Saint John's Clay
Local Stoneware Clay Processing
When Richard Bresnahan returned to Saint John's University in 1979 to establish the Saint John's Pottery, he began the work of searching for local clay suitable for high-temperature wood firings based upon what he had learned during his apprenticeship with the Nakazato family in Japan.
Asian cultures have a long and rich history working in clay. Japanese ceramic traditions varied widely from region to region - usually based on available clay. For example, feldspar-rich clay offers spotted and textured surfaces, while clay high in iron content produces ceramics rich with reddish brown tones when fired.
In central Minnesota, clay deposits were churned by generations of glaciers pushing down from northern Minnesota and southern Canada thousands of years ago, leaving irregular veins of clay and glacial till. Each clay deposit, with natural variations in mineral content, requires a series of trials to evaluate strengths and weaknesses.
For the seaching potter, another challenge may be finding a deposit large enough to provide a consistent material over many years. Through local contacts Bresnahan met Francis Schellinger, a woodworker and community leader, who led him to a large clay deposit that had been unearthed during road excavation.
Working with Saint John's University and Collegeville Township officials, the forty foot deep deposit was excavated and delivered to Saint John's for storage and use. While the excavation represents an expensive initial investment, a high quality material has been secured for more than ten generations into the future.
Saint John's Clay is a dark, grey-black material with a very fine particulate size. Gypsonite (or selanite) crystals grow naturally inside the clay. Two iron stone seams found within the clay deposit are ideal for ceramic painting designs. When mixed with 20% ball-milled silica sand, the clay body fires to stoneware temperatures in oxidation.