THE COLOR CHANGES WITH THE FINNISH EARTHENWARE CLAY AND CALCIUM OXIDE IN STONEWARE GLAZES

The Finnish Earthenware clay is a low fired composition. It has high iron content and gives red coloring effect after firing. The Analyze of The Finnish Earthenware is very like the famous Albany Slip from Canada. As low fired clay it is useful for the ceramist artist as a plastic clay material, but it is also available to mix in powder form with the different raw materials and to fire as stoneware slip glaze. The Calcium oxide gives with iron oxide different red brown or yellow colors. For this case calcium raw materials, such as whiting, dolomite, and wollastonite have been chosen. The amount of the Earthenware is used between 50-90% of the glaze. For the testing and the comparing the glazes have fired in oxidation and reduction atmosphere. The iron oxide turns easily color from the yellow brown to green depending on the kiln atmosphere and the amount of the oxide. Calcium oxide helps the color changes to turn from yellow to green tones in stoneware temperature. The color tone changes also during the practically glazing method. The thickness of the glaze surface gives different color tone. Thin surface is darker and the thick is lighter. The changes in the glazes have been analyzed with comparing oxides in the different empiric formulas.