【Japanese Pottery】What is Underglaze and Overglaze (下絵と上絵)? With image-based explanations.

Table of Contents

• 1. Underglaze and Overglaze Decoration (下絵付と上絵付)
• 2. Yūkasai and Yūjōsai (釉下彩と釉上彩)

1. Underglaze and Overglaze Decoration (下絵付と上絵付)

Underglaze (下絵, shita-e) refers to painting a design beneath the glaze and then firing it at a high temperature. In the example below, a blue design has been drawn using gosu (呉須, a cobalt pigment). When viewing the vessel, you’ll notice a composition of white clay body, blue underglaze design, and red and gold overglaze decorations.

In practice, a bisque-fired vessel (fired at around 600°C to 800°C) is painted with gosu, then coated with a transparent glaze and fired again at a high temperature (1,200°C to 1,300°C). Since gosu contains cobalt oxide, it can withstand high-temperature firing without any issue.

View the products used in this image.

What is Overglaze (上絵, uwa-e)?

In contrast, overglaze decoration refers to painting on top of the glazed surface and firing it at a low temperature. After the main high-temperature firing, the vessel appears complete with its white body and blue underglaze. On this surface, red pigments and gold (金彩, kin-sai) are applied, and then the piece is fired again at a lower temperature of around 600°C to 800°C, similar to the initial bisque firing.

Why is low-temperature firing necessary? It’s because gold and other colored overglaze pigments may melt or become unstable under high temperatures.

For reference:
・The melting point of pure gold is 1,064°C
・The melting point of iron oxide (commonly found in red pigment) is 1,566°C

However, when blended with other materials to make pigments, these melting points can be significantly lowered. Therefore, overglaze decorations are fired at lower temperatures to prevent the pigments from liquefying.

Gold and color-decorated ceramics are often labeled as unsuitable for microwave use because of their vulnerability to heat. Not only can the decorations be damaged, but the ceramic body itself may also suffer harm. For this reason, it is best to avoid using any valuable or decorated ceramic ware in microwaves.

Overglaze decoration began with sometsuke (染付, blue-and-white porcelain) in Arita. The following are known as the "Three Great Overglaze Porcelains" of early Japanese ceramics:
・Shoki Imari (初期伊万里, Early Imari)
・Ko-Kutani (古九谷, Old Kutani)
・Himezuyaki (姫谷焼, from present-day Fukuyama, Hiroshima)

These techniques have been passed down through generations and continue to influence ceramic arts throughout Japan today.

2. Yūkasai and Yūjōsai (釉下彩と釉上彩)

Previously, the term underglaze (下絵, shita-e) referred specifically to painted decorations. However, in a broader sense, decorations applied beneath the glaze are called yūkasai (釉下彩), while those applied on top of the glaze are referred to as yūjōsai (釉上彩).

Yūkasai (釉下彩: Under-Glaze Decoration)

This includes what is commonly known as underglaze painting (下絵付, shita-e-tsuke). Other techniques under this category include:
・Zōgan (象嵌): Inlaying differently colored clay into the base clay, then applying a transparent glaze and firing the piece
・Hakeme (刷毛目): Brushing a white slip (e.g., white-colored clay) onto a dark clay body before glazing and firing
・Yūriko (釉裏紅): Decorating with copper oxide, applying a transparent glaze, and then reduction-firing the piece, resulting in a red coloration

Yūjōsai (釉上彩: Over-Glaze Decoration)

This mainly refers to overglaze painting (上絵付, uwa-e-tsuke). In Japan, such decorations are generally referred to as aka-e (赤絵) or nishiki-de (錦手). In Chinese ceramics, they are known as:
・Wucai (五彩, literally "Five Colors")
・Fencai (粉彩, soft pastel-colored overglaze enamels)

These terms categorize decorative styles based on whether they are applied beneath or above the glaze, expanding beyond just brushwork to include various traditional techniques.