Traditional manual clay preparation

Currently, in many domestic kyusu production areas, there is a rapid decline in kyusu potters who search for or make their own clay.

In fact, many kyusu potters obtain clay from suppliers or pottery associations. In other words, there are specialized clay suppliers from whom they procure finished clay.

The clay used domestically, regardless of the production area, is often a mix of several types of clay. As raw materials for the mix, Shigaraki and Seto clay, as well as recently Chinese clay, are commonly used.

Additionally, in traditional red clay production areas like Sado and Tokoname, it is not uncommon to add iron oxide, known as bengara, to achieve a redder color. While bengara itself poses no health concerns, the low melting point of iron oxide (600-800℃) means that when fired at the typical kyusu temperature of 1100-1200℃, the iron melts completely, becoming liquid like sugar in a frying pan. This results in the clay losing its porosity and not contributing to the flavor of the tea. It is quite common to find red kyusu that do not enhance the flavor of tea at all.

Tozo Watanabe obtains natural clay from the mountains and refines it into clay by hand. As far as I know, it is extremely rare for a kyusu potter to be involved in clay making from scratch.

Raw clay unearthed from the mountains contains various impurities such as tree roots and gravel. Removing these impurities and aligning the clay particles to make it usable as clay requires a great deal of time and effort.

Incidentally, even when using the same clay, different refining methods can change the properties of the clay and alter the taste of the tea brewed in it. This is due to the interaction with minerals like gravel included as impurities.

The following video summarizes the method of refining natural clay: