Dunting is cracking caused by stress while a kiln heats or cools, especially through quartz inversion around 573 °C. Dunts are usually clean, sharp cracks that can run right through the clay and glaze.
What Is Dunting?
Clay contains silica, and some forms of silica change volume suddenly at particular temperatures. Digitalfire explains that if one part of a piece passes through quartz inversion before another part, because it is thinner, closer to an element or sitting on a heavy shelf, the difference in contraction can crack it.
Cooling dunts have sharp edges with glaze that hasn’t flowed over them, because the glaze was already solid when the crack opened. Heating dunts happen on the way up, and the glaze often rounds over the crack edges because it melted afterwards. Reading the crack tells you when it happened.
Prevention means slowing heating and cooling through the inversion range, keeping walls and bases an even thickness, leaving space around pieces and elements, and not opening the kiln early. A glaze that fits the clay poorly, or glaze applied thickly to one side only, adds stress and makes dunting more likely, especially on wide plates and platters.
This pottery glossary entry from Le Studio Art Space is general educational content. Always follow the clay, glaze and kiln makers’ data for your own materials and equipment.