Porcelain Glossary
Every term you'll encounter while learning porcelain, explained in plain language.
Bat
A disc (plaster or wood) that attaches to the wheel head. Makes it easy to remove pieces without distorting them.
Bisqueware
Clay that has been fired once (bisque fire) but not yet glazed. Porous enough to absorb glaze, but strong enough to handle safely.
Bone-dry
Clay that has lost all its moisture and is ready for bisque firing. Feels chalky and cool to the touch. Very fragile at this stage.
Centering
Getting clay perfectly centered on a spinning pottery wheel. The foundation of all wheel throwing, and the hardest part for beginners.
Cone
A small pyrometric device that bends at a specific temperature. Used to measure kiln heat accurately. Higher numbers mean higher temperatures. Cone 06 is low-fire (~1000°C), Cone 10 is high-fire (~1300°C).
Crazing
Fine cracks in a glaze surface caused by the glaze and clay shrinking at different rates during cooling. Makes a piece unsuitable for food use because bacteria can grow in the cracks.
Feldspar
A mineral that acts as a flux in porcelain. It melts during firing and fills the gaps between kaolin and silica particles, creating the glassy matrix that makes porcelain dense and translucent.
Flux
A material that lowers the melting point of silica, enabling glass formation at achievable kiln temperatures. Feldspar is the primary flux in porcelain.
Foot ring
The raised ring on the bottom of a pot, created during trimming. Keeps the pot stable on a surface and elevates the base.
Greenware
Unfired clay pieces at any stage of drying, from freshly formed to bone-dry. Extremely fragile and will dissolve if re-wetted.
Grog
Ground-up, pre-fired clay added to a clay body. Reduces shrinkage and adds structural strength, but makes the surface rougher.
Kaolin
The purest form of clay and the primary ingredient in porcelain. Named after Gaoling village in Jingdezhen, China. Fires white, but has low plasticity, which is why porcelain is challenging to work with.
Kiln wash
A protective coating applied to kiln shelves. Prevents glaze drips from permanently fusing pieces to the shelf during firing.
Leather-hard
The stage where clay is partially dry: firm enough to hold its shape but soft enough to carve, trim, or attach pieces. Feels cool and slightly damp. The ideal stage for trimming and adding handles.
Mullite
A mineral that forms within porcelain during high-temperature firing. Its needle-like crystals create the dense structure that gives porcelain its remarkable strength.
Plasticity
How stretchy and workable a clay is. High plasticity means easy to shape. Porcelain has relatively low plasticity compared to earthenware or stoneware, which is why it requires more skill.
Score and slip
The technique for joining two pieces of clay. Score (scratch) both surfaces deeply, apply slip (liquid clay) as glue, press firmly together, and smooth the seam. Essential for any attachment.
Silica
Silicon dioxide (quartz). The structural backbone of porcelain. Provides integrity, controls shrinkage, and helps glazes adhere properly.
Slip
Clay mixed with water to a creamy consistency. Used as glue for joining pieces, as a decorative coating, or for casting in plaster molds.
Throwing
Shaping clay on a spinning pottery wheel. The name comes from the Old English word meaning to twist or turn.
Vitrification
The process by which clay particles fuse together at high temperatures, becoming dense, glassy, and non-porous. Fully vitrified porcelain is waterproof even without glaze.
Wedging
Kneading clay to remove air bubbles and create a uniform consistency. Essential before any forming work. Similar to kneading bread dough, but with a specific technique.
Ball clay
A very plastic, fine-grained clay often added to porcelain bodies to improve workability. Introduces slight color (grey or cream) but makes the clay much easier to shape.
Burnishing
Polishing leather-hard clay with a smooth stone or the back of a spoon. Compresses the surface particles, creating a soft sheen without glaze.
Calipers
A measuring tool used to check dimensions, especially for matching lids to pots. Set the calipers to the inside diameter of the pot, then use them to size the lid.
Cold porcelain
A modeling compound made from cornstarch and PVA glue that air-dries at room temperature. Not actual porcelain or ceramic. Popular for flower sculpting because it dries translucent when thin.
Coil building
A hand-building technique where ropes of clay are stacked and smoothed together to build walls. One of the oldest pottery methods, capable of producing large forms without a wheel.
Deflocculation
Adding a small amount of an alkaline substance (like sodium silicate or vinegar) to clay or slip to make it more fluid without adding more water. Used in slip casting and as a throwing aid.
Engobe
A colored clay slip applied to the surface of a piece for decoration. Similar to underglaze but contains more clay. Applied at the leather-hard or greenware stage.
Glaze fit
How well a glaze and clay body match in their rates of thermal expansion. Good fit means no crazing or shivering. Mismatched fit causes defects during cooling.
Kiln furniture
The shelves, posts, and stilts used inside a kiln to stack and separate pieces during firing. Made from refractory materials that withstand extreme heat.
Overglaze
Decoration applied on top of an already-fired glaze surface, then fired again at a lower temperature (750-900°C). Allows vivid colors including reds and gold that can't survive higher temperatures.
Paperclay
Clay mixed with cellulose fiber (from paper pulp). Much more forgiving than regular clay - resists cracking, can join wet to dry, and is easier to repair. Available in porcelain bodies.
Pinching
The simplest hand-building technique. Shape a ball of clay using only your thumb and fingers, pinching and rotating to form walls. Every potter's first technique.
Pyrometric cone
A small cone-shaped indicator placed inside a kiln that bends at a specific combination of heat and time (heat work). More accurate than temperature alone because clay responds to both.
Quartz inversion
A critical point at 573°C where silica crystals suddenly change structure, causing a slight expansion (heating) or contraction (cooling). Requires careful kiln management to avoid cracking.
Reduction firing
Firing with restricted oxygen (usually in a gas kiln). Starving the kiln of oxygen changes glaze colors dramatically - copper goes from green to deep red, iron from brown to blue-grey.
Sgraffito
A decoration technique where you scratch through a layer of colored slip or underglaze to reveal the contrasting clay body beneath. From the Italian word meaning to scratch.
Shrinkage
The reduction in size that occurs as clay dries and fires. Porcelain shrinks 12-18% total from wet to fired, which is more than stoneware (10-14%). Always make pieces larger than your target size.
Slab building
A hand-building technique using flat sheets of clay cut and assembled into forms. Good for geometric shapes like boxes, plates, and tiles. Roll even slabs using guide sticks.
Soaking
Holding the kiln at peak temperature for a period of time (10-30 minutes) to allow even heat distribution and complete glaze maturation. Also called a hold.
Stoneware
A mid-to-high-fire clay body (1200-1300°C) that is durable, non-porous, and usually grey or brown. The most common clay for functional pottery. More forgiving than porcelain for beginners.
Trimming
Carving excess clay from the base and foot of a leather-hard piece, usually on the wheel. Creates the foot ring and refines the profile. Done when clay is firm but still carvable.
Underglaze
Colored decoration applied to bisqueware or greenware before the clear glaze coat. Fired together in the glaze firing. Allows precise painting and stable colors. Available as liquids, pencils, and chalks.
Wax resist
A technique where liquid wax is brushed onto areas where you don't want glaze. The glaze slides off the waxed surface, creating clean patterns and protecting the foot from glaze.