M340

M340 is one of our most popular general-purpose clay bodies — plastic, medium-fired and buff burning, and it throws and hand-builds equally well. Best fired to cone 6.

M340 is mined locally, using various stoneware clays. It is one of our most popular general-purpose bodies and handles most of what a mid-range studio makes — thrown work, hand-built work, and everything in between.

The particle size distribution is what makes it behave the way it does. The range of sizes gives the clay its dry strength; the coarser size allows water to escape out of the wall structure, so work dries more readily than a dense uniform fine particle body.

Fired, colour ranges from a straw at cone 4 to a warm buff-grey at cone 6 and 7.

Working properties

A good clay to both throw and hand-build with. It has a plastic, smooth and subtle grained texture to it, and excellent dry strength that comes from the diverse particle size distribution.

The clay body is fine enough that 95% of a raw sample washes through a 200-mesh sieve without any grinding.

Take care with larger pieces — flat plates, shallow bowls and sculptural work. Evenness of drying matters more than speed.

Fired colour & cone behaviour

Colour ranges from a straw at cone 4 to a warm buff-grey at cone 6 and 7.

Cone 5, 6 and 7 are all within range, and it is recommended to fire to cone 6. Witness cones are encouraged to verify the firing temperature.

Glazes & glaze fit

M340 is high in silica and will craze fewer glazes than our porcelain bodies. Crazing is still possible with a glaze high in sodium, or one short on silica or alumina — an unbalanced glaze carrying a lot of feldspar and little kaolin or flint is the usual culprit.

The iron in the body mutes bright glaze colours compared with the same glaze on porcelain. Applying an engobe can help with colour development.

If you are making functional ware, a boiling water to ice water immersion test will tell you whether the glaze really fits.

Specifications

Type: Medium-fired buff burning stoneware · general purpose · vitreous

Texture: Plastic, smooth, with a subtle fine-grained texture

Usage: Throwing and hand-building · general purpose stoneware

Temperature: Cone 5 · 6 · 7 — it is recommended to fire to cone 6 (1222 °C / 2232 °F). Witness cones are encouraged to verify the firing temperature.

Colour: Colour ranges from a straw at cone 4 to a warm buff-grey at cone 6 and 7

Shrinkage: Dry 6.0–7.0% · fired 5.0–5.5% at cone 5, 5.5–6.5% at cone 6, 5.8–6.8% at cone 7

Absorption: Cone 5 1.3–1.8% · cone 6 0.7–1.0% · cone 7 0.3–0.5%

Chemical analysis: SiO₂ 69.2 · Al₂O₃ 17.7 · Fe₂O₃ 1.4 · K₂O 2.1 · MgO 1.2 · TiO₂ 0.6 · CaO 0.2 · Na₂O 0.1 · MnO 0.0 · LOI 7.5%

Every figure is a measured range from the Plainsman lab, not a single nominal number. Cone equivalents are Orton self-supporting cones at 108 °F/hr.