Glazes & testing 3 min read
Common Pottery Glazing Mistakes
An unexpected glaze result is easier to investigate when you know the clay, application and firing history. Start by describing the surface clearly. Several different problems can look similar in a photograph, and a single universal fix is unlikely to suit them all.
Skipping the test tile
A glaze sample made on another clay or fired in another kiln may not predict your result. Test on the clay body you actually use, with the same decoration underneath. Include the overlap if you intend to layer two glazes, and label which glaze went on first.
Keep a vertical test surface when checking movement, following your studio’s rules for protecting shelves. Do not make a favourite finished form the first test of an unfamiliar combination.
Applying an uneven or overly thick coat
Glaze can collect in grooves, around handles and at the bottom of a dipped piece. Record coat count or dip time and check these areas before firing. Follow the product guidance and studio procedure rather than assuming more glaze will produce a richer finish.
Keep the foot and the studio’s required clearance free of glaze. If a glaze runs, compare its application and firing history with your test tile before trying it again on functional work.
Treating crawling as only a dirty-pot problem
Crawling leaves exposed areas where the glaze has pulled away. Surface contamination can matter, but poor adhesion, excessive application thickness and cracking of the drying glaze layer can also contribute. Check the unfired coating for cracks or loose areas and record how the ware was prepared. Digitalfire’s crawling reference explains why several causes may need investigating.
Assuming pinholes just need more glaze
Small holes in the fired surface can involve gas release and a melt that did not heal before cooling. Clay, application and firing conditions all deserve attention. Adding another thick coat may introduce another variable without addressing the cause. Photograph the pits and compare a controlled test with your kiln operator. Digitalfire’s pinholing guide provides further background.
Confusing a crackle effect with a successful functional glaze
A network of fine cracks in a glaze is called crazing and commonly relates to the fit between glaze and clay. Record whether it appeared immediately or later. Do not assume an attractive surface or a recipe’s name establishes suitability for food contact; use the supplier’s guidance and appropriate testing for the finished clay-and-glaze combination.
Keep questionable pieces out of food use while you seek advice. A visual inspection alone cannot establish glaze durability or food-contact suitability.
Changing everything at once
If you switch clay, thin the glaze and change the firing in the same test, a better result will not tell you which change mattered. Keep a reference tile, change one factor where practical and record the result even when it is disappointing.
Finish each test note with a specific next step: “Compare the same glaze with one fewer coat”, for example. That turns a frustrating result into a question you can actually investigate.