Coil building is the slowest and the most reliable way to make a large pot, and it fails for one of two reasons: the coils are joined when the wall below is still soft, or the wall is allowed to dry too fast between sessions. A 30 cm earthenware pot takes four sessions across three days. That sounds excessive until you watch a pot collapse at 25 cm because the second session started an hour too early.
H 30 · Ø20 / Ø24 / Ø12 cm
Session one: base and first four coils
Roll a 1.5 cm thick slab for the base and cut a 14 cm disc. Compress it with a rib, then score the outer 2 cm in a crosshatch. Roll coils 1.5 to 2 cm in diameter, no longer than 25 cm at a time, and let them rest 10 minutes before using them — a fresh coil stretches and thins as it is bent around the base.
Join each coil to the one below with a 45 degree diagonal weld, not a horizontal butt joint. Crosshatch both surfaces, apply slip, press the coil down with thumb and forefinger, then blend the join with a wooden tool on both the inside and the outside. Four coils takes the wall to about 8 cm high. Then cover the whole pot with a plastic bag and stop for the day.
Between sessions: the stiffening test
The pot must be leather-hard all the way round before the next coil goes on. Press a fingernail into the wall at three heights. If the nail leaves a mark that springs back, it is too soft: leave it another hour. If the mark stays crisp and white, it is ready. Twelve to eighteen hours under plastic in a 20 degree room gets a 6 mm earthenware wall there.
Do not unwrap the pot during the wait. The bag keeps the rim from drying faster than the wall, and a rim that dries first will crack before the second session begins.
Sessions two to four: the shaping pass
Add three or four coils per session, always joining in the same direction (work clockwise if the first session was clockwise; alternating directions leaves a helical weakness). After every two coils, run a rib up the inside and outside to bring the wall to shape and to compress it — 6 mm for a 30 cm pot is right, 4 mm will slump.
Support the growing wall from the outside with one hand while shaping. Above 20 cm the wall carries no load of its own and will move under the lightest pressure. If the profile has drifted, correct it in a shaping pass at the start of the next session rather than mid-coil.
Finishing and slow drying
After the last coil, form the rim by rolling the top edge inward between finger and thumb, then compress it with a rib. A coiled rim that is not compressed will open along the coil line in the bisque firing, which is the single most common failure of coil-built pots.
Dry the finished pot under loose plastic for five days, unwrapping gradually: 24 hours with a small hole in the bag, 48 hours with two larger holes, then a day bare in a cool room. Fast drying is what cracks open coiled work, and the cracks appear at the coil joins, where the shrinkage difference is greatest.
Steps
- Roll a 1.5 cm slab, cut a 14 cm base disc, compress it with a rib and crosshatch the outer 2 cm.
- Roll coils 1.5 to 2 cm in diameter and no longer than 25 cm, resting them 10 minutes before use.
- Join each coil with a 45 degree diagonal weld, crosshatching both surfaces and applying slip.
- Blend each join inside and outside with a wooden tool, then cover the pot and stop for the day at about 8 cm.
- Wait 12 to 18 hours until a fingernail test at three heights gives a crisp white mark, then add three or four more coils.
- After every two coils, rib the wall inside and outside to a 6 mm thickness and the intended profile.
- Form the rim by rolling the top edge inward, compress it with a rib, and dry under loose plastic for five days.
- Punch two holes in the bag after 24 hours and remove the bag entirely after 72 hours.
Where it goes wrong
- Adding a coil to a wall that is not yet leather-hard. The pot slumps at the new coil line within 20 minutes.
- Alternating the joining direction between sessions. It leaves a helical line of weakness that opens in the firing.
- Rolling coils thinner than 1.5 cm. They dry too fast to blend and leave visible ridges.
- Unwrapping the pot for a look between sessions. The rim dries first and cracks before you get back to it.
| Symptom | Cause |
|---|---|
| Pot slumped at 22 cm | a coil was added to a wall that had not stiffened; check with the fingernail test at three heights. |
| Horizontal crack along a coil join after bisque | the join was blended on the outside only, leaving the inside unconsolidated. |
| Rim opened along the coil line | the rim was not compressed with a rib after forming. |
| Spiral crack running up the wall | joining direction alternated between sessions, creating a helical plane of weakness. |
Recipe and schedule numbers here were recorded on the workshop’s own kiln. A different kiln, a different thermocouple position or a different clay batch will move the result, so treat every firing schedule as a starting point and keep your own log beside it.