THE GEOLOGY OF ART: PRELIMINARY RESULTS FROM A MINERALOGICAL STUDY OF COLORANTS IN CERAMIC GLAZES

Glazes have been applied to pottery for both mechanical and decorative purposes for thousands of years. Early cultures learned that glaze color was largely controlled by combinations of mineral additives such as hematite (Fe^2/3+), chromite (Cr³⁺), or malachite (Cu²⁺), and they devised many successful recipes that are still popular today. Hundreds of new minerals have been found since these glazes were first introduced and many, probably most, have yet to be evaluated as colorants in ceramic glazes. In the summer of 2012, a team of three geologists (including two undergraduate students), and a ceramic artist, began experimenting with approximately 100 different minerals as coloring agents in a leach clear glaze. We did not follow strict ceramics procedures in determining the correct proportions of key glaze ingredients (e.g., silica and alumina). Instead, we determined the weight percent of each targeted cation and produced sample glazes containing 1%, 2%, 5%, 10% and 15% of that cation for each mineral that was selected. Each glaze combination was applied to bisque-fired test plates and fired under reducing conditions in a gas kiln. Duplicate test plates were fired in lower temperatures in an oxidizing electric kiln. Test plates were later used to produce art piece mosaics illustrating three important concepts in science; gradualism, punctuated equilibrium and the periodic table of the elements. Our results were mixed. Some mineral colorants behaved as expected (e.g., Cu), but most imposed inconsistent colors under oxidizing or reducing conditions, or both. Low mineral concentrations (<5%) generally did not color the glaze and high concentrations (15%, occasionally 10%) commonly made glazes dark and opaque. These preliminary data will be used to refine and develop a more comprehensive study for the summer of 2013. We will use minerals that showed promising results in leach clear glaze and add them to other glaze combinations.