You finished your first pottery mug. You filled it with coffee. Twenty minutes later, the saucer was soaked. What happened?
Leaking pottery is the most common beginner problem, and the fix is usually one of three things.
Reason 1: Wall Thickness Issues
If you threw a mug with super thin walls or uneven thickness, the bottom may be too thin in spots. Combined with the porous nature of unfired clay, this creates pinholes after firing.
The fix: aim for walls about 1/4 inch thick at the bottom and 1/8 inch at the rim. Use a needle tool to check thickness while throwing.
Reason 2: Wrong Clay Body
Different clays vitrify (become non-porous) at different temperatures. If you used earthenware clay and fired it to bisque only — common in many beginner studios — the body is still porous. Water seeps through the glaze and gets absorbed by the clay underneath.
The fix: use stoneware fired to cone 6 or cone 10. Stoneware vitrifies fully at those temperatures. Earthenware can be glazed waterproof but requires specific glazes that fit the body.
Reason 3: Crawling or Pinhole Glaze
If your glaze pulled back from the surface during firing (called "crawling") or developed tiny holes ("pinholing"), water can seep through the gaps in the glaze coating.
The fix: apply glaze evenly, ensure proper thickness (about 1/16 inch), and avoid touching the glaze surface before firing. Glazing technique matters more than glaze choice.
Diagnosing Your Mug
Fill the mug with water and let it sit for 30 minutes. Then:
- Drips from the bottom: wall thickness or clay body issue
- Outside feels damp all around: porous clay body, glaze isn't sealing
- Specific wet spots: pinholes in the glaze
Fixing an Existing Leaky Mug
If you have a piece you love that leaks, you can re-glaze and re-fire it. Some studios charge for re-fires, others include it. A second glaze layer often seals the issue.
Better From the Start
At our studio, we'll teach proper wall thickness on the wheel and use stoneware that vitrifies fully at our firing temperatures. Wheel throwing classes include this material education from day one. Join the waitlist for opening updates.
Join the Charlotte Pottery Community
Charlotte Pottery Studio is opening in 2026. Sign up for our waitlist to get founding member pricing, priority class registration, and studio updates.