Our most popular mid-temperature, smooth, plastic, semi-vitreous, buff burning, native functional stoneware.
Three porcelains and a buff stoneware with transparent base glaze at cone 6.The M340 is made from a combination of our A3 and B stoneware materials (as are H550, Buffstone, L212). It is our most popular body (widely used in schools, by hobbyists, and professional potters. Compared to bodies made from refined industrial minerals, M340's diversity of ultimate particle sizes produces a body of much higher dry strength. Its parent materials are also highly consistent, pure, and free of foreign particles. In fact, even without grinding, 95% of a raw sample of M340 will wash through a 200 mesh sieve.
M340 has medium to high plasticity and feels smooth (having a slight texture). There is some distribution of particle sizes in the plus 200 mesh range, these provide channels for faster drying than other bodies you may have used. You should have few problems drying smaller pieces, but care and attention are necessary when 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 drying of the entire piece to effect a more even process.
Fired test bars of M340 (left) and M325. Fired at cone 8, 7, 6, 5 and 4 (top to bottom).
M340 fires from a straw color at cone 4 to patchy stone-grey-buff at cone 6 to grey by cone 8 (the greying begins by cone 7). M340 is best used at cone 6. This temperature is a functional compromise between the maximum vitrification of cone 8 (where it will also tend to warp or bloat) and the higher porosities in the cone 4-5 range. We typically add 2-3% talc flux to maintain fine control over the body's fired maturity at cone 6 (and reduce the incidence of quartz inversion cracking problems).
Fired test bars of M340GS from cone 8 (top) to cone 4.
M340 Speck: This has 0.2% manganese granular added. IOt produces a fine black fired speck that will bleed up through glazes producing a pleasing visual character for some applications. However this body must not be fired higher than cone 6 or it will blister. Since slight overfiring is unavoidable in typical hobby kilns it is better to fire lower (i.e. cone 5) to avoid loss of ware.
M340 is quite fine particled in its natural state and takes glazes very well, producing fine homogeneous surfaces. It is high in silica and will craze fewer glazes porcelains. However crazing is possible 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 silica). As a general rule, unbalanced glazes containing high feldspar and little kaolin or silica are usually a problem. For functional ware check glaze fit using a boiling water:ice water immersion test.
Since M340 does contain some iron oxide, brightly colored glazes will tend be muted compared to porcelain. This can be handled by using a well fitted slip between body and glaze or opacifying the glaze more.
We specifically recommend liner and base glazes at our Liner and Base Glazes page. (e.g. M340 Transparent, Matte Base). We manufacture these but also provide the recipes if you want to mix your own.
For slip decoration, be careful to match drying and fired shrinkage of the slip with the body since low temperatures generate little glass to adhere the slip.
The chart shown was produced from a specimen fired once to cone 6 in the Plainsman lab and tested in an Orton dilatometer. If you fire to a different temperature, employ different heatup or cooldown rates, or glaze-fire more than once the thermal expansion in your ware may be different than this chart indicates.
Thermal Expansion Chart. Average: 5.5.
Drying Shrinkage: 6.0-7.0% Dry Strength: 800 psi Water Content: 20.0-21.5% Drying Factor: C120 Dry Density: 2.0
Sieve Analysis (Tyler mesh):
+48: 0.0-0.2% 48-65: 0.2-0.6 65-100: 0.5-2.0 100-150: 1.0-2.0 150-200: 1.5-4.0 200-325: 7.0-10.0
Cone 4: 4.0-5.0% Cone 5: 4.5-5.5 Cone 6: 5.0-6.0 Cone 7: 5.5-6.5
Cone 4: 4.0-5.5% Cone 5: 2.5-4.0 Cone 6: 1.5-2.5 Cone 7: 1.0-2.0
CaO 0.2 K2O 2.1 MgO 1.2 Na2O 0.1 TiO2 0.6 Al2O3 17.7 P2O5 0.0 SiO2 69.2 Fe2O3 1.4 MnO 0.0 LOI 7.5%
M340 at cone 6. Kathy Ransom.
Safety Data SheetClick here for web view (format adheres to Globally Harmonized System of Classification and Labelling of Chemicals - GHS)
|Plainsman Clays Ltd.|
702 Wood Street, Medicine Hat, Alberta T1A 1E9
Phone: 403-527-8535 FAX:403-527-7508