The most common mistake with celadon is adding more iron to get a deeper green. It does not work. Celadon colour is a function of how much light travels through the glaze before it reflects back, so a thick layer of a 1.5 percent iron glaze is far greener than a thin layer of a 3 percent one — and the 3 percent version goes olive and muddy instead. This recipe is built around that fact.
H 15 · Ø12 / Ø14 / Ø5.5 cm
Base
A high-calcium, low-iron celadon for cone 10 reduction on porcelain. The colour comes from about 1.5 percent iron oxide dissolved in a lime-rich glass, and the depth comes from the thickness of the glaze rather than from the amount of iron.
| Material | Parts | Share |
|---|---|---|
| Custer Feldspar | 30 | 29.6% |
| Silica (SiO₂) | 22 | 21.7% |
| Whiting (CaCO₃) | 20 | 19.7% |
| EPK Kaolin | 14 | 13.8% |
| Dolomite | 8 | 7.9% |
| Barium Carbonate (BaCO₃) | 6 | 5.9% |
| Red Iron Oxide (Fe₂O₃) | 1.5 | 1.5% |
| Total charge | 101.5 |
Fired surface
A pale blue-green that ranges from a near-white celadon on a thin application to a deep sea-green where the glaze pools at the foot. Where the glaze is thickest over carved decoration, the colour deepens and the carving reads clearly through the glass.
Chemistry: lime, iron and reduction
In an oxidised firing, 1.5 percent iron in a lime glaze gives a pale yellow-green or a beige. In reduction, some of the iron converts from the ferric to the ferrous state, and ferrous iron in a calcium-rich glass gives the blue-green of classic celadon. That conversion happens between 900 and 1100 degrees Celsius, which is why reduction needs to be established early and held through the middle of the firing.
The calcium is as important as the iron. Whiting and dolomite together make up 28 percent of this recipe, and they are what produce the blue cast. Barium carbonate at 6 percent matte-s the surface slightly and stabilises the colour against small variations in the firing.
Reduction schedule
Start reduction at 900 degrees. With a gas kiln, close the damper partway and reduce the primary air until the flame is about 30 cm long at the burner ports and there is a visible orange flame at the flue. Hold light reduction from 900 to 1200 degrees, then increase to medium reduction — flame to about 60 cm — through the body of the firing from 1200 to cone 10.
Heavy reduction all the way through will give a grey, opaque celadon; oxidation after 1200 will give a yellow-green. Body reduction from 1200 to 1260 is what produces the depth, and there is no substitute for a pyrometer and a notebook here. Record air settings, damper position and the flue flame at every 50 degrees.
Application: thick, even, and on the right body
Apply celadon at 0.8 to 1.2 mm. Thin celadon is a waste of the glaze: at 0.4 mm the same recipe reads as a pale grey-white with only a hint of green. Pour the inside and dip the outside, or dip twice with a short dry in between, and always work on a porcelain body — a stoneware with 2 percent iron will fight the glaze and give a dirty green at the edges.
Carved or incised decoration needs a slightly thicker application, because the glaze thins over the raised lines and thickens in the cut. That is exactly the effect that makes celadon the traditional partner of carved porcelain: the pattern appears not from colour but from depth.
Reading the results
A correct celadon has a slight translucency — you should be able to sense the carved line through the glaze — and a colour that shifts from pale at the rim to deep at the foot. A celadon that is uniformly one green, or that has a grey cast, was either fired without enough body reduction or applied too evenly.
Crazing in celadon is normal on porcelain and is not considered a defect in the tradition, but it does mean the surface is not suitable for food that will be left standing. On functional work, adjust the silica up by 2 percent to reduce the expansion mismatch.
Steps
- Weigh all seven materials and combine them dry, mixing the iron oxide last after breaking up any lumps.
- Add water and mix for eight minutes; celadon needs longer mixing than a low-fire glaze.
- Adjust to 1.50 specific gravity and sieve through 100 mesh.
- Pour the interior, drain, and let it dry until the surface is matte.
- Dip the exterior for three seconds to build 0.8 to 1.2 mm of glaze.
- Wipe the foot and load on a thin layer of alumina wax or a washed shelf.
- Fire in reduction: light from 900 to 1200 degrees, medium from 1200 to cone 10.
- Record damper position, air setting and flue flame at every 50 degrees during the firing.
- Cool slowly to 1000 degrees, then let the kiln cool naturally overnight.
Where it goes wrong
- Adding iron to deepen the colour. It goes olive; thickness is what deepens celadon.
- Starting reduction too late, after 1000 degrees. The ferrous conversion needs to start at 900.
- Applying at 0.4 mm. The result is a grey-white that is not celadon at all.
- Using a stoneware with 2 percent iron in the body. The body iron fights the glaze colour.
- Firing in oxidation through the end of the cycle, which turns the green yellow.
| Symptom | Cause |
|---|---|
| Celadon came out grey and opaque | heavy reduction throughout, or reduction continued past 1260 degrees. |
| Colour is yellow-green rather than blue-green | oxidation late in the firing, or too little calcium in the base. |
| Colour is pale and washed out | glaze applied too thin, under 0.5 mm. |
| Green with a dirty brown edge where the glaze thins | a high-iron stoneware body beneath a porcelain glaze. |
Recipe and schedule numbers here were recorded on the workshop’s own kiln. A different kiln, a different thermocouple position or a different clay batch will move the result, so treat every firing schedule as a starting point and keep your own log beside it.