Two Glazes Are Better Than One
One of the most rewarding discoveries in glazing is that overlapping two different glazes produces a third: an emergent color and surface quality that neither glaze has on its own. This is where glazing becomes genuinely creative.
Why Glazes Interact
In the kiln, glazes melt and flow. Where two glazes overlap, their chemistries mix at the boundary. The result can be:
- A new intermediate color (cobalt blue over iron amber can produce a rich teal-green).
- Texture (a matte glaze under a glossy one can produce a broken, crystalline surface).
- Depth (the overlap zone looks deeper and more complex than either glaze alone).
Controlled Overlapping
The most common technique: dip the pot in a base glaze, let it dry, then brush, pour, or dip one end in a second glaze. The overlap zone is where the two meet.
- Aim for an overlap band of 3–5cm for best visual effect.
- Apply the second glaze deliberately: a clean, decisive edge looks more intentional than a ragged one.
The Running Risk
Overlapping glazes are thicker where they meet. Both glazes melt and can flow. If the pot is not properly prepared (waxed foot, clean base), a double-thickness overlap zone can run all the way to the kiln shelf.
Rule: Wherever you have two glaze layers, keep the overlap high on the pot, at least 3–4cm from the base. Glaze always runs downward.
Testing Combinations
Every glaze behaves differently from every other. Before committing a combination to a finished piece:
- Apply both glazes to a test tile in an overlapping band.
- Fire the test tile.
- Only then decide whether to use the combination on real work.
Overlap Safety Checklist
Before loading overlapped work:
- Overlap band is well above foot (3–4cm minimum)
- No obvious thick drips in the overlap zone
- Foot and bottom centimetre are completely clean
These checks keep adventurous layering from turning into shelf damage.
Pro Tip
Keep a glaze test journal: a notebook with test tile results, glaze names, combination notes, and cone numbers. Over time it becomes your most valuable studio reference.
The Bigger Picture
The way overlapping glazes interact in the kiln is governed by the same chemistry described in the Wikipedia article on ceramic glaze, where different flux materials determine melting point and flow. Potters use pyrometric cones to verify that test tiles and finished pieces reach the exact temperature needed for their glaze combinations to mature properly.
Common Mistakes and Quick Fixes
- Placing overlap too low: Keep overlap bands high to reduce shelf-risk runs.
- Skipping test tiles for new combos: Fire a tile first, always.
- Overlapping too thickly on first try: Start narrow and increase coverage in later tests.
- No tracking system: Record glaze names, cone, overlap width, and results every time.
Practice Exercise
Create a mini matrix with one base glaze and three top glazes, each at two overlap widths. Fire and label all tiles. This turns layering from guesswork into a reliable design tool.
