25 Porcelain refers to a recipe of about 25% each of ball clay, kaolin, feldspar and silica. In this case the 25-porcelain employs Tile #6 kaolin and a Kentucky ball clay. Both of them contain raw bentonite to augment the plasticity and both have about 50% clay in the recipe. The Grolleg body requires more bentonite to achieve the same plasticity. In spite of the fact that the raw bentonite has a high iron content and it darkens the color, the Grolleg porcelain is still much whiter firing.
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