Microstructure and coloring mechanism of purplish red shiso on Bizen stoneware

抄録

Bizen stoneware is produced by firing shaped green clay in a firewood kiln at around 1200 °C. A purplish red color referred to as shiso happens to appear on the stoneware, but does not appear on the same stoneware heated in an electric furnace. Shiso was found to be caused by the formation of an approximately 0.5 µm thick hematite (α-Fe₂O₃) layer by reaction between the Bizen clay and K supplied from the firewood. Purplish red-colored samples similar to shiso Bizen were successfully prepared by annealing at 1100 °C for 2 h in air after heating the Bizen clay pellets with K₂CO₃ at 1230 °C in a gas mixture of 10 vol % CO and 90 vol % Ar.