M332

Description

Mid-temperature, sandy, plastic, semi-vitreous, warm medium brown, native throwing body. M332 is made from seven different native clay materials and it is generally used for two reasons: its appealing warm red fired color at cone 5-6 and its combination of a sandy texture and high plasticity. M332 is attractive when used with glazes that absorb and highlight body iron and with ware that leaves some bare patches of clay showing. M332 has exceptionally high dry strength.

Process Properties

M332 has a highly plastic base with a sand complement to add texture. While it throws very well and generates sufficient slip, it can be 'grabby' during throwing with care to make sure pressure surfaces are not well lubricated. Once you learn how to throw it you will be amazed at what it can do.

Cautions: Because of the sand content it can develop splits during construction or throwing if water is allowed to sit on the surface at stress points (i.e. the outer belly of a thrown vase). In addition, when pulling handles, you must develop techniques to minimize splitting. It is best to keep sponging of leather hard or dry ware to a minimum as this tends to remove fine particles at the surface and expose the coarser ones (a problem on the lips of functional ware. M332 needs to be dried with care to avoid cracking. Turn open shapes over as soon as they will support themselves and cover ware with cloth and plastic (not just plastic) to even out any gradients in water content.

Firing


M332 fired bars from cone 4 to 8 oxidation (bottom to top).

M332 burns to a warm brick-red at cone 3-5, shifting to a medium variegated red brown at cone 6, and finally to a grey brown by cone 8. If you want the attractive red color remember that M332 undergoes a sudden color shift from red to brown between cone 6 and 7. Fire carefully to avoid overshooting the target temperature and losing the red. The redish color depends on the body firing to 4-5% porosity.

To get the best defect-free surface please consider using a drop-and-hold firing schedule, for example the PLC6DS schedule. If crystallization during cooling is not an issue, glazes will give optimum results if slow-cooled also (e.g. the C6DHSC schedule).

Glazing


Since we add materials with coarser particles and impurities to give the surface a more earthy appearance you can expect that the body will not provide perfectly clean glazed surfaces for functional ware. Glaze disruptions such as small pinholes and specks will be common. You can often solve this by using a drop-and-soak firing schedule. In other cases it may be necessary to fire the bisque a little higher to expel more gases of decomposition.

Although M332 burns a warm red color at cone 5, if you apply a transparent glaze it will flux the surface and the color will likely darken and turn dark brown brown. Thus, if you need to achieve red glazed colors it may be necessary to fire at cone 3-4. Also, because this is an iron-brown burning body it will impose some of its color on all glazes, darkening them and muddying colors.

Caution About Clear Glazes


Clear glazes often do not work on dark bodies. The center mug is clear-glazed with G2926B (and is full of bubble clouds). This dark body (M390) is exposed inside and out (the other two mugs have the L3954B white engobe inside and midway down the outside). G2926B is an early-melter (starting around cone 02) so it is susceptible to dark-burning bodies that generate more gases of decomposition.

Left mug: The outside glaze adds 4% iron to G2926B (the glaze was not screened, so iron particles are agglomerated and acting as a fining agent, removing the bubbles). Right mug: The whole thing is glazed with GA6-B Alberta Slip base glaze. These amber glazes have an added benefit: The color darkens over dark burning bodies (to almost black).

Glaze Recipes

Commercial brush-on glazes offer many colors and surfaces. For functional ware check for glaze fit (vital for quality functional ware). Do not assume food safety of brightly colored glazes in your kiln and with layering without a leach test (e.g. GLLE test). Consider using a transparent or white liner glaze for food surfaces.

Mixing your own glazes is practical (with our guidelines even beginners can make dipping glazes that go on silky smooth and evenly and dry in seconds). Be careful using recipes from the web. High-feldspar glazes (having more than about 35%) most often craze. Ones that rely on high melt fluidity to encourage crystallization and variegation (often because of excessive Gerstley Borate, lithium carbonate, zinc or Frit), view these with suspicion for leaching and cutlery marking; test them well (also test the additionless versions).

The best approach is to begin with good transparent bases you understand, do not craze, cutlery mark or leach. Our G2926B glossy and G2934 matte are frit-fluxed bases with documentation on use and adding stain, color and variegator additions. G2934 has significantly lower thermal expansion. The two can be mixed to fine-tune matteness and thermal expansion. For example, a 20:80 matte:gloss mix gives a silky matte for us. The gloss is dominant so a 50:50 mix is glossy, but with lower thermal expansion.

Consider also making glazes based on Alberta Slip (especially the GA6-B amber base) and Ravenscrag Slip. These materials have their own websites with lots of helpful information.

Crazing: Functional ware must remain craze-free (crazing is unsanitary and drastically reduces ware strength). Even though ware may not be crazed out-of-the kiln it may do so with time. Do cycles of a boiling water:ice water immersions (BWIW test) on a piece to test glaze fit (by stressing it to bring out any crazing or shivering tendencies).

Thixotropy: Many people mix their glazes the traditional way, just adding water until the slurry appears to be the right viscosity for dipping. However, if you want better application properties for one-coat dipping, consider creating a thixotropic slurry. Thixotropic glazes are creamy because they have been thinned and then gelled by the addition of a flocculant. They go on evenly, hang on without dripping and dry quickly. Achieving (and maintaining) this state involves targeting a specific gravity (usually around 1.43) and adding epsom salts (1-2g/1000g of powdered glaze).

This body is a great candidate for the engobe process, we recommend the L3954B recipe. It can be colored with stains or whitened with zircopax. It can be applied thickly as an engobe or thinly as a slip.

If you want to develop and mix your own glazes and engobes consider getting an account at insight-live.com. You can organize a methodical development program and adopt better methods of testing (e.g. melt fluidity, thermal stress, slip-fit tests).

Thermal Expansion

We do not supply thermal expansion values. If a chart is supplied here, please view it only as a way to compare one body with another. Please note that, although you may calculate the thermal expansion of a glaze, this cannot be done for clay bodies since they do not melt. The best way to fit glazes to clay bodies is by testing, evaluation, adjustment and retesting. For example, if a glaze crazes, adjust its recipe to bring the expansion down, fire a glazed piece and thermal stress it (using an IWCT test, 300F into ice-water). If it still crazes, repeat the process.

Physical Properties

 Drying Shrinkage: 6.0-7.0%
 Dry Strength: n/a
 Water Content: 19.5-20.5%
 Drying Factor: c332
 Dry Density: n/a

Sieve Analysis (Tyler mesh):

     +48: 0.1-0.5%
   48-65: 2.0-4.0
  65-100: 6.5-9.5
 100-150: 6.0-8.0
 150-200: 8.0-11.0
 200-325: 8.0-12.0

Fired Shrinkage:

 Cone 4: 3.0-4.0%
 Cone 5: 3.5-4.5
 Cone 6: 4.0-5.0
 Cone 7: 4.5-5.5
 Cone 8: 5.0-6.0

Fired Absorption:

 Cone 4: 5.5-7.5%
 Cone 5: 4.5-6.0
 Cone 6: 3.5-4.5
 Cone 7: 2.5-3.5
 Cone 8: 1.5-2.5

Gallery


M332 bowl by Louise Bouchard.


M332 with Ravenscrag and Alberta Slip floating blue glazes. Fired to cone 6 oxidation using the C6DHSC schedule.

Logo Plainsman Clays Ltd.
702 Wood Street, Medicine Hat, Alberta T1A 1E9
Phone: 403-527-8535 FAX:403-527-7508
Email: tim.lerner@plainsmanclays.com