GRKA
A kaolin remarkably low in titania · Where a thin porcelain wall needs to fire translucent · Residual mica brings potassium, so it contributes a little flux · Moderate plasticity, so a body built on it usually takes a plasticiser
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Grolleg is a kaolin remarkably low in titania, which is the impurity that most gets in the way of a thin porcelain wall firing translucent. It also carries residual mica, which brings a little potassium with it.
Grolleg is a kaolin chosen for what it does not contain. Titania scatters and absorbs light, and it takes very little of it in a body to dull a thin porcelain wall; Grolleg runs remarkably low in titania. Its iron is ordinary for a kaolin, and iron is not what decides translucency. It also carries residual mica, which brings potassium with it, so the clay contributes a little flux of its own. Its plasticity is moderate, enough that a body built on it usually takes a plasticiser as well. Translucency is still a property of the fired body rather than of the clay — wall thickness, flux level and firing all decide it.
