M370

Middle temperature, smooth, very plastic, white-firing, semi-vitreous, refined material body for functional stoneware. M370 is a response to customer requests for a more plastic white-firing material with adequate margin for overfiring and resistance to warping. Thus, unlike our porcelains such as P380 and P300, M370 is semi-vitreous (it is somewhat porous at cone 5-7). Also, it employs high quality ingredients and utilizes 5 clays and two feldspars to minimize effects if material changes. Compared to similar competitor bodies M370 is whiter. It is white enough that M370 powder is a good base for slips to be painted on the ware assuring the best drying and fired fit possible. M370 also has a very similar high temperature sister body named H570.

Process Properties

Since M370 is less vitreous it does not require as much feldspar. This enables us to maximize the clay content and create a body of greater plasticity. Since M370 is still a fine grained plastic body good drying practice is necessary. If you need to attach elements (i.e. handles) use slip with a low water content and apply as much pressure and latteral movement as possible during the joining process.

Firing

Cone 6

M370 is semi-vitreous at cone 6 (unlike P300 and P380 it does not reach zero absorption during typical electric firing to cone 6). M370 is quite white compared to vitreous porcelains where the color of even small amounts of iron is amplified by the more glassy nature. If overfired M370 will display less tendency to bloat, stick to shelves, and glue lids to lips of ware than would a vitreous stoneware or porcelain (unless it is overfired). However, M370 is vitreous compared to stoneware bodies.

There is an important caution with M370, it is quite high in free quartz. This is an asset to achieving glaze fit but also means that you cannot cool the kiln through quartz inversion temperatures (e.g. 1024F) too quickly during firing or dunting cracks will occur (especially large bowls and plates). If you glaze-fire a piece more than once you must also be careful during heatup through this temperature. Also, be aware that cooling your kiln too quickly through any stage may set up temperature gradients within pieces that will continue even if you attempt to slow-cool through inversion temperatures.

Glazing

Since M370 fires to such a white color, you will find that glazes and colors are quite bright on it compared to stoneware bodies.

Like any porcelain type body, M370 is more inclined to craze glazes than a our native stonewares. To prevent crazing and shivering, and assure that ware is strong, we recommend you test the glaze fit using a boiling water:ice water stress-test. This is especially important on this body because it has a slight porosity and can soak up some water if the glaze provides cracks (this will lead to moisture expansion and more crazing). If you need assistance to adjust your glazes, please contact us for assistance.

Glaze Recipes

You can develop a compatible glossy or matte base for this body from our suggested starting point base recipes available on our Internet web site at http://digitalfire.com/education/glaze/cone6.htm. Information is given on how to fit the glaze to your body and how to customize it it for colors, opacity, speck, variegation, etc. 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.

Physical Properties

 Drying Shrinkage: 5.5-6.5%
 Dry Strength: n/a
 Water Content:21.7-22.7 Drying Factor: C120
 LOI: 5.0-6.0%
 Dry Density: n/a

Sieve Analysis (Tyler mesh):

   48-65: 0.0-0.2%
  65-100: .01-0.3
 100-150: 0.1-0.4
 150-200: 1.0-4.0
 200-325: 8.0-11.0

Fired Shrinkage:

 Cone 4: 6.0-7.0%
 Cone 5: 6.5-7.5
 Cone 6: 6.5-7.5
 Cone 7: 7.0-8.0

Fired Absorption:

 Cone 4: 3.0-4.0%
 Cone 5: 1.7-2.7
 Cone 6: 1.0-1.7
 Cone 7: 0.5-1.5

Chemical Analysis

 CaO       0.2
 K2O       1.2
 KNaO      0.1
 MgO       0.4
 Na2O      2.3
 TiO2      0.6
 Al2O3    25.3
 P2O5      0.0
 SiO2     61.8
 Fe2O3     0.5
 FeO       0.0
 MnO       0.0
 LOI       7.5%

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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