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P300 is a mix of plastic Georgia kaolin, nepheline syenite, 25% silica, raw bentonite (to augment plasicity) and a small amount of talc (for fired maturity control). P300 is not translucent at cone 6. It is the whitest body we can make without using expensive white plasticizers or overseas kaolins.
We have increased the silica from 17% to 25%. This makes it much easier to fit glazes (crazing was an issue in the past). Plasticity and workability have been improved by a shift to a more plastic kaolin and a bentonite addition (drying performance is still excellent). If you use M370 we recommend you try this body, it feels alot different that M370. You may be pleasantly surprised!
P300 is a smooth and slick fine grained body. Since it relies almost entirely on plastic kaolin for workability the pugged material has a unique distinct feel that many prefer to high ball clay porcelains. Because of the added bentonite, plasticity is excellent (as good or better than M370).
P300 is a porcelain, so it does not dry as as well stoneware. But the drying is still very good. Most people will have no trouble drying typical ware. Of course, large flat plates and tiles will require extra care. The key to success is to prevent gradients in water content across the ware during all stages of drying (at no time should one part of a piece by significantly drier than another).
P300 is intended to vitrify around cone 7 and have just a little porosity at cone 6 (thus it resists warping and crazing while still being very strong). It has a fairly high fired shrinkage so ware must be able to slide against the shelf to prevent warp and sticking (of course it is wise to kiln wash the shelves also). Endeavor to make ware of even cross section, this will produce inherent structural strength to resist warping.
P300 fires a little whiter than M370, significantly whiter than our P380 but nearly nearly as white as Polar Ice.
In the past P300 was difficult to fit glazes to (because of its low (17%) silica content). Starting in Fall 2015, we have raised that to 25%, this will mean that most glazes will fit. We suggest starting with our Whiteware M370 transparent recipe G2926B (available on our Liner and Base Glazes page). We manufacture these but also provide the recipes if you want to mix your own (there are links to the recipes). The G2934matte base recipe on that page also works well on P300. If you still have crazing issues, then try the lower expansion version (numbered G2926J), there is a link to it on the G2926B recipe page (or just google "G2926J recipe").
For slip decoration, be careful to match drying and fired shrinkage and thermal expansion of the slip with the body.
Drying Shrinkage: 5.0-6.0% Dry Strength: n/a Water Content: 21.5-22.5% Drying Factor: c110 Dry Density: n/a
48-65: 0.0-0.1% 65-100: 0.0-.1 100-150: 0.0-0.1 150-200: 0.3-0.8
Cone 5: 6.5-7.5% Cone 6: 7.0-8.0 Cone 7: 7.5-8.5
Cone 5: 2.0-3.0% Cone 6: 0.25-0.75 Cone 7: 0.0-0.25
CaO 0.3 K2O 2.1 KNaO 0.1 MgO 0.1 Na2O 0.6 TiO2 0.8 Al2O3 25.1 SiO2 63.1 Fe2O3 0.3 FeO 0.0 LOI 6.6%