Drying Ceramic Pieces
Drying is the quiet stage between forming and firing, and the one most likely to ruin a piece without any obvious mistake. As water leaves the clay, the body shrinks. If one part of a pot dries faster than another, the two parts shrink by different amounts at the same moment, and the resulting stress shows up as a crack. Most of the craft of drying is simply making the process even and unhurried.
The stages of dryness
Potters describe drying using named states rather than exact moisture readings, because each state corresponds to what the clay will allow you to do.
| State | Feel | What it allows |
|---|---|---|
| Plastic | Soft, workable | Forming, joining, reshaping |
| Leather-hard | Firm but still cool and damp | Trimming, handles, carving, joining |
| Bone-dry | Dry, lighter, pale | Ready for the first firing |
Why uneven drying cracks pots
Thin areas such as rims and the edges of handles lose water quickly, while thick areas such as the base hold moisture longer. The thin parts shrink first and pull against the still-damp thick parts. Joins are especially vulnerable: a handle attached to a leather-hard body can shear off at the seam if it dries at a different rate than the wall it is fixed to.
In much of Canada, indoor winter air is very dry because of heating, which accelerates surface drying while cores stay damp. Many studios loosely tent fresh work with plastic in winter to slow the surface down. In humid summer conditions the opposite problem appears and pieces can take noticeably longer to reach bone-dry.
Slowing drying down
The common techniques all aim to even out the rate at which water leaves different parts of a piece.
- Cover loosely. Draping plastic over a piece traps humidity near the surface so it dries closer to the rate of the interior.
- Even exposure. Turning a pot occasionally and keeping it off direct heat or draughts prevents one side drying first.
- Protect extremities. Wrapping just the rim or handle areas slows the fastest-drying parts to match the body.
A piece is only ready for the kiln once it is genuinely bone-dry. Loading damp clay into a firing risks steam forming inside the wall faster than it can escape. That transition is covered in Firing and Kilns; the forming choices that set up even drying are discussed in Forming Clay on the Wheel.