ceramic technology and analysis. clay and temper preparation
Post on 16-Dec-2015
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Temper
• As the clay in pottery dries, or is fired, the loss of water causes compaction of the clay platelets, which may cause cracking.
• Temper is a material that is added to clay that resists shrinkage and is also refractory under the conditions of firing. It can take many forms, including grog, which is ground-up sherds.
Vessel Formation TechniquesTechnique Appearance
Pinching Thick-walled lumpy bowl Paddle and Anvil Irregular surface and shape
Slab Cylindrical shape
Coil Smooth sided, asymmetrical
Mold visible seam, appearance
identical to other vessels.
Slow and Fast Wheels finger striations in interior,
symmetrical profile, thin walls in the case of fast wheel.
Steps in Vessel Formation1. Digging and preparing clay, adding
temper.
2. Forming the base (sometimes a mold is used, e.g. a basket).
3. Forming the walls, including scraping.
4. Applying impressed decoration while clay is still plastic.
5. Slipping pot while it is still damp.
Degrees of Firing
Temperature Term Appearance
Sun baked Adobe mud w/ straw
Below 900˚ Terra Cotta roof tiles
900˚-1200˚ Earthenware pottery
1200˚-1350˚ Stoneware Asian pottery
Above 1300˚ Porcelain Fully vitrified
Term: vitrification – to convert into glass
Terms Related to Firing Environment
• Oxidizing: a free flow of oxygen reaches the vessels during firing. Minerals in the paste, slip, and paint are converted to their oxide forms, causing color changes.
• Reducing: Oxygen is cut off to the fire during the latter stages of the firing process. Additional carbon may be thrown onto to fire beforehand, and the carbon is driven into the fabric of the pot, turning it black. Minerals turn into their unoxidized forms.
Jar
Ollas
Mug
Vase
Generally vases and mugs have unrestricted orifices (though the mug above has a restricted orifice), ollas and jars have restricted orifices.
Pitcher
Bowl
Amphora
Comal
Note that it is common to paint the inside of a bowl.
Common Ceramic Terms Relating to Vessel Form
base base
rim rim
neck neck
shoulder*
*referred to as the upper body by Anna Sheppard
orifice orifice
body
Asian Ceramic Technology: Han Dynasty 206 BCE – 220 AD
• Lead glazed pottery: low-fired pottery that uses powdered lead oxide as fluxing agent, mixed with quartz in a ratio of 3:1. Small amounts of copper were added that turned green when oxidized, or iron which turned brownish-yellow.
• Celedon: an innovation of the the 1st century AD within the Eastern Han dynasty. Celedon is to be equated with porcelain in that it is fully vitrified.
• The green color of celedon glaze was achieved by iron
oxide and wood
ash fired in a
reducing
atmosphere.
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