Shirogeshou: How Japanese Potters Make Dark Clay White

Shirogeshou is the decorating technique of coating a clay body that fires red or grey with a white liquid clay — white slip, also called engobe — so that the piece reads as white. The Japanese word uses the characters for "make-up": the slip is powdered onto the pot much as white powder is applied to skin, covering the colour of the clay underneath.

Unlike Japanese porcelain, the clay itself is not white. A second, white layer sits on top of a coloured one. Everything that defines white slip pottery comes from that doubling — the softness of the white, the red-brown that shows at the rim, and the way the surface changes the more the piece is used.

The best-known form of white slip is Kohiki (white slip ware), and the version that keeps the marks of the brush is Hakeme. Both are members of the larger shirogeshou family.

Why Potters Wanted to Make Clay White

For most of ceramic history, white was a colour that was not easy to come by.

A truly white pot requires white porcelain stone with almost no iron in it. Chinese Japanese Stoneware and Porcelain Explained had access to exactly that. But in Korea and across most kiln regions in Japan, what could be dug from the ground nearby was iron-rich clay that fired red-brown or grey.

What emerged was a simple piece of reasoning: if you cannot obtain white clay, paint white clay on instead. On the Korean peninsula the technique flowered in the 15th and 16th centuries as buncheong ware, and from there it travelled to Japan and took root in the western kilns, Karatsu above all.

Shirogeshou, in other words, is a technique born out of making up for something that was missing. In Japan, though, it was the evidence of that making-up — the unevenness of the brush, the ground colour peeking out at the rim, the boundary between white and red-brown — that came to be seen as beautiful, and it was valued on entirely different terms from porcelain. The sensibility identified in Mingei and the Beauty of Use: Japanese Pottery’s Mind lies along the same line.

How White Slip Is Applied

Slip is white clay let down with water to the consistency of cream. It is applied while the formed pot is still leather-hard — half dry, with the firmness of leather.

Apply it to a fully dried body and the slip shrinks first and flakes away. Apply it when the clay is too wet and the pot itself collapses. There is only a short, narrow window in which it can be done at all, and that is what makes white slip difficult.

From there, the sequence usually runs like this.

• 1. Forming　The shape is made, often by Rokuro seikei (wheel throwing)
• 2. Slipping　White slip is applied while the piece is leather-hard (dipped, poured, or brushed on)
• 3. Drying and Suyaki(bisque firing)　A low firing at around 800°C fixes the slip to the clay body
• 4. Glazing　Usually a clear glaze. A colourless glaze is chosen so as not to kill the white underneath
• 5. Final firing　Fired to maturity at 1,200–1,300°C

Seen in cross-section, the finished piece has three layers: clay body, slip, clear glaze. That structure is the real reason these pieces "grow," as described further down.

Five Faces of White Slip

The same white slip gives a completely different face depending on how it goes on. Here are the main ones.

White slip also serves directly as a ground for Shita-etsuke (underglaze decoration). On red clay a painted line sinks and disappears; interpose a single white layer and iron pigment or cobalt rises clearly to the surface. Many of the techniques covered in Japanese Pottery Patterns Guide: Traditional Motifs, Eitsuke Techniques only work because a white ground is there first.

White Slip, White Glaze and Porcelain: What Is the Difference

There are three kinds of "white" in Japanese pottery, each arrived at differently. Once you can tell them apart, you look at pieces in a shop differently.

Why White Slip Pottery "Grows"

What people love most about these pieces is not the whiteness itself but the fact that the white changes.

The reason is structural. The clear glaze on the surface develops fine cracks as it shrinks after firing — crazing. The slip layer beneath it is less dense than glaze, and it takes in moisture. Which means:

• Tea and sake seep in through the gaps in the crazing
• The stain spreads into the slip layer and the white shifts slowly towards a natural, unbleached tone
• Because it soaks in unevenly, cloudy patches appear — a look called amamori, "rain leak"

On the day you buy it, white slip is a cool, even white. Six months of use settles it a little; after a few years, veins of crazing appear like the ribs of a leaf, along with a soft greyish white. What you have drunk and eaten from that piece stays on the surface, exactly as it happened.

In Japan this is described as the piece "growing." It is received not as dirt but as a record of time. For more, see Japanese Ceramics That Grow: How Handmade Pottery Changes and Deepens with Every Use and Keinen bika (beauty through aging).

Making White Slip Pottery Last

Absorbency means the handling takes a little know-how. It is not difficult.

• Season it with Medome(Sealing,Seasoning) before first use.　Simmer it gently for 20–30 minutes in the cloudy water left from rinsing rice. The starch fills the crazing and makes odours and stains far less likely to take hold
• Wet it before you use it.　Pour soy sauce or coffee straight into a dry piece and only that colour goes in strongly. Letting it drink water first means it grows evenly
• Dry it completely after washing.　Put it away damp and mould develops in the slip layer as black spots. Leaving it upside down overnight is the reliable method
• Avoid the dishwasher, the microwave and bleach.　High heat and sudden wet-dry swings put the most strain on the boundary between slip and glaze

General handling is covered in Japanese Ceramics Care Guide.

Kiln Regions Known for White Slip

• Karatsu　Kohiki Karatsu, hakeme Karatsu, mishima Karatsu. This is where white slip began in Japan.
• Mashiko　Thick white slip combined with sgraffito carving, in the lineage of the mingei movement.
• Kasama　A wide range of individual interpretations, with a great deal of contemporary work in white slip.
• Onta and Koishiwara　Tobikanna chattering and hakeme brushwork. Known for cutting patterns back through the white slip.

Related Articles

Techniques in the White Slip Family

• Kohiki (white slip ware)
• Hakeme
• Icchin (trailed slip decoration)
• Japanese Pottery Decorating Techniques

How Japanese Pottery Is Made, and What It Is Made Of

• How Japanese Pottery Takes Shape
• Japanese Pottery Glazes: An Introduction
• Japanese Stoneware and Porcelain Explained

Growing and Using Japanese Ceramics

• Japanese Ceramics That Grow: How Handmade Pottery Changes and Deepens with Every Use
• Crazing in Japanese Pottery: The Beauty That Deepens with Every Use
• Japanese Ceramics Care Guide