It is thought that the precipitation of lead compounds from solid solution (Ca, Pb)CO 3 is due to a temperature decrease. Since the tumulus was constructed more than approximately 1300 years ago, the diffusion velocity is very low. The diffusion depth is only 7–8 μm, as shown in Fig. Generally, as the temperature of stucco in a stone chamber of the tumulus does not rise above atmospheric temperature, the species diffused at near room temperature.
In the first stage, Pb in PbCO 3 diffused into CaCO 3 as a solute atom, and then, a solid solution, (Ca, Pb)CO 3, was formed. It is thought that Pb species diffused into the CaCO 3 crystal from PbCO 3 coated on the stucco (CaCO 3). Transmission electron micrograph of Pb 2O 3 precipitates in CaCO 3 and the electron diffraction pattern from the position circled.
It is well known that cerussite in hot water changes to white lead, and the compound has been synthesized since olden times. The main pigments used in the mural -cinnabar (HgS) 2, 3), iron oxide (Fe 3O 4) 4), malachite, a similar white Pb compound, has been used for cosmetics. The clarification of the pigments and painting technique used on the mural is very important in identifying ancient techniques and also for conserving the precious cultural property. The Takamatsuzuka tumulus mural is the oldest genuine picture in Japan and was drawn at the terminal stage of the Kofun period 1). This Paper was Originally Published in Japanese in J. It is thought that the lead carbonate is coated on the stucco. These grains are formed by the reaction between the lead carbonate and the CaCO 3 matrix. The size of the lead oxide in CaCO 3 is 10–500 nm. On the layer under the surface layer, CaCO 3 grains containing lead oxide precipitates, that is, Pb 3O 4 and Pb 2O 3, and CaCO 3 grains containing Pb atoms are observed. The surface layer consists of fine lead carbonate grains with a size of 100–200 nm. The latter absorption edge is caused by Fe ion contained in the surface layer. Although the absorption edges of the white stucco CaCO 3 and ocher area on the surface are approximately 2.8 and 2.0 eV respectively, the dull ocher area does not show the absorption edge. The surface of the specimen consists of three colored areas white, dull-ocher, and ocher. A spectroreflectometer, a scanning electron microscope, and a transmission electron microscope are used to analyze the microstructure. The purpose of this research is to clarify the existing condition of Pb near the stucco surface. The microstructure of the stucco surface containing Pb of the Takamatsuzuka tumulus, constructed in the 7th–8th century, has been investigated.
0 kommentar(er)
