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Nosaka teapot
The colour and texture of the teapot varies a lot, where the same clay could turn red, purple or black based on just the firing technique. In addition, the use of different firing techniques not only changes the colour of clay, but also the taste and flavour of the tea when it is brewed. Therefore, when selecting a teapot, it is important to consider the effects it brings to a tea rather than the colour of the teapot.

Oxidation and Reduction Firing

Mainly, there are 2 different firing techniques, which are oxidation and reduction firing. Oxidation firing is a process where complete and perfect combustion occurs when sufficient oxygen is supplied, converting all the fuel into carbon dioxide (CO2) and water (H2O). However, in reduction firing (also called incomplete combustion), the oxygen supply is insufficient for a complete combustion. However, hydrogen is still oxidized to water, but carbon monoxide is formed instead of carbon dioxide. Solid particles (particulates) are also released which contains carbon (C) and are seen as soot or smoke.

The oxidation fire exhibits blue flames while the reduction fire exhibits orange flames.

Allow me to illustrate more about the flame that both oxidation and reduction firing produces. For instance, let’s take our home cooking gas stove as an example, and lid it up; blue flames will ignite out from the burner. Thus, this flame is called the oxidation flame (sufficient oxygen supply). On the contrary, a reduction flame (insufficient oxygen supply) is the fire on a candle or an open fire which is of orange to red color.

3 types of hohin

The houhin on the left is a Mumyoi reduction clay, the center is a Tokoname oxidation clay and the one on the right is a Mumyoi oxidation clay.

The oxidation fire oxidizes the minerals

The oxidation fire oxidizes the clay as it releases a lot of heated oxygen during combustion. With oxidation fire, the minerals in a teapot are oxidized. For instance, iron is a mineral contained in clay and when a clay is rich in iron, after heated, it gets oxidized (oxidation of iron) and turns red. Another common exemplar, when a cast iron kettle or a frying pan is heated on a gas stove, the bottom part tends to turn reddish in color. This is also due to the oxidation of iron.

Nosaka oxidation clay by Watanabe Tozo

The reduction fire reduces minerals

On the contrary, a reduction fire releases carbon monoxide (CO) and hydrogen gas (H) as the by-products. These molecules are unstable and therefore looking for other free atoms like oxygen (O) to bind with and achieve stability. Thus, the availability of oxygen in the clay allows binding of molecules to occur, producing an end-product of carbon dioxide (CO2) and water (H2O). Hence, when a clay that is rich in iron, it may appears in different colours ranging from blue to black as a result of reduction [Fe2O3 + CO ===> 2FeO + CO2 (FeO, ferrous iron oxide)]. This is the mechanism minerals get reduced during combustion.

The firing methods of clay affect the taste of tea

The different firing methods not only affect the color of the clay, but also the taste and flavor of a tea. For my up-coming lineups of clays, such as Mumyoi, Nosaka and the new Kobiwako clay, I have produced them both with oxidation and reduction fire. They are all very colorful and beautiful. But, I strongly suggest that you choose a teapot deliberately not just based on its color, but the effect it brings to the tea. Allow me to share the basic conception in taste based on oxidation and reduction fire.

Kobiwako clay

Body

Oxidation Fire > Reduction Fire

After Taste

Reduction Fire > Oxidation Fire

Do you prefer body or after taste?

The above idea in taste is applicable for most kinds of clay. For example, the Banko teapot is a typical reduction fired teapot. It produces less body than the tea brewed in a glass teapot, but increases the after taste of the tea. With a lighter body, the flavor also becomes lighter. Since it is of this character, a reduction fired teapot is usually suitable to brew Green tea and ripe Pu-erh tea. However, for fermented teas such as an oolong or black tea, oxidation fired clay is generally more suitable as it gives more body. As a result, the flavor would spread wider in our mouth. Nonetheless, it is pretty subjective on whether one would appreciate more after taste or body. I have noticed many cases where my customers would select a reduction clay as they would prefer nothing but a strong after taste even if it sacrifices the body. After all, it is based on one’s preference to use an oxidation or reduction clay. In any case, it is essential to understand the property and conception in taste.

Two different reduction fired clays

There are two different types of reduction firing techniques commonly used by teapot artists in Japan. The first one is using reduction fire throughout the firing process, while the second method starts with oxidation firing and subsequently re-fires with reduction fire. For instance, Banko teapot is fired with reduction fire throughout the firing process, whereas the reduction Nosaka and Mumyoi clay wares are fired using the second method. Because of the two-steps firing method, the inner part of the clay will be red in color even if the teapot looks black. Based on my experiment, the effect to the taste of tea is more or less the same between both the firing methods.

Banko Teapot

Banko Teapot by Masaki Tachi

shigaraki teapot by masaki tachi

Shigaraki clay teapot by Masaki Tachi. Although this teapot looks beige in color, it has undergone reduction firing. For some clays, it is hard to judge based on the color whether it is reduction or oxidation

Body and After Taste

After taste means softness, smoothness, long lasting, clarity, lingering feeling.
Body means heaviness, weight, width, richness.

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