Fix a crazing issue

Crazing is the most common glaze fault, and one of the most fixable once you understand the chemistry.

Background

Crazing happens when the glaze shrinks more than the clay body during cooling. The glaze is under tension, so it cracks.

The fix (simplified)

Increase silica slightly in the glaze recipe (silica raises the thermal expansion coefficient of the glaze to match the clay). Or decrease flux (fluxes lower expansion).

The experiment

1. Start with a glaze recipe that crazes on your clay body
2. Make a small batch with 2–3% more silica (or 2% less flux)
3. Apply to a test tile
4. Fire and compare to the original

Assessment

• No crazing = problem solved. Document the new recipe.
• Less crazing = right direction, adjust further
• Same crazing = try a different adjustment (maybe reduce feldspar instead)

The reality

Glaze chemistry is iterative. Expect 2–3 rounds of testing before you solve a crazing problem completely.