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Table of Contents
1.　What is Glaze?
2.　Main Types of Glazes
＿2-1. Classification by Constituent
＿2-2. Classification Based on Differences in Texture
＿2-3. Classification by Color
3.　How to Apply Glaze
4.　Natural Glaze
5.　Conclusion

What is Glaze?

Glaze is a liquid made by mixing mainly ash or clay and dissolving it in water. By applying this to ceramics and firing it in a kiln, the ash melts due to the temperature and flame of the kiln, becoming glassy and coating the surface of the ceramics.

Coating the surface prevents water from seeping into the vessel and increases the strength of the vessel. It is also used for decorative purposes, as its color and texture change depending on the type of raw material and baking method.

Main Types of Glaze

Glazes are classified in different ways.

Classification by Constituent

■Ash glaze (Kai yuu)
A high-temperature glaze that is made from wood ash, earth ash, straw ash, etc. and melts at temperatures above 1250℃. In Japan, it was developed in the Sanage kiln during the Heian period. Milky white or clear color.

■Feldspathic glaze
Mainly feldspar is used, mixed with earth ash and straw ash. A high-temperature glaze that melts at over 1100℃. It is characterized by its soft milky white color and the pattern of cracks that appear on its surface.

■Lead glaze
A low-temperature glaze made from lead oxide that melts at 800℃. It is sometimes used as a coloring material for colored paintings and overglaze paintings.

■Iron glaze
The raw material is iron, and the color changes depending on its content and firing conditions. A trace amount of iron will result in a yellow or celadon glaze, while around 10% will result in a black or persimmon glaze.

■Copper glaze
The raw material is copper, and the color changes depending on its content and firing conditions. Typical examples are green glaze and cinnabar glaze.

Classification Based on Differences in Texture

■Transparent glaze
Most of the glaze melts during firing and becomes transparent. The feature is that you can make the most of the transparent color of the base material.

■Matt glaze
The undissolved components of the glaze crystallize. Leaves an opaque, non-shine finish. If you use it as tableware, you need to be careful as it may be difficult to remove stains or the dirty parts may discolor easily.

Classification by Color

Even if the same glaze is used, the finished color will differ depending on whether it is oxidized or reduced fired.

*Oxidation firing: A chemical reaction that occurs when the fuel in the kiln is fired with enough oxygen to completely burn, and the metal components of the clay and glaze combine with oxygen.

*Reduction firing: Firing in which the amount of air in the kiln is restricted to create incomplete combustion and suffocation, using a flame containing carbon. A chemical reaction in which carbon monoxide in the kiln removes oxygen from the hammer and glaze.

■Green glaze
It often refers to a copper green glaze made using copper oxide. High-temperature glazes (those that melt at temperatures above 1100℃) were used as Oribe glazes, and low-temperature glazes (those that melted at around 800℃) were used for ancient Sansai and green glazes.

■Yellow glaze
A trace amount of iron develops a pale yellow color due to oxidation firing. Kiseto glaze is typical.

■Black glaze
It develops a black color due to large amounts of iron. Typical examples include Setoguro and Tenmoku glazes. It is often used as a tea bowl.

■White glaze
A white base made of gairome clay mixed with silica stone and silica sand, coated with a transparent glaze. Or, the glaze becomes milky and white color. In Japan, it began to be made in Imari in the 17th century.

■Cinnabar glaze
Black copper oxide is added to the transparent basic glaze, and the color develops into a blood red color through reduction firing.

■Persimmon glaze
When the iron content is reduced and fired, it becomes brownish-brown, and when it is oxidized and reduced, it becomes blackish. It is baked in places such as Mashiko, Japan.

■Celadon glaze
The iron content develops a bluish-green color through reduction firing. Goryeo celadon from Korea is famous. In Japan, it spread around Arita.

■Lapis glaze
Bright blue, indigo, and lapis lazuli. It is made by adding cobalt oxide to feldspar glaze. Lazuli glaze has been used in Arita since the early Imari period.

How to Apply Glaze

There are various ways to apply glaze. Even if the glaze is the same, the impression of the pottery will change depending on how it is applied.

・Soaking: Dipping the pottery directly into the glaze. Can be glazed evenly, but requires a lot of glaze. Even beginners have fewer mistakes.
・Naguri: Apply glaze using a ladle.
・Spraying: Spray with a spray, etc. It is possible to adjust the darkness.
・Painting: Apply using a brush, etc. Easy to paint unevenly.

Natural Glaze

The oldest glaze method is natural glaze. Natural glaze refers to the fact that the ash in the kiln falls naturally during firing, which melts and naturally forms a glassy substance, rather than applying glaze and firing as we have introduced above. The color and texture vary depending on the type and size of the kiln, firing method, and other conditions.

Conclusion

Glaze has made it easier for people to handle ceramics in their daily lives by coating the surface to prevent stains and make them less likely to break.

The glaze also greatly affects the impression and finish of the pottery. Even if you use the same material and the same glaze, you can end up with a different finish depending on the conditions of the kiln and flame at the time. One of the things that fascinates artists is that it is impossible to create exactly the same thing, and that it is a product of chance.

If you pay attention to the glaze when purchasing or making your own ceramics, you may be able to enjoy them from a different perspective than before.

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