FYI Friday (Clay Terms)



In the field of ceramics there are a number of terms or words used to describe what may be happening in your work. You may encounter a few of these in the process of troubleshooting glazes, making your pots, or purchasing new tools. Here, we’ll compile a list of the most common ceramic terminologies and their meanings to help in your future searches.


  • Absorbency: The ability of clay to soak up water, like a sponge.
  • Bone Dry: Dehydrated, unfired clay that is brittle and cool to the touch.
  • Bisque Firing: The initial firing after a piece of clay has completely dried, which turns greenware clay into ceramic. This firing usually occurs between cone 010 (approx.. 1657°F) to cone cone 04 (approx. 1945°).
  • Bisqueware: Clay that has undergone a transformative chemical process in which it is heated to a point that it is no longer soluble in water. The piece is now considered ‘ceramic’ at this point.
  • Ceramic: A clay object that has been bisque fired.
  • Clay: Decomposed rock containing many fine particles of hydrous aluminum, silicates and other minerals, which is used for brick, tile, and pottery; specifically.
  • Clay Body: A mixture of two or more clays and minerals combined to obtain a desired color, plasticity, strength, fired density or other properties.
    • Earthenware: Low fire clay, still porous after firing. Cone range: 04-06
    • Stoneware: Mid-range to high fire clay that vitrifies after cone 5. Cone range: 5-10
    • Porcelain: High Fire Clay, vibrant white in color, translucent when thin. Cone range: 8-12
  • Firing: The process in which clay and glazes are heated to maturity (or at least beyond the point in which they are soluble in water)
  • Greenware: Un-fired pottery.
  • Grog: Clay that has been fired and then ground into ganules for ore or less fineness. Grog is considered a filler and added to clay bodies to promote even drying, reduce shrinkage, and give stability.
  • Hand Building: A broad term which describes a variety of methods in which a piece is built by hand, either by pinching, coiling, slab building
    • Coiling: Creating forms by adding rope-like coils of clay to form the base and walls of the vessel.
    •    Pinch Pot: Forming in which a ball of clay is pressed, pulled, and pinched into a desired shape by the thumb and fingers.
    • Slab Method: A method of forming in which the clay is rolled out into sheets of a desired thickness, cut, and joined together using the slip and score method.
  • Kaolin: A china clay in its purest form.
  • Leather Hard: The drying between wet and bone dry, in which clay has lost some of its water content but remains firm and pliable; the ideal stage for trimming, carving and adding additions, like handles.
  • Mature: Clay that has been fired to a tight, hard, serviceable structure.
  • Plasticity: The quality that allows clay to be stretched, shaped and manipulated.
  • Short: Nonplastic clay, poor working qualities.
  • Shrinkage: The decrease in size of a clay object due to drying and firing.
  • Slake: To moisten dry clay with water.
  • Slip and score: A joining technique where the two edges to be attached are scratched and adhered with a liquid clay (slip).      
    • Slip: Clay that is diluted with water to a point where it can be applied with a brush, like a paint or glue. Slip can be made from the same clay body to join two or more pieces together or colorants can be added for decorative purposes.
    • Slip casting: a process in which liquid clay is poured into a plaster mold to take the shape of an object.
  • Thermal Shock: Breakage of a ceramic piece caused by a sudden change in temperature. Each distinct clay body has its own level or resistance to thermal shock
  • Vitrification: A glass-like state of consistency, in which the clay has completely hardened and matured.
  • Wedging: kneading the clay to make the clay homogenous, to align the particles, and to remove air pockets.



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