamaguma and Yatsunami in Fukuoka Prefecture are known as places where Sueki production started first. Other early kilns were built all over Japan such as Suita 32nd kiln in Suita City, Okugatani kiln in Okayama Prefecture, Miyayama 1st kiln and Mitani-Saburo-Ike Seigan (west bank) kiln in Kagawa Prefecture and Yamaguma kiln in Yasumachi, Fukuoka Prefecture. Pottery made in these kilns belong to Kaya ware group.

Among these ruins of kilns, Suemura ruins of kilns in Osaka Prefecture is the largest in Japan and is located close to Mozu burial mounds which is considered to have the Imperial mausoleum. Suemura ruins of kilns are believed to have been controlled to produce the same standard of earthenware under Yamato sovereignty. Such 'quality control' can be seen at Fukada Remains and Kokanda Remains in Sakai City.

In the sixth century, kilns for Sueki were made in various locations in Japan. Suemura-type Sueki was produced in these Sueki kilns. By this fact, one theory holds that craftsmen to make Suemura-type Sueki spread out to local areas, whereas the other theory holds that craftsmen in local areas learned how to make Suemura-type Sueki and produced them. Although there are slight regional differences, it is certain that the nationwide-scale standardization was implemented. Thus, it is considered that Yamato sovereignty was playing the major role in Sueki production.

During the Kofun period, Sueki was used mainly for a religious service or as burial accessories. Early Sueki is unearthed only from tumuli, but later one can also be found in the remains of a village of western Japan since it was widely used. The difference emerged that Sueki was dominant in western Japan and Haji ware was dominant in eastern Japan.

Nara Period

After the Nara period, people started to make kilns for Sueki along with kilns to make roof tiles of kokubunji (a status of the state-supported provincial temples) in various places. Sueki was used basically at the government office of a state or a county, but started to be used daily as serving dish as well. Minamihiki ruins of kilns that are distributed around Hatoyama-machi of Saitama Prefecture represent those kilns. Production of Sueki reached Tohoku area along with building of an official defense site to confront Ezo (northerners).

Heian Period

In the Heian period, the system changed from "one county one kiln" to "one country one kiln" in western Japan where Sueki production was active, which led decrease in production areas. Behind this trend was the fact that a role of a county diminished on local governance and a country started to have a greater role. However, in eastern Japan, which was a remote region, production areas tended to spread on the contrary and new kilns increased in Kanto region. Although Sueki was not produced very much in the middle and the south of Tohoku region in the Nara period, people started to produce it actively in the ninth century. However, Sueki production declined at the end of the ninth century and ended in the tenth century replaced by earthenware that belongs to Haji ware group.

The farthest place of the expansion of Sueki production can be seen at Goshogawara kiln in Tsugaru Plain which was in operation from the end of the ninth century to the tenth century. Since Goshogawara kiln was at the outer edge or the outside of the territory dominated by Japan, Sueki products were sent not only to local Tsugaru Peninsula but also to Hokkaido.