Mogake: The Red Seaweed Lines of Tokoname Pottery

Mogake is decoration made by wrapping dried seaweed around a formed piece and firing it, so that wherever the seaweed touched is left as a red line. It was born in Tokoname, Aichi Prefecture, and belongs to that pottery region alone.

It is not painted with a brush, and it is not made with glaze. The seaweed burns away in the kiln, but the salt it contains is said to react with the surface of the clay, turning only the places it touched red. Wherever the seaweed happened to lie becomes the pattern, so no two pieces are ever the same.

It is one of the keshiki that appear on the surface of pottery fired without glaze.

Salt from seaweed turns the clay red

The process itself is simple. Dried seaweed is wrapped around a piece that has been thrown on the wheel and left to dry. The piece goes into the kiln as it is. That is all.

What happens in the kiln is a reaction, not burning. The seaweed is consumed by the heat, but the salt it held is explained as staying only on the clay it touched, reacting there and turning that area red. Wrapped around a clay that fires white, such as white slip clay (hakudei), it leaves a crisp red line on a white ground. On pieces made from Tokoname's red clay, the line appears as a reddish-brown darker than the ground.

The character of the line comes from how the seaweed is wrapped. A single strand run vertically, many turns wound on the diagonal, or a bundle laid against the piece. Depending on the thickness of the seaweed and how it overlaps, the line runs fine or branches out like a net. Not even the maker knows how it will come out until the firing is done.

The Tenpō era, and a white clay

Tokoname Tounomori, the city's ceramics museum, and the official site of the Japan Heritage "Six Ancient Kilns of Japan" both place the beginnings of mogake in the late Edo period. In the Tenpō era (1830–1844), Ina Chōza II found a clay at Itayama that fires white — hakudei — and developed a technique of wrapping that clay in dried seaweed before firing, according to both.

The first name was hiiro-yaki, "fire-colour ware". The contrast between the white body and the red that the seaweed's salt brought out was the whole point of the technique. Tokoname Tounomori explains that the name "mogake" later spread, and "hiiro-yaki" fell out of use.

As for the seaweed itself, Tokoname Tounomori records it as koamamo (dwarf eelgrass, a kind of eelgrass). Other sources name amamo or juzumo instead, and it cannot be settled on a single species.

Mogake is still treated as one of the defining techniques of Tokoname ware. Aichi Prefecture's official page on Tokoname ware as a designated traditional craft lists "mogake-yaki" as one of the finishes used in making teapots.

How it differs from hidasuki

The technique most often confused with mogake is Bizen's hidasuki. Both work the same way in one respect — organic material is wrapped around the piece and fired, and what it contains turns the clay red — and in a photograph the two can be hard to tell apart.

What differs is the material wrapped, the clay beneath, and the region. And how each came about.

The easiest tell is the shape of the line. Rice straw is straight, stalk by stalk, so hidasuki lines cross as straight lines. Seaweed has a branching form, so mogake lines split finely and tangle together. Pick up the piece and follow a line with your eye, and you will know at once which technique it is.

They were born in opposite ways, too. Bizen City's official site explains hidasuki as coming from a kiln-packing practice: straw placed between pieces so they would not fuse together. Hidasuki is a practical fix that turned into a landscape; mogake was devised from the start to make a pattern.

The explanations of the colour also differ in how certain they are. The Bizen pottery cooperative explains hidasuki as a reaction between the alkali in the straw and the iron in the clay, and materials-science research has examined the red and identified it as iron oxide. For mogake, even the official sources stop at "caused by the salt in the seaweed", and no study confirming the mechanism can be found.

Where it sits beside yakishime and shizen-yu

Mogake is not itself the name of a glaze. It is one of the keshiki that appear on pottery fired without glaze. Tokoname is a region known for unglazed yakishime, and it is precisely because the clay is bare that what the seaweed contains can react with it directly. Similar words line up when a single piece is described, so it helps to sort them like this.

• Yakishime　The method of firing clay to a high temperature without glaze. Yakishime names how a piece is made
• Shizen-yu　Wood ash that settles on a piece and melts in the heat into glass. Shizen-yu is a glaze, so it gives the surface gloss and depth
• Mogake　Clay turned red by what was in the wrapped seaweed. It is not a glaze, so it adds neither gloss nor depth
• Keshiki　The word for all these expressions that appear on unglazed pieces. Keshiki is about how to read them

Run a finger over the surface and the difference is clear. Shizen-yu rises as a film of glass, but a mogake line is still the surface of the clay; only its colour has changed. Where shizen-yu is left to the kiln's chance, mogake puts the pattern where the seaweed was wrapped, which makes it a keshiki the maker can half guide. In the way the kiln's conditions move the colour, it shares something with yōhen.

Mogake from Tokoname

The mogake pieces at Nokaze are by Yamada Yutaro of Tokoname. Born in 1982 into a Tokoname pottery-making family, he studied in the ceramic arts course at Tokoname Prefectural High School, then architecture at Daido University, and completed the Tokoname Tounomori Ceramic Research Institute in 2017. Apart from the family business, he became independent as a maker of tea utensils.

Made with a traditional Tokoname technique, wrapped in mountain seaweed before firing to create a distinctive pattern, his pieces are marked by their lightness and thinness, and by the beauty of mogake.

• Yamada Yutaro

Tokoname is one of Japan's Six Ancient Kilns, a region that has fired ceramics without a break since the medieval period. The late Edo period, when mogake was born, was also when teapot making began in Tokoname alongside the fashion for sencha. Tokoname's way of finishing a piece with nothing but clay and fire runs through the Tokoname kyusu as well.

Choosing a mogake piece

Every mogake piece carries a different pattern, so once you have settled on the region and the maker, you choose by how the lines run. There are three things to look at.

• How many lines　A single line passing through reads as quiet; many tangled lines give the piece a stronger expression
• Where the lines fall　Down from the rim, across the body, or gathered at the shoulder. Check that there is a line on the face you see most when the piece is in your hand
• Contrast with the ground　On a white ground the red stands out clearly. On a vermilion or black ground it shows quietly, as a difference in depth

This is unglazed pottery, so the colour settles and a sheen comes up the more it is used. This change is called keinen bika, and the mogake lines, too, blend into the ground over the years. For first use and washing, follow the guidance from the maker who made the piece.

Related reading

Related terms

• Hidasuki: The Red Straw Marks on Bizen Pottery
• Yakishime: Unglazed Pottery Fired to Its Limit
• Shizen-yu: Natural Ash Glaze Explained
• Anagama: Inside Japan's Oldest Wood-Fired Kiln
• Keinen Bika: Pottery That Gets Better With Age
• Japanese Pottery Glossary

Learn more

• Keshiki: How to Read the 'Landscape' on a Pot
• Tokoname Kyusu: Why Red Clay Makes Tea Taste Better
• Japan's Six Ancient Kilns: All 6 Regions Compared
• Yunomi: How to Choose a Japanese Tea Cup
• Japanese Flower Vases

Pieces available at Nokaze

• Tokoname Ware | Japanese Kyusu Teapots in Red Shudei Clay