What a clay body is
Raw clay dug from the ground is rarely used on its own. Suppliers blend clays with other minerals, such as silica and feldspar, to get a mix that is easy to shape and that fires the way they want. That mix is the clay body. It arrives as moist clay in a sealed bag, ready to use after a little wedging.
Every bag or data sheet lists a firing range, usually as a cone number. Cones are explained in the firing guide. For now, the key idea is simple: fire the clay too low and it stays weak and porous; fire it too high and it can slump, bloat or melt.
The three main families
| Clay body | Typical firing | After firing | Good for beginners because |
|---|---|---|---|
| Earthenware | Low fire, around cone 06 to 04 | Often red or buff, slightly porous, softer | Forgiving to shape, bright glazes, lower kiln temperatures |
| Stoneware | Mid fire (cone 5 to 6) or high fire (cone 9 to 10) | Dense, strong, close to watertight | Sturdy for daily use, wide choice of glazes |
| Porcelain | Mid or high fire | White, hard, can be translucent where thin | Beautiful results once you have some control |
Earthenware
Earthenware is the classic flowerpot clay. Iron in many earthenware bodies gives the warm terracotta color. Because it is fired at lower temperatures, it never fully closes up, so it stays a little porous. A good glaze seals the surfaces that touch food or water, but an unglazed foot can still soak up moisture.
Stoneware
Stoneware is fired hot enough to vitrify, which means the particles partly melt and fuse into a dense body. It is the usual choice for mugs, bowls and plates. Many community studios use a mid-fire stoneware because it suits electric kilns and gives sturdy pots.
Porcelain
Porcelain is made mostly from kaolin, a fine white clay. It is smooth and lovely to touch, but it is less forgiving than stoneware: it can feel floppy on the wheel, it warps more easily, and it shows every fingerprint. Many teachers suggest starting with stoneware and trying porcelain later.
Grog, sand and texture
Grog is fired clay crushed into small grains. Mixed into a clay body, it adds tooth, helps a pot hold its shape, lets thick pieces dry more evenly and reduces cracking. Groggy clays are popular for hand building and sculpture. Smooth clays with little or no grog are kinder to your hands on the wheel. The bag usually says whether a body is smooth, fine grog or coarse grog.
Clay shrinks
Clay gets smaller as it dries and again as it fires. Total shrinkage is often somewhere around 10 to 15 percent, but it varies a lot between bodies, so check the supplier's data sheet. Shrinkage matters when you make lids, sets or anything that has to fit something else. Make the parts from the same clay, at the same time, and dry them together.
Match clay, glaze and kiln
- Your clay and your glaze need to suit the same cone. A low-fire glaze on a high-fire clay may run off the pot. A high-fire glaze on earthenware can leave the clay overfired and slumped.
- Your kiln must reach that cone. Check its maximum in the kiln maker's manual.
- In a shared studio, use the clays the studio approves. Unknown clays can melt onto kiln shelves and ruin other people's work.
- Keep clays separate. Mixing a red earthenware into a white stoneware changes how both behave.
Air-dry and oven-bake clays are craft materials, not ceramic. They never go through a kiln, and they are not suitable for holding food or drinks.
Next step
Once you have a clay, wedge it and start shaping. The hand building guide needs the least equipment, and the wheel throwing guide covers the potter's wheel.