The drying process must be carefully controlled as an essential step between molding clay and firing finished ceramic pieces. Air and kiln drying can introduce stresses like shrinkage that manifest as cracks, fractures, and deformation.
However, with attentive air drying habits and control of kiln moisture, you can successfully transition clay work through the delicate drying stage without mishaps. Here are tips for flawless clay drying from start to finish:
The key to crack-free drying starts before clay even leaves the worktable. Only use smooth, consistent, well-conditioned clay that has:
Properly prepared clay with even moisture distribution and density will dry smoothly.
Never rush or force the air drying process. Both sudden drying and overly slow drying cause issues. Maintain a controlled, gradual pace.
Set pieces to dry in a climate-controlled room at around 70°F. Avoid direct sun, heaters, or drafts that desiccate the surface too quickly. Drape plastic wrap or damp cloths loosely over work if drying too fast.
Turn pieces regularly as they dry to prevent uneven stresses. Consider investing in a humidifier to add moisture back if needed in very dry conditions.
Learn to recognize the range of material states clay passes through as it dries:
Leather hard is ideal for smoothing surfaces and finishing details before bisque firing. If clay gets overly dry, re-wet by spraying or sealing in plastic.
As clay loses moisture, shrinkage stresses develop within the material. Notice these warning signs:
Take corrective action if observing these issues by adjusting humidity or supports.
While forms require support during drying, improper supports themselves can introduce cracking:
Support fully from below to prevent distorting forces.
The final stage of drying happens in the bisque kiln. Rapid heating or cooling risks shocking clay.
Program kiln with gradual ramp rates between 60-120°F per hour. Pause at 180°F to allow heat to equalize before slowly proceeding.
Try bisque firing protective saggars or beds of alumina sand that insulate pieces from temperature spikes.
Shrinkage tears clay apart when thickness varies within a piece. Maintain as uniform a wall profile or slab thickness as possible without abrupt transitions that concentrate stresses.
Avoid pinched areas, heavy joining points with other sections, and pointed protrusions or handles. Design flowing, gradual contours.
For unavoidable clay thickness changes like spouts and handles, add reinforcements:
This eases the transition in rigidity, so stresses stay distributed.
Always bisque fire clay pieces to completion before applying glazes or decorations. Firing a wet glazed piece is virtually guaranteed to fail due to the added moisture.
Drying clay fully to bisque stage removes nearly all moisture and shrinkage tendencies before risking decorative surface applications.
You can minimize frustrating cracks and warp with mindful preparation, drying, and firing practices. Be attentive, control the environment, and respond promptly to any issues. A bit of patience ensures your clay work survives intact to final firing.