Shrinkage occurs in the production of pottery and affects pottery at two stages in the process, during both drying and firing. During the drying stage, the wet clay loses its water and contracts, producing the first phase of shrinkage. Although a vessel may feel dry to the touch after drying in the open air for weeks, it still contains chemical water in its fabric and, therefore, the process of water loss and shrinkage continues during firing. The final dried-and-fired product, then, will be smaller than the vessel immediately after it was formed from wet clay.
Different clay bodies have different rates of shrinkage based on the amount of actual clay they contain. A potter must know the shrinkage rate of their clay body so that they can adjust the shrinkage rates of the glaze or slip decoration to fit. If the potter fails to do this, the clay body and glaze or slip will shrink at different rates. If slip has a different shrinkage rate than the clay body, for example, it will flake off. If glaze, however, has a lower shrinkage rate than the clay body, the result is called crazing, a process that produces fine cracks on the surface. The opposite, shivering, is when glaze comes off the vessel or cracks it (1).
This essay was written to accompany a collection of Greek artifacts at the CU Art Museum.
Footnote
- Susan Peterson, The Craft and Art of Clay (Englewood Cliffs, N.J.: Prentice Hall, 1996); Toby Schreiber, Athenian Vase Construction: A Potter's Analysis (Malibu: The J. Paul Getty Museum, 1999): 24-5, 203.