M390

M390 is a smooth, very plastic red stoneware for functional ware at mid range. It carries more native Redstone than any of our other bodies, which is where the depth of colour comes from, and it is a joy to work with on the wheel.

M390 is a finely ground, very plastic, semi-vitreous stoneware that fires dark red-brown. It carries more native Redstone than our other bodies and is processed to 60 mesh, which is why the fired surface comes out smooth.

The clay comes from quarries near the plant. It has not travelled a long distance, or come in from overseas, so its environmental footprint is smaller than that of clays that must travel to get here.

Colour builds with temperature — a warm, toasty red at the low end of the range, deepest at cone 6. It is a traditional, earthy red, the colour of old clay cookware.

The iron works in your favour under reactive and rutile glazes, which come up richer than they do on a white clay. It has practical consequences too: unglazed surfaces will seep slowly over time, and pieces heat up in a microwave.

Working properties

High plasticity with a smooth feel. If the clay is too soft it throws a lot of slip, so keep it on the firm side and go easy on the water.

Drying evenly matters more than drying quickly. Take extra care with larger pieces.

Fired colour & cone behaviour

A warm, toasty red at the low end of the range. Cone 6 is where the red is deepest and where we recommend firing it.

By cone 7 the colour shifts toward brown, and the body may warp — it will not bloat, but the movement is worth knowing about on flatware and wide forms.

Glazes & glaze fit

There is enough silica in the body that M390 takes most typical cone 6 glazes without crazing, though a glaze high in sodium can still craze.

Clear glazes are the exception. On a body this dark they tend to come up cloudy and muted, so test before you count on one. Reactive and rutile glazes are where M390 is at its best.

Fire a test tile before you commit a kiln load, so you know the glaze fits.

Specifications

Type: Mid-fire red stoneware · semi-vitreous · functional ware

Texture: Finely ground and smooth, processed to 60 mesh · exceptional plasticity

Usage: Throwing · functional ware · reactive and rutile glazes. Not suitable for slip casting — soluble salts in the clay prevent it deflocculating.

Temperature: Cone 5 · 6 · 7 (cone 6 = 1222 °C / 2232 °F)

Colour: Deep, warm red — a traditional, earthy look

Shrinkage: Dry 6.4–7.5% · fired 4.4–5.5% at cone 5, 4.8–5.1% at cone 6, 5.1–5.3% at cone 7

Absorption: Cone 5 2.8–3.0% · cone 6 1.7–2.0% · cone 7 1.0–1.3%

Chemical analysis: SiO₂ 65.6 · Al₂O₃ 22.4 · Na₂O 2.6 · K₂O 1.2 · TiO₂ 0.7 · Fe₂O₃ 0.5 · CaO 0.2 · MgO 0.2 · MnO 0.0 · LOI 6.4%

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.