Polarizing microscope observations of pottery from the Yashiro sites, Nagano Prefecture, Central Japan

Inhabitants of the Japanese archipelago historically relied on pottery constructed from clay and sand and fired at approximately 700-900 °C using fuel. This pottery was used from the Jomon to Yayoi periods (13,000 BC-250 AD) despite large cultural change between them. The workmanship of pottery largely depends on the quality of the resources. This study identifies the pottery paste of locally-made pottery and researches the relationship between Jomon and Yayoi pottery. For this purpose, pottery excavated from the Yashiro sites, located in Chikuma City of Nagano Prefecture, which was intermittently produced from the Jomon period to medieval times, was sectioned for microscopy study. The 119 samples of pottery paste were observed under a polarizing microscope and materials were qualitatively classified according to type, size, and quantity of sand fragments (rocks and minerals). Five main categories of ancient pottery were identified. Locally-made pottery in the Jomon period was mainly derived from Susobana tuff material, approximately 5 km from the Yashiro sites. However, this pottery paste was replaced in the Yayoi period by epidote-rich groups. This result suggests that the technical tradition of Jomon potters ceased, and was replaced by new pottery during Yayoi period. The altered distances to pottery resources and the advent of new large village may signify that production zone also changed between the Jomon and Yayoi periods. The new pottery may have been produced in a specific village and become widely accepted. This paper presents the first proposition to the production systems of Jomon and Yayoi pottery by examining the petrology of excavated samples at sites intermittently occupied by humans during the last 4,300 years.