Types of pottery cracking
- Types of pottery cracking
Cracking results from stress within a ceramic body. This can be due to expansion, contraction, and shrinkage and how the work responds to these stressors. Poor drying or uneven compression and alignment of particles in the making can result in an inability to with stand stressors and resulting cracking. Cracking may appear in greenware as well as each stage of the firing including bisque ware and glazed ware.
Cracking in greenware resulting in stresses during the making. To avoid cracks in greenware uniformity should be maintained in the thickness of the pot, the drying of the greenware, as well as consistancy of the clay body itself. Cracks can result in uneven drying from thinner to thicker spots within the pot. A lack of compression in the bottom while throwing results in a commonly seen "s" crack on the underneath of the pot.
Cracks caused by thermal shock called dunting occur during the firing process and are witnessed in the bisqued ware stage. Dunting is a problem that commonly occurs during the cooling process of the firing cycle. Latent or dormant cracks which went unnoticed in greenware may appear in bisqued ware after firing.
A crack that appears in any stage of firing increasing gets worse through multiple firings. Cracks may also go unnoticed until after the glazed firing. In glazed ware the glaze becomes a stressor due to the thermal expansion. The interaction of the glaze and the clay body causes stress on the pot in glaze firing.
References
*Fraser, Harry. Ceramic Faults and their Remedies. A and C Black. London. 1986.
*Hamer, Frank and Janet. The Potter's Dictionary of Materials and Techniques, Fifth Addition. University of Pennsylvania Press. Philadelphi. 2004.
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