The “Heart” of pottery is the clay.

Choosing and preparing the clay, along with the skill of molding the piece and firing it in the kiln, is an extremely important element affecting the pottery landscape.The conditions that make clay suitable for pottery are its malleability and ability to maintain its shape when dried and fired in the extreme heat of a kiln. Historically, areas where clay meeting these criteria was extracted developed into pottery centers.

Shigaraki is one of the regions where high-quality clay is extracted.

It belongs to the distribution of the Hiroshima type granite and clay taken from this region is said to be the most suitable for pottery. The clay at Shigaraki is divided into “Gairome” or frog’s eye clay and “Kibushi” clay. The distinctive characteristics of frog’s eye clay are its content of granular feldspar and silica. It has a rough texture and sticky quality. The Kibushi clay contains deposits of trees that died, collapsed and were buried near rivers that flowed into ancient lakes. This is said to be the best original soil. It gives this clay resilience and malleability. Both types of clay are extracted from the ancient Lake Biwa stratum that dates from 430,000 to 4,000,000 years ago.

According to Mr. Hashimoto of the Shigaraki Pottery Manufacturers’ Co-operative Association, the clay contains a combination of four elements, namely, the frog’s eye clay and Kibushi clay as well as “Mizuchi” clay that is sticky and suitable for shaping, and the glass type silica that binds the original clay together. When it is difficult to guarantee the quality of the clay using exclusively local clay, about 30% of clay from other locations such as red clay is added.

At the Shigaraki Pottery Manufacturers’ Co-operative Association clay factory alone more than 40 types of blends are made and in the private sector clay manufacturers are said to produce nearly 200 types of clay.

Compared to other locations, the high content of granular feldspar and silica gives the finished product a rough texture. By preserving the texture of the soil and not using glaze, the pottery exudes a reddish “fired” or “scarlet” hue. Also, by firing it at a high temperature, the feldspar in the clay forms a white granular texture called “ishihaze”. During the firing process characteristics such as ash flecks on the surface and a natural glazing look are created by melting in the kiln. These natural processes of fire and clay beyond man’s control is a unique characteristic of Shigaraki. It is the high-quality of the clay, that gives birth to Shigaraki’s unique and warm human touch.

The soil of Shigaraki dates back approximately 65 million years. Magma flowed under the earth’s surface and hardened forming the granite that spread and became the foundation of Shigaraki’s clay. In addition, one other thing that cannot be overlooked when talking about Shigaraki’s clay is “Ancient Lake Biwa”

The geological stratum that stretches for 50 kilometers north and south from the shore of Lake Biwa to Iga City in Mie Prefecture is called “Ancient Lake Biwa”. It is the origin of modern-day Lake Biwa and was located near Iga City in Mie Prefecture about 4 million years ago. 400,000 years ago, it moved to its current location. The north part of the lake spread east and became the size it is today. At the bottom of Lake Biwa there is 250 meters of mud that has left us with a record of the environment for the past 400,000 years.

The ancient Lake Biwa layer group contains mud and swamp deposits in addition to lake deposits. The soil was transformed into the perfect clay for pottery thanks to the granite and decayed matter that flowed into ancient Lake Biwa stratum which was formed by sediment, and the deposits of animal and plant remains. This is why the high-quality clay of Shigaraki that has been described as “miraculous clay” formed over the ages.