Clay Bodies

The body almost everything in this log is thrown from. It is plastic enough to pull a 30 cm cylinder without a fight, matures over a wide enough range that a cone either side of target still gives a saleable pot, and takes both a celadon and an iron satin without either one running off.

Default choice. Reach for it unless you have a specific reason not to.

Bars compare the four bodies on this page only, on a 0 to 100 relative scale. They are not engineering values.

Where it earns its place

• Wide maturity range: cone 5 through cone 10 all produce a usable, vitrified body.
• High green strength, so trimming, hand-building onto a leather-hard form and pulling handles all work on the same day.
• Thermal-shock tolerant enough for ovenware and for a teapot that gets a pre-warm and a top-up.
• Forgives a slightly uneven wall, which is why it is the body to learn on.

Where it will let you down

• At cone 10 a dark stoneware body will fight a pale glaze; the iron in the clay shows through wherever the glaze thins.
• Shrinkage of 10 to 12 percent means every dimension you throw is roughly a tenth larger than the finished piece.
• Not translucent. If you want light coming through the wall, this is the wrong bag.

Porcelain is not a harder stoneware, it is a different material with different failures. It has almost no plasticity, so it cannot be pushed — it has to be coaxed up in one continuous motion with wet hands and no second attempts. What it gives back is a wall that goes translucent at 3 mm and a colour that no stoneware can reach.

Use it when the piece is about translucency or colour. Do not use it to save time.

Bars compare the four bodies on this page only, on a 0 to 100 relative scale. They are not engineering values.

Where it earns its place

• Translucency. A 3 mm porcelain wall passes light; a stoneware wall of the same thickness does not.
• The only body that gives a true celadon — the blue-green depends on light travelling through a white, iron-free glass.
• Takes a razor edge when trimmed, which is what makes a porcelain teabowl feel thinner than it is.
• Vitrifies completely at cone 10, so a well-fired piece is non-porous with no glaze at all.

Where it will let you down

• Shrinkage of 12 to 15 percent is the highest of the four, so measurements made on the wheel are further from the finished size than anywhere else.
• Almost no green strength when thin: a 3 mm wall will not survive being picked up by the rim before bisque.
• Crazes easily with high-expansion glazes, and a crazed porcelain surface is a poor choice for food that will stand.
• A very small window between "not mature" and "slumped".

Low-fire earthenware does not vitrify: the fired body stays porous and that is the point, not a defect. It is the most plastic body here, which makes it the easiest to throw and the easiest to hand-build, and it is the only body where a full range of bright low-fire colours is cheap and reliable.

Use it for low-fire colour, for prototypes, and for work that will live indoors.

Bars compare the four bodies on this page only, on a 0 to 100 relative scale. They are not engineering values.

Where it earns its place

• The most plastic body of the four — coil building, slab work and throwing all behave predictably.
• Lowest shrinkage, so the piece you make is closest to the piece you get.
• Bright, stable colour: cobalt, chrome-tin and copper all work cleanly in oxidation at cone 04.
• Cheap enough to prototype a form five times before committing to a better body.

Where it will let you down

• Porous and not frost-proof. Outdoor work in a freezing climate will spall.
• The fired body is soft: it scratches, and a knife will mark a plate.
• Because it is not vitrified, an unglazed earthenware surface stains and holds odours.
• Glazes craze easily on it — the body and a frit base can have very different expansion.

A raku body is engineered backwards from one event: being pulled glowing from the kiln and plunged into cold air. Everything in it — 30 to 40 percent coarse grog, a high sand fraction, a deliberately open texture — exists to let it survive that one thermal shock. It is not a general-purpose clay and should never be used as one.

Only for raku. Do not put it on the wheel for sale work, and do not put food in it.

Bars compare the four bodies on this page only, on a 0 to 100 relative scale. They are not engineering values.

Where it earns its place

• Extreme thermal-shock resistance; a grogged raku body will take a water quench straight from 900 °C without cracking.
• Low shrinkage and an open texture mean thick, sculptural forms dry without the cracks a plastic body would give.
• Grog gives grip, so pinch pots and slab forms hold their shape without slumping.
• Its cheapness and its tolerance of abuse make it the body to experiment on.

Where it will let you down

• Not watertight, not food-safe and not frost-proof. A raku vessel is a dry vessel.
• The open texture makes it unpleasant to throw fine work on; it tears at thin rims.
• Glaze fit is unpredictable because the firing is deliberately incomplete.
• The firing itself is the hazard: open flames, glowing metal bins and pieces that can explode in tongs.