It is assumed that clay soil with high Fe contents as its main ingredient was used in the red pigment layers on the surfaces of the Neolithic Age Red Painted pottery and the Red Burnished pottery in the Bronze Age that were excavated from the southern areas of the Korean peninsula. A variety of phases of iron oxides that form pigment layers were identified through X-ray diffraction analysis, Raman spectroscopy and Mössbauer spectroscopy in this study. In particular, although previous studies focused only on hematite as a pigment mineral, the Mössbauer spectra of pigment layers in this study showed a higher spectrum area ratio of sextet by ferrihydrite than that by hematite, implying that ferrihydrite in reddish-brown might have played a significant role in developing its color. In addition, as it can be seen in each specimen showing a different area ratio by site in the Mössbauer spectrum, compositions of Fe-containing minerals were different. It is assumed to have been caused by different ionic forms of iron in the soil materials and unstable firing atmosphere during Pit firing.
The purpose of this study is to scientifically analyze physicochemical characteristics of the roof tiles used for palaces in the Joseon Dynasty which stored in Changdeokgung material storage and Seooreung Jaesil and the modern handmade ones which made by N company to understand the differences between their manufacturing techniques. Through chromaticity, cross-sectional observation, component analysis, and crystal structure analysis, it was possible to confirm the physicochemical properties and fired properties of the roof tile. Roof tiles from the Joseon Dynasty have a wider colorimetric range and higher apparent porosity and water absorption, on average, than the modern roof tiles. The cross section of the Joseon Dynasty roof tiles shows that most clay minerals have not been vitrified, remaining in the form of atypical particles, while the modern roof tiles have denser clay materials. X-ray diffraction analysis identified low-temperature minerals such as micas in Joseon roof tiles but no peak of these minerals was observed in the modern roof tiles, implying that the modern ones are fired at higher temperature than the Joseon ones. Therefore, the modern roof tiles are fired at higher temperature and have higher density than the Joseon ones due to the use of pugmills. The general content of main ingredients was similar between the two. Additionally, the principal component analysis of trace elements in the Joseon roof tiles showed that most samples were from similar areas. It seems that the Joseon roof tiles were manufactured using soils supplied from a specific region at the same timeframe and their consistency in the content of principal components implies that they also have similar mix proportions of clay.
Iron oxides are the essential coloring oxides in traditional ceramic glazes. However, when Fe is involved in the coloration in the form of ions or colloids in glazes with low Fe content, it is difficult to identify the iron oxide phases. Generally, in many these glazes, Ca-rich minerals are observed by X-ray diffraction (XRD) or microscopic images, owing to their devitrification by the high Ca content. This study attempts to elucidate the correlation between the crystalline structure and coloration in the glazes while mainly focusing on neoformed Ca-rich minerals and Fe content. An experimental firing was carried out to produce tree ash glazes, with pine tree ash and Buyeo feldspar. In the case of oxidation glazes, the scanning electron microscopy (SEM) images and XRD patterns did not exhibit any Ca-rich crystals, and all the visible light reflectance spectra lines exhibited a similar shape. In contrast, the reduction glazes divided into blue glazes and other colored glazes according to the shapes of their reflectance spectra. It was confirmed that the influence of Ca-rich minerals on the glaze color was more pronounced than the blue color of the reduction glazes when the Ca and feldspar contents were sufficiently high and low, respectively, to form wollastonite. As the Ca content increased and the elemental composition of the reduction glazes changed, the neoformation of the Ca-rich minerals, such as wollastonite, anorthite, diopside, and akermanite was sequentially observed.
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