Terra Sigillata - Adding Colorants

Adding oxides to terra sigillata is a delicate way to infuse the surface with subtle, earthy color while preserving its smooth, reflective quality.

Because oxides are finely ground minerals, they integrate naturally with the clay rather than sitting on top like a paint, making them ideal for burnishing and sgraffito.

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For 10 oz:

Red Iron Oxide : 0.3 to 2 percent

0.9 g → soft blush, warm clay skin

1.8 g → classic iron earth

5.7 g → deep red brown, sheen begins to soften

Yellow Iron Oxide: 0.5 to 3 percent

1.4 g → pale ochre

2.8 g → honey, sun baked earth

8.5 g → heavy ochre, reduced sheen

Black Iron Oxide: 0.1 to 1 percent

0.3 g → smoky gray

0.6 g → charcoal brown

2.8 g → very dark, sheen loss risk

Manganese Dioxide : 0.1 to 1 percent

0.3 g → violet brown haze

0.6 g → umber, soft shadow

2.8 g → matte, brittle edge risk

Copper Carbonate : 0.1 to 1 percent

0.3 g → pale green wash

0.6 g → sea green

2.8 g → fluxing risk, crawling possible

Chrome Oxide : 0.1 to 0.5 percent

0.3 g → lichen, gray green

0.6 g → olive moss

1.4 g → forest green, sheen danger

Important material notes (especially for sgraffito):

• Always pre slake oxides into a slurry

• Strain when possible

• Apply thin layers only

• Too much color causes flaking when carved

  

Steps for Pre-Slaking Oxides

1. Measure Carefully

• Weigh your oxide

2. Add Water Slowly

• Use just enough water to turn the oxide into a thin slurry, like heavy cream or melted honey.

• Too much water is okay; you can adjust by evaporation or gentle stirring, but too little makes lumps.

3. Mix Thoroughly

• Stir with a small spatula, palette knife, or mini whisk until all particles are suspended.

The goal: no clumps, no specks, fully dispersed.

4. Strain (Optional )

• Use a fine mesh strainer (100–200 mesh) to remove any stubborn clumps.

• This ensures a uniform, even layer when applied.

5. Combine With Terra Sigillata

• Slowly fold the slurry into your pre-mixed sigillata.

• Stir gently until fully incorporated. Avoid whipping air into the surface.

  
  

The amounts listed here are intended as working ranges, not absolutes. Clay bodies, firing temperatures, and atmospheres will all influence the final surface. Test small batches, apply thin layers, and adjust gradually. Terra sigillata rewards patience and close observation.

Across cultures and centuries, surface treatment has been a dialogue between earth and hand. Adding colorants to terra sigillata continues this lineage. By working slowly, layering lightly, and revealing through subtraction, the surface becomes more than finish. It becomes record.