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

M350 is the material of choice if you need to make functional ware from a brown burning body. It is processed to 100 mesh particle size and is intended to produce ware with a clean, unblemished glaze surface.

M350 is very similar in composition to M390 and shares the very fine and smooth natural character and plasticity. Its lighter color will be suitable for all but very specialized glaze effects requiring a dark burning body. M350 contains 5 different clays each of which is quite balanced on its own and it is a body over which we have a lot of consistency control.

Process Properties

M350 has medium plasticity and feels slick on the wheel and generates significant slip during throwing. While you will find it dries well for smaller items, as with any other fine-grained material, care and attention in drying are necessary in making larger pieces, especially 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 elements (i.e. handles) use slip with a low water content and apply as much pressure and lateral movement as possible during the joining process.

If you need an all-around coarser material, M375 is another possibility, however it can produce pinholing in some glazes and will tend to produce rough glaze surfaces where grog exposes through thinly glazed sections (i.e. mug lips).


These M350 fired bars show the progression of color from cone 4 (bottom) to cone 8.

M350 fires to a leather brown color at cone 6. In the cone 4-5 range there are pinkish and more variegated tones in the brown color. At cone 7 the body burns to a dense grey brown. If this M350 is fired beyond cone 7 it will begin to bloat, thus we recommend cone 5 for the warmest color possible, and cone 6 for better hardness and functional strength. We try to maintain this body at about 1.0-1.5% porosity at cone 6, thus is it more vitreous than M390. M350 does work in reduction at cone 4-6 whereas M390 is too vitreous because of its high iron and M340 because of its talc complement.

M350 is fine-ground and thus fires to a homogeneous color compared to M332, which burns to a darker more earthy variegated surface. M390 has a similar character but fires to much darker shades.


M350 is quite fine and fires to 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 mute them to some extent so that glazes will not be as vivid as they would be if used on porcelain.

M350 is high in silica and will accept most typical cone 6 glazes without producing crazing. However, crazing is possible on M350 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.

Although M350 fires to a reddish tone at cone 4-5, keep in mind that the color will darken considerably under a transparent glaze because the glaze fluxes the surface of the clay advancing its color to that of a hotter firing.

Glaze Recipes

Please check the M390 data sheet for recommendations for glazes. We specifically recommend the base Alberta Slip GA6-A as a liner glaze. 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 M350, 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.

Thermal Expansion

We do not supply a thermal expansion value. The reason is that such numbers often mislead users. First, a body has different thermal expansion characteristics when fired at different temperatures, schedules and atmospheres. Dilatometers are only useful when manufacturers can measure bodies and glazes over time and in the same firing conditions. If a chart is supplied here, please view only as a way to compare one body with another.

Another significant issue is that many customers compare measured thermal expansion numbers with calculated values of glazes in efforts to fits those glazes to a body. This does not work. Calculated values are relative only and have limitations that must be understood. The best way to fit glazes to your clay bodies is by testing, evaluation, adjustment and retesting. For example, if a glaze crazes, adjust its recipe to bring the expansion down (using your account at insight-live), fire a glazed piece and thermal stress it (300F into ice-water). If it still crazes, repeat the process.

If we recommend a base clear or glossy glaze, try calculating the expansion of that as a rough guide to know whether your glazes will fit.

Physical Properties

 Drying Shrinkage: 6.0-7.0%
 Dry Strength: n/a
 Water Content: 20.5-21.5%
 Drying Factor: c120
 Dry Density: n/a

Sieve Analysis (Tyler mesh):

   48-65: 0.0-0.1%
  65-100: 0.1-0.5
 100-150: 2.5-3.5
 150-200: 4.5-6.5
 200-325: 7.0-10.0

Fired Shrinkage:

 Cone 4: 4.0-5.0
 Cone 5: 4.5-5.5
 Cone 6: 5.0-6.0
 Cone 7: 5.5-6.5

Fired Absorption:

 Cone 4: 4.0-6.5
 Cone 5: 3.5-5.0
 Cone 6: 1.5-2.5
 Cone 7: 1.0-2.0

Chemical Analysis

 BaO       0.3
 CaO       0.2
 K2O       2.2
 MgO       0.7
 Na2O      0.1
 TiO2      0.7
 Al2O3    17.2
 P2O5      0.1
 SiO2     68.5
 Fe2O3     2.6
 MnO       0.0
 LOI       7.5%


M350 vs M390 at cone 6. Inside glaze is Alberta Slip GA6-A base, outside is Alberta Slip rutile blue. By Tony Hansen.

M350 cylinder with Alberta Slip rutile blue glaze fired to cone 6.

Safety Data Sheet

Click here for web view.

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