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Ash Glaze

Ash glazes are high fire ceramic glazes containing wood-ash that have been used for centuries. Ash glazing was first discovered in China by accident when hot ash melted on the pottery pieces. Then it evolved to its present state as a decorative tool and a coating for dish-ware. Typically glaze making is a science with its components measured carefully, but with ash glaze, the ash contains an unknown amount of its chemical components.

A Yunomi or tea cup with an ash glaze made from pine ash.

Appearance

The glaze has glasslike and pooling (the builds up of glaze) characteristics which puts emphasis on the texture of the piece. When the glaze is mostly made up of ash, the final result is mostly dark brown to green. The pots with these glazes resemble the earth in color and texture. As the ash percentage decreases, the artist has more control on the color and the final glaze color differs from light to dark shades of brown or green.

History

Ash glazing began around 1500 BC, during the Shang Dynasty, in China. It occurred accidentally when hot ash from the wood fueled kilns landed on the pots and the ash melted into a glaze. Around 1000 BC, the Chinese realized that the ash was covering the piece so they started adding the ash as a glaze before the pot went into the kiln (an oven-like structure used to turn the ceramic piece into its usable form). Ash glaze was one of the first glazes used and contained only ash, clay, and water.

Present Glaze

Current ash glazes usually contain less than 50% wood ash compared to before when the majority of the glaze was ash. The decrease in ash percentage is to give the artist some control over the chemical make up and result of the glaze. Currently, ash glazes are mostly used by artists as a decorative tool, but some still use ash glaze dish-ware. In Korea, the traditional ash glaze composed of only ash and water is used to make functional pottery such as bowls, cups, and teapots. Koreans believe using ash glazed ceramic dish-ware is dramatically safer than using plastic ware because of its lack of carcinogens, cancer causing materials. The firing process to turn the glaze into glass gets rid of all the impurities in the ash and clay, making it food safe.

Making the Ash

To create the ash, the wood needs to burn completely in a kiln. Wood-ash is around 1% the mass of the original wood; therefore, a lot of wood is necessary to produce the ash. The ash is then put through a sieve, a meshed tool, to eliminate the excess clumps from the ash. At this point artists can process the ash further to create a more uniform mixture or leave it unprocessed so there are more random final result. To process the ash, water is first added to the mixture and left to settle for a couple hours. The solution is drained and dried and the result is ash containing less harmful chemicals like some soluble alkalis.

Science

Wood ash is primarily made up of calcium carbonate, which is used in many glaze recipes and has a low melting point, making it possible to use as a glaze. The ash also contains potassium carbonate, phosphates, and other metals; however, the ratio of these chemicals depend on the location, soil, and type of wood the ash came from. The different chemical compositions make the glaze to produce different results from batch to batch. Furthermore, two pieces with the same glaze batch can even have different results. If the ash its not cleaned or mixed thoroughly, some parts of the glaze mixture can have more of one chemical and others could have more of another making each part of the glaze to actually have varying concentrations of chemicals.

See also

• Ceramic glaze
• Pottery
• Raku Ware
• Celadon
• Shino (glaze)
• Onggi
• Chinese ceramics