How to diagnose pinholes in glaze before you waste another firing

Pinholes usually come from a small set of interacting causes: trapped gases, glaze application thickness, under-mature clay, or a firing/cooling curve that does not give the surface time to heal. Use this checklist to narrow the next test fast.

Fast triage checklist

1. Check whether the clay body or glaze is still off-gassing late in the firing.
2. Check whether the glaze layer is too thick on broad flat surfaces or rims.
3. Check whether bisque temperature left too much carbon or organics behind.
4. Check whether the glaze had time to smooth over before cooldown.

1. Gas release

If the body, glaze materials, or application water are still releasing gases late, the glaze surface can crater and freeze before healing. Try a cleaner bisque or a short hold near maturity.

2. Thickness

Pinholes often cluster where the coat runs heavier. Test one tile with a lighter dip or fewer coats before changing the whole recipe.

3. Cooling + soak

A short soak or slower finish can help a glaze heal. Confirm with a tiny kiln schedule variation before rewriting your base glaze.

Smallest useful confirmation test

Run two tiles with the same glaze and body: one lighter application, one current application. Keep everything else the same. If the lighter tile clears up, thickness is likely your first lever. If both still pinhole, test bisque cleanliness or a short maturity hold next.

When to use KilnPilot

If your issue mixes glaze chemistry, application, and kiln schedule, paste the exact recipe, clay body, firing curve, and failure notes into KilnPilot. It returns likely causes, what to change next, and the fastest confirmation test.