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Bloating in a high iron raw clay ground to 42 mesh (Plainsman M2). It is still stable, dense and apparently strong at cone 4 (having 1.1% porosity). But at cone 6 (top bar) it is bloating badly. At cone 5 the clay experiences the early stages of bloating. Cone 4 is thus "dangerous territory" for this particular clay. A reminder of this can be seen by putting on a transparent glaze - it fills with clouds of micro-bubbles from off-gassing that has begun well below cone 4.
| Troubles | 
Over Firing of Ceramic Glazes and Bodies
 Overfiring can happen with glaze, engobes or clay bodies. The problem is more subtle than you might think.  | 
| Troubles | 
Bloating
 Bloating occurs when the off-gassing of decomposing particles in a body has not completed by the onset of density and impermeability associated with the vitrification process.  | 
| Glossary | 
Clay Body Porosity
 In ceramics, porosity is considered an indication of density, and therefore strength and durability. Porosity is measured by the weight increase when boiled in water.  | 
| Glossary | 
Vitrification
 A process that happens in a kiln, the heat and atmosphere mature and develop the clay body until it reaches a density sufficient to impart the level of strength and durability required for the intended purpose. Most often this state is reached near zero p  | 
| Glossary | 
Terra Cotta
 A type of red firing pottery. Terra cotta clay is available almost everywhere, it is fired at low temperatures. But quality is deceptively difficult to achieve.  | 
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