Paper No. 56-18
Presentation Time: 8:00 AM-12:00 PM
THE ART AND SCIENCE OF THE GLACIAL LAKE CLAYS OF THE SUGAR CREEK VALLEY, BRADFORD COUNTY, PENNSYLVANIA
During the retreat of the Wisconsinan glaciation, the mouth of Sugar Creek in Bradford County, Pennsylvania was dammed by the receding ice sheet; thus flooding Sugar Creek and its tributaries, and creating a glacial lake. Glacial flour settled to the lake bottom and accumulated varved clay deposits locally exceeding 70 feet thick. Six samples of clay were taken from the upper reaches of the Sugar Creek lake deposit within the East Troy 7.5-minute quadrangle and were characterized for its potential as a ceramic art medium. X-ray diffraction of the clay shows an average mineral composition of 49% mica, 29%, quartz, 14% chlorite, 6% plagioclase, 1.5% dolomite, and 0.5% calcite. Firing test shows a limited range from bisque to maturity of 1900° F to 2100° F. Vitrification occurs at ~2100° F. The clay has a moderate to high plasticity, a water of plasticity of 21.96% to 25.25%, linear dry shrinkage of 6% to 8.5%, moderate to high green strength, and moderate to poor bonding strength. All samples classify as clay to silty clay on the USDA textural triangle. Test samples prove the clay can be used for small pots, terra cotta sculptures, and ornamental tiles. Glazing requires a low-fired ceramic glaze, such as used in slip casting, due to the clays tendency to bloat or melt at ~2200° F. Because the glacial lake clay will slump when undercut, as well as cause significant alterations to the local hydrogeology, this clay is not a commercially viable resource with exception to the casual hobbyist and the low-volume producing potter.