Mineralogical Studies on Inorganic Pigment

Jung Hyun Yun

Department of Earth and Environmental Sicences
Graduate School, Andong National University
(Supervised by professor Jeong Jin Kim)

Abstract

Mineral colorants are made with minerals from nature and the most widely used colorants are Noerok in green and Seokganju in red.
The purpose of this study was to study the mineralogical characteristics of Seokganju and Noerok that are used for Dancheong and the Fe-oxide and Al-oxide synthesized in a lab, and to measure the change in chromaticity of colorants produced in various ways to suggest the optimum method of making mineral colorants. Seokganju, Noerok, Fe-oxide, and Al-oxide for the study were separated by particle size and the quantitative analysis of minerals was performed using X-ray diffraction analysis and SIROQUANT to identify the types of minerals in each sample and their ratios. Also, SEM and SEM-EDS analysis were performed to analyze the surface properties and composition of each sample. To observe the color change by temperature change, color difference analysis was performed using the L, a, and b values.
As a result of XRD analysis, the components of Seokganju were quartz, muscovite, and hematite. Hematite contents increased with larger particle size. The main components of Noerok were celadonite, muscovite, and quartz. With larger particle size, there tended to be less celadonite and greater quartz. Al-oxide is amorphous, but Fe-oxide is mostly composed of goethite and magnetite. With larger particle size, there tended to be less goethite and greater magnetite.
As a result of analyzing the color difference by temperature, Seokganju darkened slightly with less red as the temperature increased, while Noerok darkened slightly with darker red. Fe-oxide changed from red to red-brown and increased in brightness as the temperature increased, but Al-oxide dramatically lost its brightness and turned black at 300°C.
Since the old times, the Korean ancestors found colors in nature to make colorants in order to express beauty. As a result, we are able to appreciate countless artworks. Noerok and Seokganju, the mineral colorants used for this study, have been used since the old times and appear green and red, respectively, which are the major colors of nature. Also, acid mine drainage (AMD) is rich in dissolved metals. These dissolved metals form sediments in the form of hydroxide according to pH change.
The purpose of this study was to divide the components of mineral colorants and chemical colorants into micro particles for an analysis to clarify the mineralogical characteristics of each particle. For this purpose, Al sulfate and Fe sulfate for chemical colorants were dissolved in 0.1M HC l(pH 1) for 10,000 ppm and NaOH was added to make pH 6. The sediments containing Al Oxide and Fe Oxide were divided into 130 um and 260 um in micro units. Seokganju and Noerok for the colorants were pulverized to divide Noerok into 10, 15, 20, 40, 80 um and Seokganju into 100, 130, 260 um. XRD, SEM, and SEM-EDS were mineralogically analyzed by particle size. The samples that were divided by particle size for the chromaticity analysis by temperature were observed under different temperatures using an electric furnace.
As a result of analysis, 260 um Fe Oxide contained greater Geothite and less Magnetite compared to 130um Fe Oxide. In both SEM and EDS, Geothite content increased and Magnetite content decreased. Seokganju, as a result of XRD analysis, Quartz, Muscovite, and Hematite contents increased with higher micro units. However, Albite content decreased. As a result of SEM and EDS analysis, Quartz, Muscovite, and Hematite contents increased with higher micro units. Noerok, as a result of XRD analysis, lost Quartz content up to 10∼20 um particle size. Muscovite and Celadonite contents increased, but Quartz contents increased in 40-80 um while Celadonite contents decreased. Celadonite contents also decreased in SEM and EDS analysis. XRD analysis could not apply to Al Oxide as it is amorphous, but O contents changed as a result of SEM and EDS analysis.
As a result of color difference analysis by temperature and chromaticity analysis of Seokganju, there was no difference after mixing with the original sample using glue, but the concentration and brightness of red decreased closer to 100°C-300°C. The color appeared dark red at 300°C and increased in brightness after 300°C. Red and yellow concentration also decreased with less brightness at 900°C.
There was no difference after mixing with the original sample using hydraulic elutriation, but the concentration and brightness of red decreased closer to 100°C-300°C and increased again after 300°C. The concentration of yellow decreased up to 200°C and tended to rise again after 200°C. Both brightness and concentration decreased after 900°C.
As a result of chromaticity analysis of Noerok, the brightness tended to be darker and the concentration of red increased gradually after mixing with the original sample using glue. The concentration of yellow decreased down to 100°C-500°C and tended to darken the green color. It turned closer to brown after 500°.
The brightness increased after mixing with the original sample using hydraulic elutriation, but decreased after 100°C until it tended to rise again after 250°C. The concentration of red tended to decreased up to 200°C and rise again after 250°C. The concentration of yellow tended to decrease up to 100°C and increase after 250°C. It became close to brown after 500°C.
As a result of analyzing the chromaticity of Fe-Oxide, there was no difference after mixing with the original sample using glue, but the color tended to turn red-brown and the brightness tended to increase after 200°C. After mixing with the original sample using hydraulic elutriation, the color turned purple after 200°C.
As a result of chromaticity analysis of Al-Oxide, there was no difference after mixing with the original sample using glue, but the brightness burned as the temperature increased from 0°C to 500°C. The glue mixture promotes coagulation. When mixed with the original sample using hydraulic elutriation, no burning occurred as with the glue mixture. There was no prominent color change.