The mechanism of red color formation of red clay for Japanese rakuyaki

Red clay, the raw material for making rakuyaki, has long been produced in the vicinity of Kyoto, Japan. However, red clay deposits in this area are being exhausted due to the long time collection for the past 400 years as well as the housing land development. For this reason, many potters in Japan began in earnest to regain the genuine red color of raku by developing red clay containing iron from the regions other than Kyoto such as Shigaraki city (Shiga, Japan) (5)). In this study, we analyzed out the chemical and physical properties of red clay collected from Shigaraki and examined the mechanism by which red color is developed at the firing temperature of 900 degrees C. X-ray fluorescence analysis showed that Shigaraki red clay contains SiO2 (60.63%), Al2O3 (26.03%), and Fe2O3 (9.43%), suggesting that it contains higher iron content than red clay collected in Korea. Results from Raman spectroscopy indicated the mechanism of red color development in which chemical transformation of Goethite [FeO(OH)] of Shigaraki red clay into Hematite (Fe2O3), and the subsequent formation of solid solution with Alumina (Al2O3) and Silica (SiO2). In addition, in UVanalysis L*, a*, b* color space of Alumina and Silica was 46.44, 25.47, and 16.56, and 50.83, 28.12, and 20.44, respectively. (C) 2014 The Ceramic Society of Japan. All rights reserved.