The geo-chemistry behind Rookwood pottery

When most of us gaze upon an eight-place setting of fine porcelain china or a curvaceous ceramic vase, we see exactly that, but when Jim Robinson of Rookwood Pottery looks at such objects, he sees rocks, as I learned recently when I interviewed Robinson about his role as the venerable art pottery firm's glaze chemist.

His interest in rocks and geology came early. “When I was in high school in 1967,” he says, “I had a great professor, Richard Tremblay, who got into plate tectonics just as it was emerging. He explained to us how the surface of the planet was skidding around, powered by these upwellings of magma, and how when two plates encountered each other, one went down into the subduction zone and the other sprouted mountains. Well, I came seriously unglued when I heard that, and I’ve been reading about rocks and geology ever since.”

To put it mildly, this love of rocks and minerals has completely colored Robinson’s world. “I’m looking out a window now at a brick building,” he tells me as we are chatting over the phone. “Every brick building is made out of different clays. Some are kind of taupe gray. Some are really deep rust. Every brick is different because each comes out of a different hole in the ground. That just blows my mind.” More particularly, Robinson’s romance with stone has had a profound impact on his work as a ceramist. “Once you get an image in your mind of the earth and how active it is,” he says, “you start to put two and two together. You think, ‘That’s where the minerals are.’”

One mineral Robinson knows well is feldspar, two of whose alkalis, potash and soda, are common ingredients in clay. Potash and soda are easy to find, their ubiquity nothing more—or less—than the product of deep time. “The reason why a clay industry developed here in the Midwest is in large part because of the Appalachian Mountains,” Robinson begins. “When feldspar weathers, it turns into kaolin, the stuff porcelain is made of. The potash, soda, and calcium that’s locked up in the feldspar erodes out, running all the way to the sea—that’s why the sea is salty. However, the clay ingredients—minerals like pyrophyllite and silica—settle in places like Georgia and Kentucky, Tennessee and Ohio. It’s the coolest damn thing.”