Ash glazes are ceramic glazes which were formulated from wood-ash .

Appearance

The glaze has glasslike and pooling (the builds up of glaze) characteristics which puts emphasis on the surface texture of the piece being glazed. 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. 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

Kiln

A kiln is a thermally insulated chamber, or oven, in which a controlled temperature regime is produced. Uses include the hardening, burning or drying of materials...

 (an oven-like structure used to turn the ceramic

Ceramic

A ceramic is an inorganic, nonmetallic solid prepared by the action of heat and subsequent cooling. Ceramic materials may have a crystalline or partly crystalline structure, or may be amorphous...

 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

Wood ash

Wood ash is the residue powder left after the combustion of wood. Main producers of wood ash are wood industries and power plants.-Composition:...

 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 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 ware is dramatically safer than using plastic ware because of its lack of carcinogens, cancer causing materials.

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

Sieve

A sieve, or sifter, separates wanted elements from unwanted material using a woven screen such as a mesh or net. However, in cooking, especially with flour, a sifter is used to aerate the substance, among other things. A strainer is a type of sieve typically used to separate a solid from a liquid...

, 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. 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
  Ceramic glaze
  Glaze is a layer or coating of a vitreous substance which has been fired to fuse to a ceramic object to color, decorate, strengthen or waterproof it.-Use:...
  
  
• Pottery
  Pottery
  Pottery is the material from which the potteryware is made, of which major types include earthenware, stoneware and porcelain. The place where such wares are made is also called a pottery . Pottery also refers to the art or craft of the potter or the manufacture of pottery...
  
  
• Raku Ware
• Celadon
  Celadon
  Celadon is a term for ceramics denoting both a type of glaze and a ware of a specific color, also called celadon. This type of ware was invented in ancient China, such as in the Zhejiang province...
  
  
• Shino (glaze)
  Shino (glaze)
  is a generic term for a family of pottery glazes. They tend to range in color from milky white to a light orange, sometimes with charcoal grey spotting, known as "carbon trap" which is the trapping of carbon in the glaze during the firing process...
  
  
• Onggi
  Onggi
  Onggi are Korean ethnic earthenware, which were extensively used as tableware as well as storage containers in Korea. It includes both unglazed earthenware fired near 600~700°C and pottery with a dark brown glaze that burnt over 1100°C....
  
  
• Chinese ceramics