Glazing & Firing
Making the pot is only half the process. Drying, bisque firing, glazing, and the final glaze firing turn soft clay into permanent ceramic. Understanding each stage prevents the most common heartbreaks.
1. Drying
Clay must dry slowly and evenly. Fast drying causes cracks, especially in thick sections or at joins.
- Cover work loosely with plastic for the first day or two
- Then uncover gradually or leave under a light cloth
- Thick pieces and sculpture may need days to weeks
- Bone dry = room temperature, no cool feeling to the touch, lighter in color
Never put damp clay in a kiln. Water turns to steam and can explode the piece (and damage neighboring work).
2. Bisque Firing
The first firing. It drives out remaining chemical water and organic matter and turns the clay into a hard but still porous ceramic (bisque). Typical range for beginners is cone 06–04 (low) or sometimes higher depending on the clay and studio practice.
- Pieces can touch each other in the bisque load (unlike glaze loads)
- Bisque is easier to handle and absorb glaze
- Still fragile compared with fully vitrified ware
3. Glazing Basics
Glaze is a glass-forming mixture suspended in water. When fired to the right temperature it melts, flows, and hardens into a durable, often colorful surface.
Common application methods
- Dipping — Fast and even. Requires a bucket of glaze and tongs or a dipping setup.
- Pouring — Good for insides of pots and controlled coverage.
- Brushing — Flexible for detail and small batches. Use glaze specifically formulated for brushing (or add a brushing medium).
- Spraying — Even coats and gradients, but needs a spray booth and respirator.
Critical beginner rules
- Wipe the bottom (foot) clean of all glaze — glaze melts and will glue your pot to the kiln shelf
- Match the glaze’s firing range to the clay and the kiln schedule
- Test new glazes on small tiles or sacrificial pots first
- Keep glaze off kiln furniture and from dripping onto other work
4. Glaze Firing
The second firing. Temperature is chosen to mature both the clay body and the glaze. Stoneware is commonly fired to cone 5–6 or cone 10; earthenware lower.
In the kiln, glaze becomes molten glass. Pieces must not touch. Kiln stilts or carefully placed supports are used for certain forms. Cooling is also controlled — rapid cooling can crack pieces or cause glaze defects.
Common Glaze Problems & Causes
| Problem | Likely Causes |
|---|---|
| Crawling (glaze pulls away) | Dusty bisque, thick application, grease on surface |
| Pinholing / blistering | Gases escaping, thick glaze, underfired or too rapid |
| Crazing (fine cracks) | Glaze contracts more than clay on cooling |
| Shivering (glaze flakes off) | Clay contracts more than glaze |
| Running onto shelf | Too much glaze, overfired, or glaze too fluid |
Most of these are diagnosed with experience and by keeping notes of what you applied and how the kiln was fired.
Safety Notes
- Many glaze materials are toxic in raw form — avoid inhaling dry glaze dust; use a respirator when mixing or spraying
- Never eat or drink around raw glazes
- Wash hands thoroughly after handling
- Ensure kilns are properly ventilated; never fire in a living space without correct extraction