Specialty Glaze Effects

Module 3: Specialty Glaze Effects

1. Creating Textured Finishes

Textured glazes add tactile and visual depth, transforming surfaces with organic, unpredictable effects.

A. Intentional Glaze Defects for Texture

• Crawling Glazes:

• What Happens: Glaze pulls apart, revealing bare clay beneath.

• How to Achieve:

• Apply glaze too thickly.

• Use high-shrinkage ingredients (e.g., high alumina or excessive flux).

• Artistic Use: Cracked lava or reptilian skin effects.

• Crater Glazes:

• What Happens: Bubbles burst during firing, leaving pitted craters.

• How to Achieve:

• Add gas-producing materials (e.g., carbonates, organics).

• Fast firing traps bubbles before they smooth out.

• Artistic Use: Moon-like surfaces or "volcanic" textures.

• Crystalline Glazes:

• What Happens: Zinc or titanium promotes crystal growth in cooling glaze.

• How to Achieve:

• Slow-cool kiln cycle (1100°C–900°C) for crystal formation.

• High zinc oxide content (20–30%).

• Artistic Use: Sparkling floral or snowflake patterns.

B. Additives for Enhanced Texture

• Sand/Grog:

• Mixed into glaze for gritty, matte finishes.

• Tip: Use fine mesh (80–120 grit) to avoid sharp edges.

• Silica/Silicon Carbide:

• Creates micro-bubbles or "orange peel" texture.

• Fibers (e.g., paper, horsehair):

• Burn out during firing, leaving delicate trails.

2. Reduction & Oxidation Firing Effects

The kiln atmosphere dramatically alters glaze chemistry and color.

A. Reduction Firing (Oxygen-Starved)

• Process: Fuel-burning kilns (e.g., gas, wood) limit oxygen, forcing glazes to "steal" it from metal oxides.

• Key Effects:

• Copper Reds:

• Copper oxide turns blood-red (e.g., traditional Chinese Jun glaze).

• Requires heavy reduction at ~1300°C.

• Celadons:

• Iron oxide transforms into soft blue-greens (e.g., classic Korean celadon).

• Reduction enhances translucency.

• Metallic Lusters:

• Iron and cobalt develop metallic sheens (e.g., temmoku blacks).

B. Oxidation Firing (Oxygen-Rich)

• Process: Electric kilns maintain neutral/oxidized atmosphere.

• Key Effects:

• Bright, Stable Colors:

• Cobalt stays true blue; iron yields warm browns/yellows.

• No Reduction Effects:

• Copper remains green (not red); celadons appear more opaque.

Comparison Table:

Workshop Activity:

1. Test Tiles:

• Fire identical glazes in oxidation vs. reduction to compare.

2. Texture Experiment:

• Apply a crater glaze to one tile, crystalline to another.

Safety Note:

• Crystalline glazes often run—use stilted shelves to catch drips.