The sintering process of a broken piece of Bizen-yaki vase discovered in Mizunoko-iwa and its components were studied by means of X-ray diffraction and electron microscopy. The components of the sample discovered in Mizunoko-iwa were mainly mullite, cristobalite, quartz and feldspar. Quartz and feldspar were much contained in it, compared with Bizen-yaki of recent days. It is considered that the sintering process was similar to the process now in current. As a result of electron microscopy, the needle-shaped and thin crystal were observed in the sample above mentioned. The formation of needle-shaped crystal was considered to be due to the reaction with the sea water. The Bizen-yaki vases in Mizunoko-iwa were generally porous and raw materials were comparatively rough
