Development of Black Pigment Using Seokganju of Mountain Gyeryong

Abstract

We collected Seokganju minerals (regions in Gyeryong Mountain, Sangsin-ri, Banpo-myeon, Gongju Chungcheongnam-province), which were used as natural color pigments for grayish-blue during the 15th~16th centuries of the Joseon era, and investigated their crystallographic features to develop a black pigment having a spinel structure. By a Raman analysis, the color of Seokganju under transparent glaze as a pigment for painting was black because hematite (<TEX>$Fe_2O_3$</TEX>) in Seokganju was converted to magnetite (<TEX>$Fe_3O_4$</TEX>) However, Seokganju into the transparent glaze as a pigment was brown because of hematite (<TEX>$Fe_2O_3$</TEX>) and small amounts of maghemite (<TEX>${\gamma}-Fe_2O_3$</TEX>) in Seokganju minerals. Only Seokganju mineral is used, it is not suitable for black pigment into the transparent glaze. This study tried to develop a spinel crystal black pigment stabilized by Seokganju with CoO, <TEX>$Cr_2O_3$</TEX>, NiO, and <TEX>$MnO_2$</TEX> at <TEX>$1280^{\circ}C$</TEX>. A Raman spectroscopy analysis was performed to verify the presence of Mn The results showed that it existed as spinel, and two crystal phases <TEX>$CoFe_2O_4$</TEX> and <TEX>$MnFe_2O_4$</TEX> were mixed. <TEX>$CoFe_2O_4$</TEX> spinel has a dark grayish black color and <TEX>$MnFe_2O_4$</TEX> spinel has a greenish black color, and these two appeared as black. The color of a specimen calcined by adding 6 wt% of pigment mixed with 5 wt% of <TEX>$MnO_2$</TEX> added to lime glaze was analyzed with a UV spectrophotometer. When applying the color pigment, it appeared black stabilized with <TEX>$L^*$</TEX>24.23, <TEX>$a^*$</TEX> 0.12, <TEX>$b^*$</TEX> -2.29 at <TEX>$1260^{\circ}C$</TEX> oxidative calcination, With <TEX>$1240^{\circ}C$</TEX> reduction firing, it is appeared black stabilized with low brightness of <TEX>$L^*$</TEX> 23.13, <TEX>$a^*$</TEX> -1.12, <TEX>$b^*$</TEX> 0.54.