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P380

Mid-temperature, smooth, medium plastic, vitreous, off-white burning, refined material, porcelainous stoneware for functional ware.

P380 is a classic white stoneware blend of ball clay, flint, feldspar and kaolin. It is similar to our cone 10 P580 (except it contains more feldspar and less clay and flint). It also has some added talc for extra maturity and some bentonite for added plasticity. P380 employs ball clay and kaolin (instead of straight kaolin) to give it extra plasticity, better drying and working properties at the expense of fired whiteness. This strategy produces a body easier to fit glazes to (because there is more room in the recipe for flint). Most people find that the tradeoff is well worth it, since bodies of this type are easier to form and dry and have greater strength in the dry state.

However, if you do not require the whiteness of P380 compared with our M340, we recommend you consider the latter. Although not nearly as white firing, it is even better from a working properties and drying point-of-view.

Process Properties

P380 is a smooth and slick and generates very little slip during throwing. It is a fine grained body that throws and dries quite well compared to all-kaolin porcelains. Its ball clay complement gives it a robust nature that makes it a good choice for machine forming and even hand building. P380 does not perform as well if it is too soft.

However, P380 is fine grained and thus it cannot be expected to dry and handle as well as a coarser stoneware. If you need to join sections, be sure to follow good practice (i.e. use low-water-content slip containing an aggregate like molochite, dry ware evenly, use pressure and lateral movement when joining, make ware with an even cross section). Keep the focus on evenness of drying rather than speed of drying.

Firing

P380 fires to a clean fully vitrified off-white dense product at cone 6. It maintains similar color through the cone 5-7 range. At cone 4 the color is whiter and much less stoney looking. Since the body usually reaches zero porosity at cone 6, it softens and is subject to warping and sagging during firing. You thus need to make sure your kiln shelves are flat and give attention to the cross section of your ware to make sure it has inherent strength to resist warping.

Since P380 is formulated to incorporate ball clays, it does not burn as white as our P300 or M370. If the color is white enough, then P380 is the body of choice. If you need a vitreous body that is whiter, use P300. If you need one that is whiter and vitrification is not as important, then M370 may be better.

Glazing

Since P380 fires to a clean homogeneous very light buff color, you will find that glazes and colors are quite bright on it compared to stoneware bodies. They may also exhibit slightly different surface characters because there are more fluxes in the vitreous body to interact with the glaze.

P380 is not guaranteed to fit the same as glazes and slips that you may have used on our other bodies. To prevent crazing and shivering, and assure that ware is strong, we recommend that you test the glaze fit using a boiling water:ice water stress-test. Also, note that this body can be significantly weakened if the glaze does not fit. If you need assistance to adjust the thermal expansion of your glazes to fit, please call Plainsman for information.

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: 4.5-5.5%
 Dry Strength: n/a
 Water Content: 20.0-21.0%
 Drying Factor: C120
 Dry Density: n/a

Sieve Analysis (Tyler mesh):

     +48: 0-0.1%
   48-65: 0.0-0.1
  65-100: 0.1-0.4
 100-150: 0.2-0.5
 150-200: 0.5-2.0
 200-325: 5.0-8.5

Fired Shrinkage:

 Cone 4: 6.0-7.0%
 Cone 5: 6.3-7.3
 Cone 6: 6.6-7.6
 Cone 7: 7.0-8.0

Fired Absorption:

 Cone 4: 2.0-3.0%
 Cone 5: 0.2-0.5
 Cone 6: 0.0-0.3
 Cone 7: 0.0

Chemical Analysis

 CaO       0.2
 K2O       3.6
 Li2O      0.7
 MgO       0.5
 Na2O      1.5
 TiO2      0.4
 Al2O3    17.7
 SiO2     71.0
 Fe2O3     0.4
 LOI       4.0%