Dunting is a fault that can occur during the firing of
ceramic
A ceramic is any of the various hard, brittle, heat-resistant, and corrosion-resistant materials made by shaping and then firing an inorganic, nonmetallic material, such as clay, at a high temperature. Common examples are earthenware, porcela ...
articles. It is the "
cracking
Cracking may refer to:
* Cracking, the formation of a fracture or partial fracture in a solid material studied as fracture mechanics
** Performing a sternotomy
* Fluid catalytic cracking, a catalytic process widely used in oil refineries for crac ...
that occurs in fired ceramic bodies as a result of a
thermally induced
stress
Stress may refer to:
Science and medicine
* Stress (biology), an organism's response to a stressor such as an environmental condition
* Stress (linguistics), relative emphasis or prominence given to a syllable in a word, or to a word in a phra ...
" and is caused by a "ware cooled too quickly after it has been
fired".
Although usually occurring during, cooling dunts can also be caused by excessively fast heating rates. Heating dunts can be recognised by rounded edges to the cracks as the
glaze matured after they occurred, whereas cooling dunts have sharp edges.
It has been found that bodies formulated with
quartz
Quartz is a hard, crystalline mineral composed of silica (silicon dioxide). The Atom, atoms are linked in a continuous framework of SiO4 silicon–oxygen Tetrahedral molecular geometry, tetrahedra, with each oxygen being shared between two tet ...
rather than
flint
Flint, occasionally flintstone, is a sedimentary cryptocrystalline form of the mineral quartz, categorized as the variety of chert that occurs in chalk or marly limestone. Historically, flint was widely used to make stone tools and start ...
were more susceptible to dunting, especially on re-fire. It was postulated this may be related to the lower
Young's modulus
Young's modulus (or the Young modulus) is a mechanical property of solid materials that measures the tensile or compressive stiffness when the force is applied lengthwise. It is the modulus of elasticity for tension or axial compression. Youn ...
of the quartz based bodies.
Dunting also occurs in wares produced from montmorillonite clay bodies due to the volume expansion of
cristobalite
Cristobalite ( ) is a mineral polymorph of silica that is formed at very high temperatures. It has the same chemical formula as quartz, Si O2, but a distinct crystal structure. Both quartz and cristobalite are polymorphs with all the members o ...
during its inversion upon cooling. "The release of free silica, takes place in montmorillonite above 950 C, but almost double the silica is released, compared to kaolin. Therefore, clay bodies with high amounts of montmorillonite contain a high percentage of free silica after firing, which may cause the ware to crack during cooling.(Dunting)"
["Clay Materials - For the self reliant potter", Henrik Norske. ''GTZ'' 1990; 98 pages]
See also
*
Pottery
Pottery is the process and the products of forming vessels and other objects with clay and other raw materials, which are fired at high temperatures to give them a hard and durable form. The place where such wares are made by a ''potter'' is al ...
*
Ceramics (art)
Ceramic art is art made from ceramic materials, including clay. It may take varied forms, including artistic pottery, including tableware, tiles, figurines and other sculpture. As one of the plastic arts, ceramic art is a visual art. Wh ...
References
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Pottery
Ceramic engineering