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M390

Mid-temperature, finely ground and smooth, very plastic, semi-vitreous, dark red brown burning native body for functional ware.

These fired bars show the progression of color from cone 4 (bottom) to cone 8 (porosity and fired shrinage are also indicated).

M390 fires very dark and is the material of choice for dark burning functional ware. It contains more of our native Redstone material than any other body. It is one of several bodies that we process to 100 mesh particle size and is intended to produce ware with a clean, unblemished glaze surface.

M390 is very similar in composition to M350 and shares the very fine natural smooth character. It is however more plastic. Its darker color tends to limit it to specialized glaze effects. M390 contains 5 different clays, each of which is quite balanced on its own.

Process Properties

M390 has high plasticity and feels slick. It generates significant slip during throwing. Care and attention during drying are a must, especially with larger pieces, flat plates, shallow bowls, and sculptural ware. Make sure that the focus is on evenness of drying rather than speed; if sections of a piece dry faster, then either slow these sections down or slow down the entire piece. If you need to attach pieces (i.e. handles) use slip with a low water content and apply as much pressure and lateral movement as possible during the joining process.

Firing

M390 is a fairly high iron body and thus burns red to brown as it matures. At cone 3-4 it is a very warm toasty red. The red intensifies to cone 6 and turns brown by cone 7. We maintain the porosity at about 1.75-2.0% at cone 6 to hold onto the red color.

Transparent glazes will darken the color of the underlying body. If you fire to cone 7 keep in mind that accidental over firing could take it into the warping or bloating territory of cone 8. If you fire to cone 4, be aware that porosity is too high (and strength likely too low) for practical functional ware. Cone 6 is the best compromise of color, stability and strength.

Glazing

This mug is made from M390 and glazed with Alberta Slip rutile (outside) and GA6-A Alberta Slip base (inside).

M390 is quite fine and produces a homogeneous fired surface for most glazes. Since it is a dark stoneware, the iron in the clay will bleed into glazes and colors and significantly stain or mute them (compared to porcelain). On the other hand, this effect will enhance the appearance of earthtone and variegated glazes.

M390 is high in silica and will accept most typical cone 6 glazes without producing crazing. However, crazing is possible on M390 if a glaze is high in sodium (i.e. from soda feldspar or nepheline syenite) or is very low in silica or alumina (little clay or flint). As a general rule, unbalanced glazes containing high feldspar and little kaolin or flint are usually a problem. For functional ware we recommend you check glaze fit using a boiling water:ice water immersion test. Please contact Plainsman if you need help to adjust your glaze.

Transparent glazes: Although M390 fires to red at cone 4-5, keep in mind that the color will darken considerably under a transparent glaze because the latter fluxes the surface of the clay. Worse yet, red clays like this are ugly under transparent glazes. But they are stunning under an amber transparent like GA6-A Alberta Slip base. Click the photo of the mug here to see it on the inside.

Glaze Recipes

The liner and base glazes at our Liner and Base Glazes page are also useful (any glaze that works on M340 will likely work on M390, although somewhat muted by the iron in the clay). We manufacture these base glazes but also provide the recipes if you want to mix your own.

Physical Properties

 Drying Shrinkage: 6.0-7.0%
 Dry Strength: n/a
 Water Content: 19.5-20.5%
 Drying Factor: c130
 Dry Density: n/a

Sieve Analysis (Tyler mesh):

     +65: 0.0-0.2%
  65-100: 0.5-1.5
 100-150: 4.5-7.5
 150-200: 7.0-10.0
 200-325: 10.0-15.0

Fired Shrinkage:

 Cone 4: 4.5-5.5%
 Cone 5: 5.0-6.0
 Cone 6: 5.5-6.5
 Cone 7: 5.5-6.5

Fired Absorption:

 Cone 4: 4.0-5.5%
 Cone 5: 2.5-3.5
 Cone 6: 1.5-2.5
 Cone 7: 0.5-1.5

Chemical Analysis

 BaO       0.3
 CaO       0.3
 K2O       2.3
 MgO       0.7
 Na2O      0.1
 TiO2      0.7
 Al2O3    16.3
 P2O5      0.2
 SiO2     68.3
 Fe2O3     3.6
 MnO       0.0
 LOI       7.2%


Logo Plainsman Clays Ltd.
702 Wood Street, Medicine Hat, Alberta T1A 1E9
Phone: 403-527-8535 FAX: 403-527-7508
Email: plainsman@telus.net
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