Fumiya Mukoyama's Zogan Yusai: Precise Pottery Decoration with Slip Inlay and Glaze Patterning Naomi Tsukamoto

For a young potter in a region of Japan where Mingei is king, coming up with a unique style can be challenging. But Fumiya Mukoyama did just that with his "Zogan Yusai" technique. Translated, "zogan" means inlaid and "yusai" means coloring with glazes. And as the name implies, Fumiya's technique consists of slip inlay and colored glazed designs.

Today, Naomi Tsukamoto shares Fumiya's technique step by step. In addition to the fabulous pottery decorating methods, I particularly liked Fuyima's method for trimming on a chuck. - Jennifer Poellot Harnetty, editor

Throwing & Trimming

Mukoyama uses several different tools and techniques to create multiple pieces of the same size, and to create a clean surface for his designs.

He throws the tea bowls off the hump, starting with a large lump of clay, centering it into a wide cone, then shaping, centering, opening, and throwing an appropriate-sized portion of the top section of this cone. As Mukoyama throws, he uses the curve on the wooden rib to determine the inside shape of the bowl.

Tip: When throwing off the hump, be sure to thoroughly compress the bottom interior of your vessel to prevent S cracks.

The tombo is a depth and diameter gauge. The one shown here (figure 1) consists of two pieces of wood joined perpendicularly, with a thin bamboo dowel cut to exactly the desired diameter of the bow that slides through a hole in he lower piece of wood. The piece inserted into the bowl is exactly the right height so that it touches the bottom of the bowl when the dowel marking the proper diameter rests on the rim of the bowl. Once you decide on a height, and cut the thin dowel to the desire diameter, you can create many pots of the same size.

After you finish throwing, cut the pot off the hump. Be careful to mark a line first so you don’t cut through the bottom. After the piece is leather hard, you’re ready to trim.

When trimming, use a chuck to keep the form well supported, prevent it from warping, and elevate it from the wheel head so that it can be trimmed all the way to the rim. If you don’t have a chuck already, throw a somewhat mushroom shaped solid form with a slight concavity and beveled top edges on a bat or on your wheel head like the one shown here (figure 2) and leave it attached. Once it is leather hard, it is ready to use.

Before trimming, use a surface gauge to determine the height of the foot (figure 3). This is especially necessary when throwing off the hump as the cuts made when removing each piece from the wheel may not result in a bottom with the same thickness each time.

Once the foot is trimmed to the proper height, the U-shaped gauge is used to determine the width of the foot (figure 4). The foot is then trimmed to this diameter. The next step is to trim the piece from the bottom all the way to the lip of the bowl. This removes excess clay and throwing lines and creates a smooth surface. In order for the inlaid design to come out clearly, it is important to make the surface as smooth as possible at this stage. Mukoyama ends the trimming by going over the surface with a sponge, erasing all the trimming lines. Finer clay works better for the zogan technique, and so a sponge works well. A rubber or metal rib would work if you are using coarser clay.

Drafting and Etching the Design

In order to determine where the circular patterns will be placed, Mukoyama draws drafting lines with calligraphy ink, dividing the surface into six sections (figure 5).The tools used to create geometric shapes do not have to be fancy. Here a medicine bottle cap is used for the circular pattern (figure 6). The lines on the cap help him to line up the circle vertically and horizontally with the lines drawn on his pot.

Clean and round the edges with a trimming tool after etching the design. After smoothing them, go over the lines with the needle tool to round inside of the lines.

A fabric rotary cutter (or a pizza cutter) is used to etch the dotted lines within the circles (figure 7).

Zogan (Slip Inlay)

Because the slip is only inlaid inside the lines, Mukoyama uses watered down pure Amakusa Porcelain Stone powder, which is equivalent to Cornwall Stone. This simplifies cleaning the surface later. This slip will not work for painting the surface though, because once dried, it is powdery and will flake off easily.

The slip should be quite watery, much thinner than the normal consistency, in order to fill in the small dots. Use the brush to lightly pat in the slip (figure 8). Once the slip dries, and becomes powdery, rub in the slip further using your fingertips (figure 9).

Normally, you would scrape the surface in order to finish the slip inlay; however, since the slip was pure clay, all you need to do is to wipe off the surface lightly with a cheese cloth like fabric (figure 10). Be cautious not to wipe the surface too hard, otherwise, you will lose the inlaid lines. The more clearly you can maintain the division between the inlay and surrounding surface, the more vivid the final colors will be. After cleaning the surface, bisque fire the piece.

Glazing the Background

Once bisque fired, make sure you clean the ware with a wet sponge first in order to achieve the best glazing result. Brush wax resist on the circular patterns. Mukoyama usually covers the lines with water-based latex resist using a very thin brush first, and then fills inside the design with melted wax mixed with kerosene using a small brush. Using latex on the lines ensures that the resist can be removed and reapplied if it is covering more than just the incised lines and patterned areas.

After the resist dries, glaze the inside by pouring first, then dip the base glaze outside. Wipe any glaze off of the circular design areas and clean any drips on the foot ring before the second bisque firing. The purpose of the second bisque firing is to burn off the resist and to fire on the base glaze.

Yusai (Coloring Designs with Multiple Glazes)

After the second bisque, only mask off the lines (figure 11). You will want to fill in the rest of the area using colorants and glazes. Because some glazes do run, it works better if you mask a little over the lines rather than precisely covering only the lines.

Fill in each pattern with different glazes, metallic oxides, and/or underglazes. Mukoyama only uses two colors for each pattern to achieve a unified balance (figure 12).

You could also leave some parts bare to take advantage of the clay color. Glaze from lighter to darker colors as you work to keep them from contaminating one another.

This is the last glazing step. Think of glazes and stains as colors and carefully consider the color balance for each circular pattern and between the patterns. Also consider the type of finish (glossy, matte, and dry) you combine. Depending on how you combine the linear patterns and colors, you will find numerous design possibilities in zogan yusai.

Naomi Tsukamoto received her MFA from the University of Colorado, Boulder. She currently teaches in Tokyo and works from her studio in Yokohama, Japan.

Fumiya Mukoyama graduated from Kyoto Prefectural Ceramics Training School in 1984, then studied under Shinbei Sakakura in Hagi. He now lives in Karasuyama-cho in the Mashiko region with his family.