You have thrown, trimmed and bisqued a pot you are pleased with. Then the glaze goes on, the kiln fires, and it comes out with a pinhole in the middle of the rim or a bald patch where the glaze has retreated like a puddle on a greasy plate. Most glaze faults are not mysterious. They come from a small number of habits, and once you can read the signs, they are usually straightforward to fix. Here are ten common mistakes, grouped by the problems they cause, with practical changes you can make in your next glazing session.

Mistakes 1 and 2: pinholes, dust and the wrong bisque

Pinholes are small craters, often with a tiny speck at the bottom. They form when gas escapes through a glaze that has already sealed over. The gas comes from somewhere: organic matter in the clay, carbonates in the glaze, air trapped in a thick layer, or water and dust on the surface. The first mistake is applying glaze too thickly. A layer roughly the thickness of a credit card is usually enough. If the surface looks like a coat of icing, it is too heavy, and the glaze will trap bubbles instead of letting them rise.

The second mistake is glazing dusty or greasy bisque. Fingers, kiln wash and workshop dust all stop the glaze from gripping. Wipe the pot with a damp sponge and let it dry before dipping. Other useful fixes: bisque slowly with a soak at the top of the cycle to burn out carbon; sieve your glaze before use; and if pinholes persist, try a drop-and-hold firing, or slow the cooling so bubbles have time to heal. Change one thing at a time, and test it on a tile rather than on a finished piece.

Mistake 3: letting glaze crawl

Crawling looks like the glaze has pulled back into islands, leaving bare clay between them. It usually comes from glaze applied too thickly, especially in several wet coats; from a dusty or oily surface; or from a glaze that shrinks a great deal as it dries. The fix is rarely dramatic. Thin the glaze, apply fewer and thinner coats, clean the bisque properly, and avoid handling pots with lotiony hands. A very small addition of a binder such as gum arabic can improve adhesion, but test it first: too much can make crawling worse. On complex forms, pour the glaze rather than dipping, and drain the corners so glaze does not pool there.

Mistake 4: ignoring shivering

Shivering is when flakes of glaze lift away from the pot, often at rims, edges and feet, leaving sharp slivers of bare clay. It is a glaze-fit problem, not a surface problem. The glaze is under compression because the body contracts more than the glaze does on cooling. Applying glaze more thinly will not solve it. You need to adjust the recipe or change the clay body so the two move together. Make a test tile with the same body and glaze, fire it, and check the fit before committing a batch. Shivered edges can be razor-sharp, so handle suspect pots with care and do not sell them as food-safe until the fit is corrected.

Mistakes 5 and 6: uneven coverage

The fifth mistake is dipping by eye. Glaze thickness matters, and the easiest way to control it is to control the glaze itself. For many dipping glazes, a specific gravity of around 1.4 to 1.5 is a useful starting range, though your recipe may differ. Too thin and the surface goes patchy; too thick and it runs, crawls or blisters. The sixth mistake is failing to keep the glaze in suspension. Some glazes settle hard, and a little Epsom salts solution can help flocculate them, but overdo it and you get a gel. Stir before every dip and use the same motion each time.

  • Measure specific gravity with a glaze hydrometer, and note it in your records.
  • Dip once, let the glaze dry to a matte finish, then dip the second area with a clean overlap.
  • Use tongs with even pressure, or pour large pieces to avoid finger marks.
  • Wax the foot and any areas where glaze should not go.
  • Scratch a line through the dry glaze with a pin: aim for an even, opaque line, not a transparent one.

Mistakes 7 and 8: firing and cooling

The seventh mistake is firing too fast. Glazes need time to melt, smooth out and release their gases. A fast climb can leave pinholes, blisters and dull surfaces. The eighth mistake is ignoring the cooling cycle. Rapid cooling can cause crazing, dunting and poor glaze development. A controlled cool, or a soak at the end of the firing, often gives a noticeably better surface. Use cones as well as the controller, and keep shelves clean: kiln wash dust falling onto pots is a common cause of speckled, rough patches. Glaze materials can be hazardous in dust form, so wear a suitable mask when mixing and keep food well away from the studio.

Mistakes 9 and 10: contamination and poor records

Contamination is quiet and persistent. A dirty tool, a brush used for two different glazes, or rinse water tipped into the wrong bucket can change a glaze for good. Keep one bucket per glaze, label everything clearly, and store mixed glazes with their recipe and date. The tenth mistake is not keeping records. Note the clay body, glaze name, specific gravity, number of dips, firing schedule, cone and result. Add a photograph and keep a fired test tile. Without records you cannot repeat a good result, and you cannot work out why a bad one happened.

A practical routine that prevents most faults

Good glazing is mostly a matter of order and observation. Try this sequence for your next batch:

  1. Wipe the bisque with a damp sponge and let it dry completely.
  2. Stir, sieve and check the specific gravity of every glaze.
  3. Apply thin, even coats, and write down what you did.
  4. Fire with cones, and plan a soak or a slower cool.
  5. Test on the same clay body before glazing a large batch.

None of this removes the need for test tiles, but it does make faults easier to diagnose. When something goes wrong, look at the pot, check your notes and change one variable. Glazing rewards patience far more than luck.

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