The Join Is the Most Critical Moment
Adding a coil to a leather-hard section sounds simple, but the join must be invisible and structurally sound. A poorly joined section will crack during drying or crack in the bisque firing.
Preparing the Rim
Before adding a coil, score the top rim of the base section with a serrated rib or needle tool. Apply a thin coat of slip. The slip acts as glue: it fills the porous surface and helps the new wet clay bond to the firm clay beneath.
Laying and Blending the Coil
- Roll a thick, even coil slightly longer than the circumference of the rim.
- Press it gently onto the scored, slipped rim.
- Blend the inside of the join first, using your finger or a small wooden tool to press the coil down and inward into the existing wall.
- Then blend the outside.
Throwing the New Section
Once the coil is blended, the wheel goes on and you throw the new clay upward just as you would any wall. The coil becomes the raw material for the next section of wall.
- Work gently: the base is leather hard and does not flex. Rough handling can crack the join.
- Compress the new walls lightly as you pull them up.
- Stop before the new clay gets floppy. Let it firm up before adding another coil if needed.
The Final Surface
After all sections are added and the pot has stiffened to leather hard, use a metal rib to scrape and unify the outside surface. This removes the subtle ridges at each join and gives the pot a single, continuous silhouette.
Dig Deeper
The coil-and-throw method is closely related to the ancient coil-building techniques used in cultures worldwide long before the potter's wheel existed. Understanding how vitrification bonds clay particles during firing helps explain why a well-blended join becomes invisible and structurally sound in the finished piece. Many contemporary studio pottery artists use sectional throwing to create large-scale work that pushes the limits of the wheel.
Common Mistakes and Quick Fixes
- Light scoring with poor key: Use clear texture and enough slip for a full bond.
- Blending outside first only: Blend inside join first, then outside for strength.
- Overpulling fresh section: Stop before walls get floppy and let clay set up again.
- Leaving join ridges unresolved: Rib the exterior at leather hard for a unified silhouette.
Practice Exercise
Build a two-section vessel and intentionally over-document the join: photos at scoring, slipping, blending, and post-rib finish. Review after bisque and glaze. This creates a repeatable join protocol you can trust on larger work.
