4:00 PM - 4:15 PM
[HTT21-03] Conservation restoration of the world heritage of Okinawa Prefecture, Sonohyan-utaki Ishimon - Situation after 30 years since filling with mortar and applying silicone resin.
Keywords:Stone cultural heritage, Restoration, Okinawa , Limestone, Colorimeter
Sonohyan-utaki Ishimon in the Shuri Castle Park has been registered as a World Heritage Site in 2000 as a place of "Gusuku and related heritage group of the Ryukyu Kingdom". The stone gate (Ishimon) and the forest behind it are called Sonohyan-utaki and used as a place of worship for praying for safety when the King of the Ryukyu Kingdom goes out. It was built with Ryukyu Limestone in 1519, was designated as the old national treasure in 1933 but was destroyed in the battle against Okinawa, was restored in 1957, and repaired in 1986. It became the national designated building in 1972. At the time of demolition repair, an old roof stone was used, but cleaning and water repellent silicone resin impregnation and surface filling were done at this time. Currently, as can be seen in Figure 1, the color of the entire stone gate becomes darker, the difference in color between the filling part of the roof and the original stone is becoming noticeable. The purpose of this study is to be used for the repair treatment in the future.
In order to understand the color of the surface of the repaired roof and the overall color of the stone gate, quantitative measurements were made using a spectroscopic colorimeter (Konica Minolta, CM-700d) at 51 locations on the surface of the stone gate. The proportion of blackened parts was determined from the front of the stone gate using Photoshop. To measure the surface temperature of the stone gate, we grasped the temperature distribution of the surface using the FLIR thermal camera.
We installed a button type temperature and humidity measuring instrument in the upper left side of the stone gate with the permission of Naha City to grasp the change of temperature and humidity in the year-round. As a result of the measurement by the spectrophotometer, the color of limestone was bright, and it was almost the same color as the repair material in the roof part. However, the discoloration rate and the situation were different after 30 years. The repair material was gray, and it was found that the original stone was darker. The average annual temperature observed under the roof of the stone gate was 24 °c, and the average humidity was 81.5%, and the characteristics of the hot and humid subtropical climate were observed. The average temperature in winter was 22.1 °c, and the humidity was 80% and the lowest temperature was 8.5 °c. Therefore, it seems that the growth of vegetation is very fast and it may affect the color of rock surface.
In order to understand the color of the surface of the repaired roof and the overall color of the stone gate, quantitative measurements were made using a spectroscopic colorimeter (Konica Minolta, CM-700d) at 51 locations on the surface of the stone gate. The proportion of blackened parts was determined from the front of the stone gate using Photoshop. To measure the surface temperature of the stone gate, we grasped the temperature distribution of the surface using the FLIR thermal camera.
We installed a button type temperature and humidity measuring instrument in the upper left side of the stone gate with the permission of Naha City to grasp the change of temperature and humidity in the year-round. As a result of the measurement by the spectrophotometer, the color of limestone was bright, and it was almost the same color as the repair material in the roof part. However, the discoloration rate and the situation were different after 30 years. The repair material was gray, and it was found that the original stone was darker. The average annual temperature observed under the roof of the stone gate was 24 °c, and the average humidity was 81.5%, and the characteristics of the hot and humid subtropical climate were observed. The average temperature in winter was 22.1 °c, and the humidity was 80% and the lowest temperature was 8.5 °c. Therefore, it seems that the growth of vegetation is very fast and it may affect the color of rock surface.