“The Journey of Stoneware Clay in a Cone 6 Kiln”

Charts Below

 In ceramics and material science, many of the stages in a firing cycle do have scientific names that describe the transformations in the clay minerals and other materials. Here’s a refined version of the cone 6 stoneware stages with their more technical terms:

So, in summary, the main scientific terms are:

• Dehydration (free water loss)

• Dehydroxylation (chemically bound water loss)

• Oxidation (burning off organics)

• Polymorphic inversion (quartz / cristobalite)

• Metakaolinite formation

• Spinel phase

• Mullite formation

• Vitrification

1. Drying / Dehydration

Temp: Room temp → 212°F (100°C)

• Scientific term: Drying (free water evaporation)

• Physical process only – removal of unbound water from pores.

2. Dehydroxylation

Temp: 212–840°F (100–450°C)

• Scientific term: Dehydroxylation

• Chemically bound water (hydroxyl groups) is driven off from clay minerals (esp. kaolinite).

3. Oxidation / Combustion

Temp: ~750–1050°F (400–565°C)

• Scientific term: Oxidation reactions

• Organic materials, carbon, and sulfur compounds oxidize.

4. Quartz (Cristobalite) Inversion

Temp: 1063°F (573°C) (for quartz)

• Scientific term: Polymorphic inversion

• Quartz changes from α-quartz (low) to β-quartz (high), expanding ~2%.

• Cristobalite inversion can also occur later if present.

5. Metakaolin Formation

Temp: ~930–1470°F (500–800°C)

• Scientific term: Decomposition of kaolinite → metakaolinite

• Structure collapses, leaving amorphous alumino-silicate.

6. Spinel Phase Formation

Temp: ~1830–2010°F (1000–1100°C)

• Scientific term: Spinel-type phase formation

• Metakaolinite transforms further, forming transitional phases before mullite.

7. Mullite Formation & Vitrification

Temp: ~1830°F – Cone 6 (1222°C)

• Scientific terms:

  • Mullitization → growth of mullite crystals (3Al₂O₃·2SiO₂).

  • Vitrification → partial melting of fluxes (feldspar, etc.), creating a glassy matrix that locks the mullite needles and un-melted quartz in place.

• This is what makes stoneware dense and strong.

8. Cooling & Polymorphic Inversions

Temp: Down through 1063°F (573°C)

• Scientific term: β-quartz → α-quartz inversion

• Must be slow to avoid thermal shock (dunting).

• Cristobalite inversion can also occur ~439°F (226°C) if cristobalite formed in the body.