Why Did My Glaze Run? Fixing Drips and Stuck Pots

A glaze that runs is a glaze that moved. It melted, flowed down the pot and pooled at the bottom, or worse, slid onto the kiln shelf and fused your pot to it. It is one of the most common and most expensive glaze mistakes.

Here is why it happens and how to stop it.

The main causes

Too much glaze. A thick coat has more liquid to flow. This is the number one reason, especially with layered glazes. Our guide on how many coats of glaze helps you judge thickness.

Too much heat. Firing beyond the glaze's cone makes it more fluid. If the kiln overshoots, glazes that behaved last time may run. Check against the cone chart.

A fluid glaze by nature. Some glazes, especially shiny, glassy ones and many glazes with high flux, are runny even at the right thickness. Test them on a tile.

Layering. Two glazes that behave on their own can run together because their combined melting point is lower.

Glaze too close to the foot. Any glaze on the bottom edge can flow onto the shelf.

Prevention checklist

1. Leave the foot bare. Keep glaze about 3 to 5 mm (1/8 to 1/4 in) above the bottom edge and wipe the foot clean with a damp sponge.
2. Apply thinner. Especially on the lower third of the pot, where glaze collects.
3. Test combinations on a tile set at a steep angle.
4. Use kiln wash on your shelves so a drip can be chipped off. Read about kiln wash.
5. Place a cookie. A small fired clay disc under a risky pot catches a drip and protects the shelf.
6. Give pots space. See why clearance is everything.
7. Fire to the right cone. Do not push a firing hotter hoping for a better result.

If a pot fused to the shelf

Don't pull. You will break the pot, the shelf or both. Instead:

1. Let the kiln cool fully.
2. Assess: is the pot still attached, or has it bonded to the shelf?
3. Put on safety glasses and a respirator rated for fine dust. Grinding glass and ceramic makes harmful dust.
4. Lightly chip or grind the glaze around the foot, working to free the pot.
5. Use a hand grinder or diamond pad with water when possible to keep dust down.
6. Smooth the foot of the pot, and grind the drip off the shelf until flat.
7. Re-apply kiln wash to the shelf.

For a full walkthrough, see grinding drips off a kiln shelf. If the studio owns the kiln, tell the studio manager. Do not try to fix a shelf alone.

Is the pot ruined?

Often not. If the glaze ran down but did not fuse, the pot is fine. You can grind the foot smooth and refire if needed. A pot with a pooled bottom may be fine for decoration but not for food, as it can be rough or uneven.

Keep a firing log

Run problems often repeat with the same glaze. Write down what you applied and where it ran, so next time you can thin the coat or choose a different combination. In Claybook, glaze and layering notes live with the piece.

For other fired-glaze faults, see our glaze defect guide.