A short ceramics glossary for beginners

Slip, leather-hard, bisque, trimming… Ceramics vocabulary can be confusing at first. Here are the words you'll come across most often on the forum.

Clay and its stages

• Clay or clay body: the raw material.
• Grog: clay that has been fired and then ground, added to clay to reduce shrinkage and warping, and to make it more resistant to thermal shock.
• Slip: clay thinned with water, used as “glue” to join parts together.
• Engobe: liquid clay, often tinted, applied to the piece to decorate it.
• Leather-hard: the piece has partly dried; it's firm but still slightly flexible. This is the right time to trim, attach a handle or carve a decoration.
• Bone-dry: the piece has lost its water; it's paler and fragile. It's ready for the first firing. Until it's fired, it can still be reclaimed.
• Shrinkage: clay shrinks as it dries, then as it's fired. The percentage is given by the manufacturer, and our shrinkage calculator helps you predict the final size.

Forming

• Throwing: shaping a piece on a spinning potter's wheel.
• Centering: the first step of throwing, which means getting the clay perfectly in the middle of the wheel.
• Trimming: putting a leather-hard piece back on the wheel to refine the walls and form the foot.
• Hand-building: shaping by hand, without a wheel.
• Coil: a rope of clay stacked up to build a piece.
• Slab: clay rolled out flat, cut and then assembled.
• Rib: a small flat tool, made of wood, metal or rubber, used for smoothing and shaping.

Firing and glaze

• Bisque (bisque firing): the first firing, which makes the piece strong but still porous. It's called a low bisque when it's done at a low temperature, before a higher glaze firing (stoneware, porcelain).
• Glaze: a mixture of minerals applied to the piece, which melts during firing and forms a glassy layer.
• Underglaze: a pigment applied under a clear glaze.
• Cone: a small ceramic indicator that bends to show the heatwork received during firing.
• Hold: the period when the kiln is held at a given temperature.
• Oxidation, reduction: firing with plenty of or little oxygen in the kiln. Electric kilns fire in oxidation.
• Loading, unloading: putting pieces into the kiln, then taking them out.

Is there a word you don't know? Ask in this category: there are no silly questions here.