Investigation of Calcium Oxide (CaO) Effects in Crackle Stoneware Glazes

Crackle glazes for use on ceramic bodies are well-known in the ceramic art and may be defined as glazes whose tendency to craze is used for decorative effect. One of the important steps to understanding glazes and glazing is to have a good grasp of the properties the materials you are using and how they affect the glaze properties. The final properties of the glaze can be managed and evaluated by focusing on the oxide effects of the fired glaze. Calcium Oxide (CaO) is the principle flux in medium and high temperature glazes, beginning its action (within the glaze) around 1100 ？C. In this work the effect of CaO on the properties of crackle glazes was investigated. 5 different crackle glaze recipes containing different amounts of calcium oxide were prepared and fired at 1160 ？C degrees. Manganese (II) oxide (MnO) and Iron Oxide (Fe2O3) were used as coloring oxide. All the samples were characterized by X-ray fluorescence (XRF), X-ray diffraction (XRD), scanning electron microscopy (SEM) and color/gloss measurements. It has been observed that calcite addition affects the transparency, color and surface texture of the standard seal. It has been observed that as the amount of calcite increases in the glaze formulation, some new phases are formed. From the analysis of these newly formed peaks, it was found that the new phases are the Ca-silicate phase varieties and especially the wollastonite (CaSiO3). Addition of calcite in the ratio of 40 % increased the sintering temperature by 210 °C