Published: June 14, 2018 • By Jeff Gingras and Debby Sneed

The primary raw material in the production of pottery is clay, a hydrous aluminum silicate (Al2O3·2SiO2·2H2O). It is formed by the decomposition of igneous rock through both chemical and physical processes (1).

Clay is a plastic substance and its plasticity allows it to be worked into a variety of shapes. There are two main types of clay: primary and secondary. Primary or residual clays are clays that have not been moved from their place of formation, making them the purest form of clay and also the most rare. Primary clays are the most difficult to work or mold by themselves, as they have little plasticity and they require the addition of a more plastic material to make them workable. Primary clays fire at the highest temperatures, are white in color, and mostly coarse-grained in texture. 

Secondary or sedimentary clays have been moved from their place of formation by the actions of water (in which case it is called ball clay) or wind and by erosion (in which case it is called fire clay). These clays fire at lower temperatures, are not white, and are much more plastic than primary clays. 

The clay beds in the Mediterranean regions are mostly secondary clays. The composition of secondary clays differs depending not only on the parent rock but also on impurities that the clays gathered on their movement from their originating location to their final stratum and, for this reason, the sources of these clays can often be distinguished from one another. The clay from the region of Attica, for example, fires to a red-orange color because of the presence of iron oxides, while Corinthian clay, which has fewer iron oxides, fires to a light yellow color. 

Footnote

  1. Toby Schreiber, Athenian Vase Construction: A Potter's Analysis (Malibu: The J. Paul Getty Museum, 1999): 3-8.

References

  • J.V. Noble, "An Overview of the Technology of Greek and Related Pottery" in ed. H. A. G. Brijdger, Ancient Greek and Related Pottery: Proceedings of the International Vase Symposium in Amsterdam, 12 -15 April 1984 (Amsterdam: Allard Pierson Museum, 1984): 31. 
  • J.V. Noble, The Techniques of Painted Attic Pottery (London: Thames and Hudson Ltd., 1988).
  • Susan Peterson, The Craft and Art of Clay (Englewood Cliffs, N.J.: Prentice Hall, 1996): 130 - 53. 
  • Toby Schreiber, Athenian Vase Construction: A Potter's Analysis (Malibu: The J. Paul Getty Museum, 1999).
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