Reproduction of Japanese traditional pigment based on iron oxide powders with yellowish red color

Since the beginning of the 18th century A.D., an artificial iron oxide pigment (hematite, called "bengara" in Japanese) and having a beautiful yellowish red color, has been produced in Japan and applied to pottery, textiles and paintings. However, in 1965 the traditional "bengara" could not be produced anymore, mainly because of environmental pollution. The purpose of this study is to make clear the features of traditional "bengara" and to reproduce high quality "bengara" using modern high-purity reagents. Traditional "bengara" has been characterized as hematite containing a small amount of Al. The average size of the "bengara" particles is approximately 100 nm. The color becomes more yellowish-red with increasing Al content. A monophase of hematite prepared by heating a mixture FeSO₄-7H₂O and α-Al₂O₃ to about 680°C included a small amount of Al substituted in a solid solution. The particle size greatly decreased as the heat treatment temperature was decreased : 100 nm at 770°C but 50 nm at 650°C. The color of the particles becomes more vivid as the temperature is decreased, but within bounds this color is independent of the amount of Al in solid solution.