Ash glaze
Ash glazes are ceramic glazes which were formulated from wood-ash.[citation needed]
Appearance
The glaze has glasslike and pooling (build 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.[citation needed]
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. Ash glaze was one of the first glazes used and contained only ash, clay, and water.[1][2]
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 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.
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 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 results. 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.[3]
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 is 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.[4]
See also
References
- ↑ Rogers, Phil. Ash Glaze. University of Pennsylvania Press; 2nd edition. (2003)
- ↑ Lombardo, Daniel. 2003. "Ash Glazes (Book)." Library Journal 128, no. 19: 66. Academic Search Complete, EBSCOhost (accessed January 19, 2010).
- ↑ Svoboda, Petra. "Earth, Soil, Mud, Clay - Processing Progression" Australian Ceramics. 7 Feb. 2010 http://www.australianceramics.com/JUNE/tech_ps.html
- ↑ Svoboda, Petra. "Earth, Soil, Mud, Clay - Processing Progression" Australian Ceramics. 7 Feb. 2010 http://www.australianceramics.com/JUNE/tech_ps.html
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