Glaze Chemistry Basics — Simplified
Every pottery glaze is built from three types of ingredients working together. Understanding this trio lets you read any recipe and predict how it will behave in the kiln.
- Silica (SiO2) — the glass former. This is what creates the smooth, glassy surface. Too much and the glaze won't melt; too little and it runs off the pot.
- Alumina (Al2O3) — the stiffener. Alumina keeps the melted glaze from flowing down the sides of your pot. It comes primarily from clay and feldspar.
- Flux — the melting agent. Fluxes like feldspar, whiting (calcium carbonate), and talc lower the melting point so your glaze matures at kiln temperatures.
Master potter Stephen Jepson, with over six decades of experience, teaches that glazing is where science meets art. Understanding these basics transforms glazing from guesswork into confident, repeatable results.
4 Reliable Glaze Recipes
1. Clear Gloss Glaze
The essential base glaze every potter needs. Transparent, glossy, and food-safe. Use alone to show off clay color, or add colorants for custom colors.
Recipe: Custer Feldspar 25%, Silica 25%, EPK Kaolin 15%, Whiting 20%, Talc 10%, Wollastonite 5%. Add 2% Bentonite for suspension.
Tip: Add 1–3% Mason stains to this base for reliable colored glazes. Cobalt carbonate at 0.5% gives a beautiful blue.
2. Celadon Glaze
A classic jade-green glaze prized in Asian ceramics. The green comes from a small amount of iron oxide reduced in a gas kiln — or approximated in electric kilns with the right chemistry.
Recipe: Custer Feldspar 40%, Silica 20%, Whiting 20%, EPK Kaolin 10%, Talc 10%. Add 1.5% Red Iron Oxide and 0.5% Tin Oxide.
Tip: Apply thick for deeper color. Pools beautifully in carved textures and stamped impressions.
3. Tenmoku Glaze
A rich, dark brown-black glaze with amber highlights where it thins over edges. One of the most dramatic stoneware glazes, originating from Chinese Jian ware.
Recipe: Custer Feldspar 45%, Silica 15%, Whiting 15%, EPK Kaolin 10%, Talc 5%, Ball Clay 10%. Add 9% Red Iron Oxide.
Tip: The magic of tenmoku is how it breaks over texture. Carved and faceted forms show the best contrast between the dark body and amber edges.
4. Matte White Glaze
A smooth, satiny white that works beautifully on functional ware. Non-glossy finishes are trending in ceramics and feel wonderful in the hand.
Recipe: Nepheline Syenite 30%, Silica 25%, Whiting 15%, EPK Kaolin 15%, Zinc Oxide 10%, Barium Carbonate 5%. Note: barium is toxic — handle dry materials with a respirator.
Tip: Layer under other glazes for interesting interaction effects. Matte white under tenmoku creates beautiful movement.
Application Techniques
Dipping
The fastest and most consistent method. Hold bisqueware with tongs, submerge for 2–3 seconds, and pull out smoothly. Best for even coverage on simple forms. Mix your glaze to heavy cream consistency.
Pouring
Ideal for the inside of bowls and vases. Pour glaze in, swirl to coat, and pour out. Then pour over the outside while holding the piece upside down. Works well when you don't have enough glaze volume for dipping.
Brushing
Most common for hobbyists. Use a soft, wide brush and apply 3 thin coats, alternating brush direction. Allow each coat to dry before applying the next. Brushed glazes tend to show brush marks — which can be a desirable texture.
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