High-fire clay bodies are formulated to withstand extreme kiln temperatures — typically cone 8 through cone 10 (approximately 2300–2380°F / 1260–1305°C). At these temperatures, clay bodies vitrify significantly, producing ware that is dense, durable, and often translucent in the case of porcelain. High-fire ceramics are prized for their strength, subtlety, and the dramatic atmospheric effects possible in reduction firing.
What Makes a Clay Body High Fire?
High-fire clay bodies contain higher percentages of refractory materials — primarily kaolin and silica — that allow them to withstand extreme heat without deforming. They also contain feldspar, which acts as a flux at high temperatures, promoting vitrification. Common high-fire clay types include:
High-fire stoneware — dense, strong, and typically grey or buff in color. Works well in both oxidation and reduction. Excellent for functional ware.
High-fire porcelain — white, translucent when thin, and fully vitrified at cone 10. More challenging to throw and hand build due to its lack of plasticity, but produces refined, elegant results.
Grolleg porcelain — uses Grolleg kaolin (English china clay) for exceptional whiteness and translucency. Highly regarded for slipcasting and fine throwing work.
High Fire Clay Body Recipe (Cone 10)
This is the University of the Arts cone 10 porcelain-style clay body — a clean, white, throwable body with good vitrification at cone 10. The high Grolleg content gives excellent whiteness and translucency.
Material
Percentage
Custer Feldspar
23%
Grolleg (English Kaolin)
55%
Silica (Flint)
22%
Bentonite or Macaloid (addition)
1%
The bentonite or macaloid addition improves plasticity — essential for a Grolleg-heavy body which can otherwise be stiff and difficult to throw.
Working with High Fire Clay
Throwing
High-fire porcelain bodies are less forgiving on the wheel than stoneware. They have less plasticity, meaning they fatigue faster and are more prone to cracking if overworked. Keep your sessions short, work efficiently, and avoid adding too much water. Use a rib to compress and refine rather than relying on your hands alone.
Drying
High-fire porcelain dries unevenly if not managed carefully. Cover pieces loosely with plastic and rotate them regularly to ensure even drying. Rims and thin areas dry faster than bases — slow drying prevents cracking.
Firing
High-fire clay bodies have a narrower firing window than mid-fire. Fire too low and the clay won’t vitrify; fire too high and pieces will bloat, warp, or slump. Always use witness cones alongside your kiln’s thermocouple to verify actual heat work, not just temperature.
High Fire vs Mid Fire
Many potters work at cone 6 (mid-fire) rather than cone 10 because modern cone 6 glazes have improved dramatically and the lower temperatures are easier on kilns and more energy efficient. However, high fire offers advantages that mid-fire can’t replicate — particularly in reduction firing, where the atmosphere in the kiln chemically interacts with iron and other colorants to produce effects impossible in oxidation.
I am a visually impaired ceramic artist. I have been making for around 8 years now. I specialize in functional colorful pottery. Mainly nerikome and other decorative processes.
