Cone 10R Grolleg porcelain vs American ball clay/kaolin porcelain

Wednesday 25th July 2012

Typical pottery porcelains are variations on the traditional triaxial body and commonly contain around 50% clay, either insight-live.com/material/925">kaolin, ball clay or a mixture. Since the clay fraction is normally the largest source of iron and titanium impurities, its purity has a major influence on fired whiteness—especially in reduction.

These mugs were fired in the same kiln load at cone 10R and have the same clear glaze, G1947U. The mug on the left is a Grolleg kaolin porcelain (50% Grolleg kaolin, 25% silica and 20% Mahavir feldspar, 5% bentonite). The one on the right is 15% M23 ball clay, 40% #6 Tile kaolin, 15% Nepheline, 25% silica, 3% bentonite. The grey is the cumulative effect of the impurities in these clays.

Grolleg is considerably more expensive, but this is one place where the extra purity is plainly visible. Want to push whiteness even further? Use an ultra-low-iron New Zealand kaolin and replace ordinary bentonite with Veegum or another clean-burning plasticizer.

Pages that reference this post in the Digitalfire Reference Library:

Grolleg Kaolin, Tile #6 Kaolin, Primary Clay, Porcelain

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